Bibliothek

Notizen: Using the ‘permutation of indices’ method proposed by Kaplan and Fraenkel, we could formulate the density-matrix equations required to fit the temperature-dependent 13C-NMR spectra observed with the title compounds. For 6Li13CHBr2 (1) and 6Li13CH2SC6H5 (2) an exchange mechanism is proposed by which monomers interchange C- and Li-atoms via a non-observed dimeric intermediate; the activation parameters of these intermolecular dynamic processes have been found to be ΔH≠ = 10.2 kcal/mol, ΔS≠ = 13.7 cal/mol·K for 1 and ΔH≠ = 11.1 kcal/mol, ΔS≠ = 20.6 cal/mol·K for 2 ((D8)THF as solvent). In the case of (6Li)butyllithium (3), the observed low-temperature spectra indicate that dimeric (3b) and tetrameric (3a) species are in dynamic equilibrium interchanging the C3H713CH2 groups (and THF molecules) bonded to the 6Li-atoms. The relative concentrations of the dimer and of the tetramer have been determined by peak integration or by line-shape fitting; the ‘pseudo’- equilibrium constant, defined by K′eq = [3b]2/[3a], was found to be 2.6·10-2 mol/1 (at -88°) and corresponds to ΔGR (-88°) = 2 ΔG°f(3b) - ΔG°f(3a) = 1.34 kcal/mol. The activation parameters of the dynamic process responsible for the exchange were estimated as ΔH≠ = 3.78 kcal/mol and ΔS≠ = -31.3 cal/mol·K. Tentative interpretation of the thermodynamic and kinetic parameters is given.

Notizen: On singlet excitation (λ = 254 nm, THF, pentane or hexane), the diastereoisomeric methano-epoxydienes (E)-6 and (E)-7 undergo interconversion and yield the products 8-11. The main process is the cleavage of the oxirane ring to the vinyl carbene intermediate e which undergoes addition to the adjacent double bond furnishing the cyclopropene 8. The alternative carbene intermediate f is evidenced by the formation of the cyclobutene 10. For the fragmentation leading to 11, the carbene f as well as the dipolar species h are considered as possible intermediates. On triplet sensitization (acetone, λ 〉 280 nm), (E)-7 shows behavior typical of epoxydienes, undergoing fission of the C—O bond of the oxirane ring and isomerization to the compounds 13, 14 and (E/Z)-15.

Notizen: The kinetics of the reaction (1) between 1,4,8,11-tetraazacyclotetradecane (Cy) and a series of Cu(II) complexes CuL (L) = glycolate, malonate, succinate, picolinate, glycinate, iminodiacetate, nitrilotriacetate, N-(2-hydroxyethyl)ethylenediaminetriacetate, ethyienediamine, 1,3-diaminopropane, diethylenetriamine and N,N-bis(3-aminopropylamine) were studied spectrophotometrically at 25° and I = 0.5 (KNO3). From the analysis of the log kobs/log [L] profiles obtained at different pH values the resolved bimolecular rate constants kCyHnCuLm (Table 3) were obtained by a nonlinear curve-fitting procedure. For nearly all systems studied, the rate constant kCyHCuL, describing the reaction between the 1:1 complex CuL and the monoprotonated form of the macrocycle CyH, was obtained. The nonlinear relationship between log kCyHCuL and log KCuL and its nature is discussed. It is shown that the inverse relationship between reactivity and stability described by others is only a special case of the more general Eqn. 3 described here.

Notizen: Kinetics of Monomolecular Surface Modification of 4-(Trichlorosilylmethyl)benzonitrile on Germanium by Means of FTIR ExperimentsA Fourier transform-attenuated total internal reflection-infrared spectroscopy (FT-ATR-IR) technique is described, which allows to observe the kinetics of monomolecular surface modification on materials which are feasible to total internal reflection experiments in an appropriate wavelength region. First results are reported for the reaction of 4-(trichlorosilymethyl)benzonitrile on germanium. The reaction is slower than expected and is only completed after approximately 4 h.

Notizen: Structure Elucidation of (Hydroxy-oxo-cyclopentenyl)alkanoic Acids, the Aldol-Condensation Products of Dioxoene Acids from Cattle LiverDuring homogenization of cattle liver the highly instable dioxoene acids 13a, 13b, and 13c are formed. These acids cyclize in alkaline solution to yield pairs of stable (hydroxy-oxo-cyclopentenyl)alkanoic acids, which were isolated as methyl esters 4a/5a, 4b/5b, and 4c/5c. The structures of these compounds were deduced from an enriched 3-mg mixture sample by microchemical reactions combined with a GC/MS analysis of the reaction products. Compound 13a was obtained as methyl ester by oxidation of the methyl ester of the corresponding F-acid with NaOCl. It was not possible to isolate 13a in pure form due to its high sensitivity. Instead of the methyl ester of 13a, 4a and 5a were isolated, of which the structures were established.

Notizen: Lithium alcoholates prepared in situ react spontaneously with imidazolides derived from substituted aromatic carboxylic acids to provide the amino-esters 4 in excellent yield.

Notizen: The synthesis and characterization of the novel 4,7-bis(dialkylamino)tricyclo[5.2.1.04,10]deca-1(10), 2,5,8-tetraenes 12 from 1,4,7-trihalotriquinacenes 8 and secondary amines is reported. The structural and electronic characteristics of these as well as the acepentalene dianion (32-) and some related systems as determined by semiempirical (MNDO) calculations are discussed. Thereby, 32- should be a triply etheno-bridged trimethylenemethane dianion exhibiting Y-delocalization favored over the formation of a peripheral 10π-electronic system. Attempts directed towards the generation of 32- by reacting tetraenes 12 with Na led to the formation of tris(dialkylamino)triquinacenes 9, presumably by a kind of reduction/disproportionation mechanism.

Notizen: Total Synthesis of Decarboxybetalaines by Photochemical Ring Opening of 3-(4-Pyridyl)alanineA photochemical approach is presented for the total synthesis of the decarboxybetalaines, which were previously known from the mild decarboxylation of the natural plant colorants, the betalaines: Irradiation of rac-3-(4-pyridyl)alanine (1) yielded the rac-2-decarboxybetalamic-acid-imine (4, 86%), presumably via a Dewar pyridine 2, a cyclic aminal 3 and an electrocyclic ring opening. The imine-zwitterion 4 was treated with three amines, namely (S)-cyclodopa (6), (S)-proline (7), and indoline (8), to afford three decarboxybetalaines, namely (2S)-17-decarboxybetanidine (9, red, 34%), (2S)-13-decarboxyindicaxanthine (10, yellow, 56%), and rac-16-decarboxyindobetalaine (11, orange, 78%), respectively. The structures of these coloring matters were confirmed by their electrophoretic behavior and their spectroscopic properties. 17-Decarboxybetanidine 9 was shown to be a ca. 1:1 mixture of two C(15)-epimers 9a and 9b, separable by chromatography. The configuration of 9a was determined as (2S, 15S) and that of 9b as (2S, 15R), by correlating their optical rotations with those of betanidine (12a) and isobetanidine (12b), respectively. The decarboxybetalaines 9, 10, and 11 did not show the double-bond isomerism at C(β), (Cγ) of the chromophore which had been found characteristic for the corresponding betalaines 12, 13, and 14.

Notizen: Monoterpene Alkaloids of Scaevola racemigera DÄNIKERNine alkaloids have been isolated from the aerial parts of Scaevola racemigera. Two of them are the known compounds cantleyine (1) and tetrahydrocantleyine (2). The seven others are novel alkaloids, strychnovoline (3), 6-O-nicotinoylstrychnovoline (4), 6-O-nicotinoyltetrahydrocantleyine (5), 6-O-(5-vinylnicotinoyl)tetrahydrocantleyine (6), racemigerine (7), 6,7-epoxyracemigerine (8), and scaevoline (9). The structures of the new compounds have been elucidated by their spectral data and confirmed by chemical correlations. Moreover, the absolute configuration of 2, which had not been previously determined, has been elucidated.

Notizen: The stereoselectivity of the cycloadditions of 2-(D)methylidene-3-methylidenebicyclo[2.2.1]heptane (4) to various dienophiles has been determined. The exo- vs. endo-face selectivity depends on the type of dienophiles, and for olefinic ones, on the mode of attack (Alder- vs. anti-Alder endo rule). It is 〉 9:1 with N-phenyltriazolinedione (NPTAD) and ethylenetetracarbonitrile (TCNE), 〈 1:9 with dimethyl acetylenedicarboxylate (DMAD), 30 ± 5:70 ± 5 with DMAD in the presence of AlCl3, 15 ± 5:85 ± 5 with dehydrobenzene and 40 ± 5:60 ± 5 with 1O2 generated photochemically (Table 1). With para-benzoquinone and maleic anhydride, the exo- vs. endo- face selectivity is 〈 1:9 and 20 ± 5:80 ± 5, respectively, for their anti-Alder mode of attack; it is 50 ± 5:50 ± 5 and 55 ± 5:45 ± 5, respectively, for their Alder mode of reaction. Under conditions of kinetic control, the chelotropic addition of SO2 to 4 is endo-face selective.

Notizen: The hypothesis which explains the diastereoselectivity of the 1,3-dipolar cycloaddition of the N-glycosylnitrones 1-3 leading to the 5,5-disubstituted isoxazolidines 4-6 on the basis of a kinetic anomeric effect predicts that nucleophiles should add to N-glycosylnitrones with a high degree of diastereoselectivity. To test this prediction, the nucleophilic addition of lithium and potassium dialkylphosphites to the crystalline (Z)-nitrone 11, prepared from oxime 9 and (benzyloxy)acetaldehyde has been examined. The addition of lithium phosphites gave the N-glycosyl-N-hydroxyaminophosphonates 12-16 (d. e. 78-92%) in high yields (Scheme 4). The addition of potassium phosphites showed a much lower diastereoselectivity. Glycoside cleavage, hydrogenolysis, and dealkylation of 12-16 gave (+)-(S)-phosphoserine (+)-19 (34-45% from 9). Its absolute configuration was confirmed by an X-ray analysis of the N-(3,3,3-trifluoro-2-methoxy-2-phenylpropionyl) derivative 24. Similarly, the crystalline nitrone 25 gave the N-glycosyl-N-hydroxyaminophosphonate 26, which was transformed into (+)-(S)-phosphovaline (+)-31 (42% from 9). The diastereoselectivity of the nucleophilic addition and the enantiomeric purity of (+)-31 were determined by the analysis of the derivative 30 (d.e. 92%) and 32 (d.e. 93%), respectively. The addition of lithium diethyl phosphite to the nitrone 33, prepared in situ, gave the N-glycosyl-N-hydroxyaminophosphonate 34, (41%; d.e. 91%), which was transformed in (+)-(S)-phosphoalanine (+)-37 (21% from 9).

Notizen: The yield of the main product from the reaction of heptamethyl dicyanocobyrinate with O2 in the presence of ascorbic acid has been optimised by systematic variation of the reaction conditions, and the structure of the obtained ‘stable yellow corrinoid’ has been established by X-ray analysis. From the relationship between the structures of analogous xanthocorrinoids obtained likewise from a series of dicyanocobyrinic-acid derivatives, which has been prepared by systematic modifications of the c-acetic-acid chain, and the functionality of the substituent at C(7), a reaction mechanism is suggested.

Notizen: Ring Expansion during the Reaction of a 1,3-Cyclohexanedione with DiphenylcyclopropenoneThe reaction of 5,5-dimethyl-1,3-cyclohexanedione (1) in form of its Na-salt with diphenylcyclopropenone (2) in DMF yielded the bicyclic triketone 3 (58 %), the structure of which was deduced as an enolizeable bicyclo[5.2.0]nonane-β-diketone from spectral data and from the following reactions: hydrolysis or methanolysis of 3 cleaved the β-dicarbonyl moiety, thereby opening the 4-membered ring to yield the keto acid 9 or its methyl ester 10. Methylation of 3 afforded the two enol ethers 4 and 5. The ether 5 readily underwent a thermal electrocyclic ring opening to the monocyclic enol ether 8, whereas the ether 4 was thermally stable. The same electrocylic ring opening (in boiling benzene) converted 3 (probably via 3b) to the monocyclic triketone 7, which was also the hydrolysis product of the ring-opened enol ether 8. By heating 3 in DMF/H2O, a partial (56 %) conversion to the lactone 6 took place. The tricyclic intermediate 11 was found useful to rationalize the ring expansion during the formation of 3 from 1 and 2 as well as the corresponding ring contraction during the conversion of 3 into 6.

Notizen: Determination of the Chirality Sense of the Enantiomeric 2,6-AdamantanediolsThe enantiomers of 2,6-adamantanediol (1) are resolved via the diastereoisomeric camphanoates. The (2R,6R)-chirality sense for (-)-1 and (2S,6S) for (+)-1 was determined by chemical correlation with (-)-(1R,5R)-bicyclo[3.3.1]nonan-2,6-dion ((1R,5R)-3) of known absolute configuration in the following way: alkylation of the bis(pyrrolidine enamine) of (-)-(1R,5R)-3 with CD2I2 and hydrolysis of the product gives the enantiomer 4 of (4,4-D2)-2,6-adamantanedione. Reduction of 4 with LiAlH4 leads to one enantiomer (Scheme 2) of each of the three diols 5-7 of known absolute configuration. The three diols are themselves configurational isomers due to the presence of the CD2 group, but correspond otherwise entirely to the enantiomeric diols 1. Accordingly, they can also be separated by means of their diastereoisomeric camphanoates to give the diols 5/6 and 7. These samples are easily distinguished and identified by their characteristic 1H-NMR spectra (cf. Fig. 2). This allows to identify the (2R,6R)- and (2S,6S)-enantiomer of 1 on the basis of their behavior in the resolution experiment analogous to that of the diols 5/6 and 7, respectively. The diol (-)-1 must have the (2R,6R)-configuration because it forms, like the diols 5/6, with (-)-camphanic acid the diastereoisomeric ester less soluble in benzene. The diol (+)-1 has (2S,6S)-configuration, because it forms, like 7, with (+)-camphanic acid the diastereoisomeric ester less soluble in benzene. The bis(4-methoxybenzoate) of (-)-(2R,6R)-1 shows chiroptical properties which are in accordance with Nakanishi's rule for two chromophores having coupled electric dipol transition moments arranged with a left-handed torsion angle.

Notizen: Asymmetric disulfide conjugates of mercaptosuccinyl tobacco mosaic virus (TMV ∼ SH) with Nα-desacetyl-Nα-5-(mercaptovaleryl)-α-melanotropin were prepared via the S-sulfoderivative of the peptide. The conjugates, TMV ∼ S—S ∼ α-MSH(n), contained up to n = 330 disulfide-linked peptide molecules/virion. Similarly, fluorescent conjugates, Rh(m) ∼ TMV ∼ S—S ∼ α-MSH(n) were prepared, containing m ≍ 200 rhodamine molecules linked to the virions by thiourea bridges. Such conjugates were designed to study α-MSH receptor localization and dynamics (mainly internalization), because the carrier virions which served to enhance specific receptor binding and as fluorescent or radioactive markers may be detached from the neuropeptides at will by reduction. Reduction occurred in solution and on the cell surface, but not in the cytoplasm, thus allowing detection of internalized agonist-receptor complexes. The conjugates were superpotent agonists for tyrosinase stimulation in Cloudman S-91 melanoma cell cultures, but were inactive for cyclic AMP accumulation. Their rather rapid internalization and the influence of reducing agents and other agonists on their biologic activity suggest a close connection between receptor location and biologic response as well as the presence of essential receptor HS-groups.

Notizen: Halochromic Molecules. Synthesis of Substituted 6H-Chromeno[4,3-b]indolizines and their Aza-analoguesWe have synthesized a series of substituted chromeno[4,3-b]indolizines and their respective aza-analogues. Dyes generated from them contain the electrondonating 2-(2-hydroxy-5-methylphenyl)indolizin-3-yl moiety. The 90 MHz FT 1H-NMR spectra of starting and final products supported the postulated structures. Fragmentations in the mass spectra also were consistent with the assumed structures.

Notizen: Reaction of glutarimide with pent-4-enylmagnesium bromide, followed by cyclization of intermediate ketoamide, and hydrolysis of the formates 10 and 13 led to the mixture of the hydroxylactams 11 (cis) and 14 (trans) which could be separated via their benzenecarbamates. Reduction of cis-hydroxylactam 11 with LiAlH4 yielded 2-depentyl-7-debutylperhydrohistrionicotoxin (6), whereas reduction of trans-isomer 14 gave the epimeric alcohol 9. cis-Hydroxylactam 11 was converted via thiolactam 17 and the methylthio derivative 18 to ketimine 19 which was reduced with NaBH4 yielding a mixture of natural 4 and unnatural 7, analogues of perhydrohistrionicotoxin (2). Reduction of 4 with H2 in the presence of Pd/C yielded (±)-7-debutylperhydrohistrionicotoxin (5).

Notizen: β-Functionalized Hydrazines from N-Phthalimidoaziridines and their Hydrogenolytic N,N-Cleavage to AminesThe three N-phthalimido-aziridines 1-3 were reacted with phenol, thiophenol, aniline, p-toluenesulfonic acid, and H2O in selected combinations. These nucleophiles opened the 3-membered ring to yield the N-phthalimidoamines 4a-d, 5a-d, 6a-c, and 6e; all these products (except the carbinol 6e) carry an aryl-substituted functional group on the C-atom vicinal to the N-substituent. Hydrazinolysis of 4, 5, 6a-c, and 6e afforded the β-functionalized hydrazines 7, 8, 9a-c, and 9e. The reducing medium Raney-Ni/N2H4 transformed 4, 5, 6a-c, and 6e to the β-functionalized amines 10, 11, 12a-c, and 12e. By a study with the hydrazide 6a and the hydrazine 9a, it was shown that the N,N-cleavage is a catalytic hydrogenolysis by H2 generated from N2H4 with Raney-Ni and that it does not take place on the hydrazide 6, but rather on the hydrazine 9, generated as intermediate from 6 with N2H4. Spectroscopic data confirmed that the conversions of 1-3 to 4-6 occurred exclusively with inversion and that the resulting configurations remained fully intact during the transformations of 4, 5, and 6 (via 7, 8, and 9) to 10, 11, and 12, respectively.

Notizen: Electrochemical Synthesis of the Ni(O)-Diazabutadiene ComplexesThe electrochemical reduction of Ni salts in the presence of diazabutadiene ligands (DAB = R—N=CH—CH=N—R, R = t-Bu, o-xylyl, p-anisoyl, p-tolyl) has been studied in DMF by cyclic voltammetry and rotating disc polarography. In solutions containing DAB and halide X-, Ni(II) can be reduced to Ni(DAB)2, and the features of this reduction agree with a mechanism where the second DAB replaces X- in the coordination sphere of Ni only after its reduction to Ni(O). Rather concentrated (≃ 0.1M) solutions of NiBr2 · DME and DAB in DMF have been electrolyzed without a supporting electrolyte, making the isolation of the product Ni(DAB)2 particularly easy. Thus, gram quantities of Ni(DAB)2 can be conveniently prepared within a few hours.

Notizen: The synthesis of five macrobicyclic polyamines 1-5 is described following a route in which the macrobicycle is formed by the coupling of two tripodal subunits. Such a sequence is appreciably shorter than the stepwise construction via a macrocycle, and may give higher yields, as illustrated by the case of bis-tren 3, which has been synthesized following both routes.

Notizen: Tritylketones and Tritylenones. Contributions to the Sterically Enforced Michael Addition and to the Diastereoselective Aldol AdditionTritylketones are prepared from trityllithium and aldehydes, with subsequent CrO3 oxidation (Scheme 1, 2a-f). Tritylenones are obtained from the saturated ketones and aldehydes or ketones, preferably by (CH3)3Al-mediated aldol addition with subsequent dehydration (Scheme 2, products 2e, 4b-e). The carbonyl of the tritylketone group is sterically protected, but electronically effective (see A-C); thus, amine-free enolate solutions can be obtained directly with BuLi; also, exclusive conjugate addition of organolithium derivatives occurs with tritylenones (Schemes 3-5, products 2d, 5-7, 15 examples). The lithiumenolates of tritylketones add to aldehydes with practically complete stereoselectivity (Scheme 6, products 10, 9 examples): due to the bulkiness of the trityl group, only the (Z)-enolates 8 are formed, and the approach of the two trigonal centers in the aldol-addition step is enforced to occur with relative topicity ul. As a first example of an X-ray structure determination of a silyl enol ether, the crystal structure of (Z)-2-(trimethylsilyloxy)-1, 1, 1-triphenyl-2-butene (9) is reported. Fortunately, the blocking of the carbonyl group in trityl ketones can be run very specifically (without epimerization at the α-carbonyl center) by lithium triethylborohydride to furnish, after aqueous workup, primary alcohols and Ph3CH (Eqn. 4, products 13-20, 10 examples); the OH-group of the aldols 10 must be EE-, MOM- or MEM-protected (Scheme 8) before this C,C-bond cleavage can be conveyed. Some of the cleavage products are used for the chemical correlation of the aldol configuration and for the demonstration of the synthetic value of the presented method (see 21-29).

Notizen: A cell-free extract, which was isolated from the leaves of mature Catharanthus roseus plants by a previously published procedure, does not convert a mixture of secologanin and radiolabelled tryptamine to vindoline, as was recently claimed. The radioactivity in the purified alkaloid extract determined by earlier workers is certainly due to ‘impurities’ in the presumed ‘vindoline’. This was shown by extensive purification of the alkaloid extract (which contained added unlabelled vindoline as a carrier) followed by chemical conversion of vindoline to two derivatives and subsequent purification, ultimately giving unlabelled deacetylvindoline.

Notizen: Reduction of 1,2-Bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzene1: Synthesis of Cyclotrisazobenzene ( = (5E,6aZ,11E,12aZ,17E,18aZ)-5,6,11,12,17,18-Hexaazatribenzo[aei][1,3,5,7,9,11]cyclododeca-hexaene)Na2S reduction of 1,2-bis[(Z)-(2-nitrophenyl)-NNO-azoxy]benzene (2) yielded 3 deoxygenated products: the (known) red 2,2′-((E,E)-1,2-phenylenbisazo)dianiline (3, 23%), the orange 2-[2-((E)-2-aminophenylazo)phenyl]-2H-benzotriazol (4, 55%) and the colorless 2,2′-(1,2-phenylene)di-2H-benzotriazol (5, 13%). The constitutions of 3-5 and of 6, the N-acetyl derivative of 4, were deduced from their 1H-NMR spectra (chemical shifts, couplings, and symmetry properties), and the configurations of 3, 4, and 6 at their N,N-double bonds are assumed to be the same as in 2. Oxidation of 3 with 2 mol-equiv. of Pb(OAc)4 afforded 5 (47%) and a novel, highly symmetrical macrocycle, called cyclotrisazobenzene (7, 24%). The constitution of 7 as a tribenzo-hexaaza[12]annulene and its (E)-configuration at the N,N-bonds was confirmed by X-ray analysis. The molecular symmetry expressed by the 1H-, 13C- and 15N-NMR spectra of 7 reveals a rapid torsional motion around the six N,C bonds. This implies that the N,N-double bonds in the cyclic 12π-electron system (or 24π-electron system if the benzene rings are included) of 7 are highly localized.

Notizen: Hyperfine coupling constants and g-factors determined by ESR and ENDOR spectroscopy are given for the radical anions of 21 syn-1,6:8,13-bridged [14]annulenes. The great majority of these values is reported for the first time. The hyperfine data are consistent with the single occupancy of an orbital which resembles a π-perimeter-LUMO of the same nodal properties. The sum of the coupling constants of the protons attached to the π-perimeter can be used as a planarity criterion for this perimeter.

Notizen: Rearrangements of (2′-Propinyl)cyclohexadienols and -semibenzenesThe acid-catalyzed dienol-benzene rearrangement of 3- and 5-methyl-substituted (2′-propinyl)cyclohexadienols has been investigated. Treatment of the dienols with CF3COOH in CCl4 yields allenyl- and (2′-propinyl)benzenes via [3,4]- and [1,2]-sigmatropic rearrangements, respectively. The reaction with H2SO4 in Et2O leeds to a mixture of allenyl-, 2′-propinyl-, 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 3). The latter are products of a thermal semibenzene-benzene rearrangement (cf. Scheme 9). The corresponding semibenzenes have been prepared by dehydration of the cyclohexadienols with H2SO4 or POCl3 (Schemes 6 and 7). Under acidic conditions, the p-(2′-propinyl)semibenzenes 33-35 (Scheme 8) undergo [3,4]- and [1,2]-sigmatropic rearrangements to give again allenyl- and (2′-propinyl)benzenes, whereas the thermal rearrangements to the 3′-butinyl- and (2′,3′-butadienyl)benzenes (Scheme 9) involves a radical mechanism. In contrast, the o-(2′-propinyl)semibenzene b (Scheme 7) leads to (2′,3′-butadienyl)benzene 32 via a thermal [3,3]-sigmatropic rearrangement.

Notizen: During the cob(I)alamin(1(I))-catalyzed reduction of 3, intermediate formation of 2 and final generation of 4-10 was observed (see Scheme 1, cf. Tables 1 and 2). Identical products in similar ratios were generated starting from either 2 or 3. Accepting the intermediate formation of six interconnected cobalt complexes, i.e. A-F (cf. Scheme 2), the generation of all the products observed can be explained.

Notizen: Using the readily accessible chiral auxiliaries 1-3 the sulfonamide-shielded O-silylated esters 5 underwent π-face-selective α-acetoxylation on successive treatment with Pb(OAc)4 and NEt3 HF to give after recrystallization α-acetoxy ester 6 in 55-67% yields and in 95-100% d.e. Starting from conjugated enoates addition of RCu and subsequent acetoxylation 10→11→12 yielded α,β-bifunctionalized esters 12 with 〉95% configurational control at both Cα and Cβ. Nondestructive removal of the auxiliary (6→7, 6→8 and 12→13) gave either α-hydroxycarboxylic acids or terminal α-glycols in high enantiomeric purity. The prepared glycols 8c and 13a are key intermediates for previously reported syntheses of the natural products 16 and 17, respectively.

Notizen: Synthesis and Reactions of the Bicyclo[6.4.0]dodecane-3-carboxylic Acid DerivativesThe synthesis and some consecutive reactions of the compounds 5-8, derivatives of bicyclo[6.4.0]dodecane-3-carboxylic acid (1), are described. The esters 7 and 8 can be obtained by Baeyer-Villiger oxidation of 2-hydroxy-8-methyltricyclo[7.3.1.02,7]tridecan-13-one (4) and subsequent hydrolysis of the lactone 5. The structure and configuration of these compounds has been evaluated by spectroscopic techniques (mainly 2D-NMR methods). The formation of 7 via 1,2-H shift and subsequent isomerization to 8 has been studied. The esters 11 and 13 are formed stereospecifically from 7 and 8.

Notizen: Reaction of 7,7-dimethoxy-5,6-dimethylidenebicyclo[2.2.1]hept-2-ene (2) with various metal carbonyls and their derivatives gave the η2-M(CO)4 (M = Fe (17), Ru (18)), η4-M(CO)3 (M = Fe (19x, 19n), Ru (20n)), and η2-M(CO)5 and η6-M(CO)3 (M = Cr, Mo, W) complexes. The trigonal bipyramidal η2-M(CO)4 complexes present an exceptional C3v symmetry at the metal with the C,C-double bond in an axial position. In all the η2-complexes, this double bond is stereospecifically coordinated by its exo-vs. endo-η4-Fe(CO)3 configuration was established by chemical correlation (hydrolysis, hydrogenation) with the corresponding complexes (24x, 24n) of 7,7-dimethoxy-2,3-dimethylidenebicyclo[2.2.1]heptane (5). The relative rates of hydrolysis (AcOH/H2O 2:1, 50°C) of ligands 2 and 5 and of complexes 19x, 19n, 24x, and 24n to the corresponding ketones showed an acceleration effect only when the metal is coordinated to the exo-face. This was attributed to an F-strain effect on the leaving group of the substrate. Compound 17 was further metallated by [Fe2(CO)9] giving the bimetallic isomers 21xn and 21xx. The endocyclic C,C-double bond of the latter can be stereospecifically hydroformylated (1 atm CO, AcOH/H2O, 25°C) giving 29x (49%). Hydroformylation of 17 gave the corresponding uncoordinated aldehydes 30x/30n in better yields (76%) but with lower selectivity (3:1). These are the first examples of hydroformylation of an isolated [Fe(CO)4(olefin)] complex.

Notizen: Syntheses of Positionisomeric Alkoxyformylderivatives of 1,6-Methano[10]annulenesDifferent aldehydes of 1,6-methano[10]annulene - namely 3-6, 11, 12, 15, and 19 - were synthesized. They can be used as starting materials for synthetic reactions of other new bridged systems; the results of 1H-NMR- and 13C-NMR measurements are included.

Notizen: The stereoselective glycosylation of alcohols and their silyl ethers has been achieved using O-alkyl-, O-acyl-, and acetal-protected glycosyl fluorides of the pyranose and furanose series and boron trifluoride etherate in CH2Cl2.

Notizen: Two methods for stereoselective β-glycosylation of digitoxose were developed. The first achieved stereocontrol by a 1,3-participation of a N-methylurethane group under acid catalysis. The second utilized mercuric-ion catalyzed cleavage of thioglycosides and a 1,3-participation of a p-methoxybenzoyl group in a neutral medium. The first highly stereoselective and quite efficient synthesis of digitoxin (C7) was achieved by a combination of these methods. The furyl-substituted precursor IV of digitoxigenin (Scheme 1) was used as aglycone, and the furan group was converted to the unsaturated lactone of digitoxin by our known oxidation procedure (m-chloroperbenzoic acid/NaBH4) after the assembly of the carbohydrate portion of the molecule and its deblocking was completed.

Notizen: Induced by a stoichiometric excess of dichloro(diisopropoxy)titanium, 1-(trimethylsiloxy)cyclohexene and p-substituted β-nitrostyrenes (Y = H,CH3,CH3O,CN) combine in CH2Cl2 solution at -90° preferentially with relative topicity ul - opposite to the corresponding reaction of enolates or enamines. The primary products are the bicyclic nitronates 3-5 which can be separated, and which are cleaved by KF in MeOH to give the aryl(nitroethyl)-substituted cyclohexanones 1 and 2 (Tables 1 and 2, two typical procedures are given). The major products (2:1 to 4:1) are the hitherto not readily available diastereoisomers 2 of l-configuration. Instead of being solvolyzed, the bicyclic nitronate 5 can be used for nitroaldol additions (→6) and for [3 + 2]-dipolar cycloadditions (→7), diastereoselectively furnishing products with 4 asymmetric C-atoms (not counting acetal centers). The Michael addition described here is yet another example of an ul-combination of trigonal centers induced by Lewis acids, overriding the influence of the configuration of the donor component.

Notizen: A short synthesis of the title compound 13 is reported. The acetal group in 13 enables one to control the regio- and stereoselectivity of the two successive Diels-Alder additions of the tetraene. The first addition is significantly faster than the second one, thus making 13 a versatile reagent for regio- and stereoselective ‘tandem’ cycloadditions.

Notizen: As a further application of the cyclopentenone formation A→C via the thermal α-alkynone cyclisation B→C and in order to test the fate of an isolated C,C-double bond within a molecule under these conditions, we investigated the synthesis of the acorone intermediate 3starting from the known carboxylic acid 1. The α-alkynone 2 was obtained from 1 via the acyl chloride 6 and a Pd(II)-catalysed route (22%). The thermolysis of 2 at 550° provided the target molecule 3 (48%) together with the product 9 (20%) of a competing intramolecular ene reaction and its dimer 10 (4%). At a higher thermolysis temperature (650°), the spiro ketone 3 was found to be unstable, affording the retro-Diels-Alder fragments 4-methylidene-2-cyclopentenone (12) (33%) and isoprene (32%). A further example of the influence of an isolated double bond on the yield of the cyclopentenone-formation sequence A→C was provided by the comparison of the annelation 14→20 (5% overall with Pd(II)-catalysed acylation) with that of its non-olefinic analogue 17→21 (53% overall with Friedel-Crafts acylation).

Notizen: The title compound (1) is prepared in situ from 5-methylenebicyclo[2.2.0]hex-2-ene by pyrolysis and subsequent photoionization in a photoelectron spectrometer or by X-ray irradiation in an Ar matrix where its electronic absorption spectrum is obtained. The results confirm earlier conjectures that the title cation exists as a distinct entity on the C7H8+ hypersurface and can be obtained photochemically from other isomeric ions or by a McLafferty rearrangement. The enthalpies of formation of 1, its precursor and the corresponding radical ions are compared to the most recent data available for other C7H8 isomers and their ions. It is shown that the thermodynamic stability of 1+ is closer to that of toluene cation than concluded on the basis of earlier results.

Notizen: The radical anions of [2.2]paracyclophane-1,9-diene (2) and its 1,10,12,13,15,16-hexadeuterio derivative 2-D6, as well as those of 4,5,7,8-tetramethyl[2.2]paracyclophane-1,9-diene (3) and its 12,13,15,16-tetradeuterio derivative 3-D4, have been studied by ESR spectroscopy. The coupling constants for 2-· at 178 K are 0.422 mT for four equivalent olefinic protons and 0.046 and 0.020 mT, each for a set of four equivalent aromatic protons. This hyperfine pattern is consistent with either benzene ring bearing two pairs of equivalent protons and it points to a lowering of the anticipated D2h symmetry. The ESR spectra of 2-· are strongly temperature dependent, due to modulation of the two coupling constants of 0.046 and 0.020 mT; these have opposite signs and average to 0.013 mT at 273 K. The experimental findings are interpreted in terms of a transition state of D2h symmetry, 33 kJ/mol above two interconverting equivalent conformations of lower symmetry. Several pieces of evidence suggest that this symmetry is D2, i.e., the benzene rings in 2-· are twisted in opposite directions about the vertical axis. Temperature dependence of the ESR spectra, resulting from modulation of the hyperfine interactions with the aromatic protons, is also observed for 2-D6-· and 3-·. In the case of 3-·, the olefinic protons are, as expected, only equivalent in pairs, the pertinent coupling constants being 0.560 and 0.325 mT. Upon standing at low temperatures, 2-· and 3-· gradually convert into the radical anions of [2.2]paracyclophane (1) and its 4,5,7,8-tetramethyl derivative, respectively. At higher temperatures, cleavage of one bridging chain in 2-· also occurs, with the formation of the radical anion of (E)-4,4′-dimethylstilbene (7). Both reactions of 2-· must involve the transient radical anion of [2.2]paracyclophane-1-ene (4) as proved by the observation of the spectra of 1-· and 7-· with 4 as the starting material.

Notizen: It is shown that dimethyl 5, 6, 8, 10-tetramethyl- (3) and 8- (tert-butyl)-5,6,10-trimethylheptalene-1, 2-dicarboxylate (5), and their derivatives rearrange reversibly on irradiation or on heating to yield the corresponding 1,6,8,10-tetramethyl- (4) and 8-(tert-butyl)-1,6,10-trimethylheptalene-1,2-dicarboxylate (6), and their derivatives by double-bond shift (π-skeletal rearrangement) via a transition state with D2 symmetry as the highest possible one. This follows from the fact that (-)-(P)-3 is photochemically as well as thermally rearranged to give (-)-(P)-4 i.e. the π-skeletal rearrangement occurs with retention of configuration of the heptalene skeleton and without loss of optical purity.

Notizen: The BF3 · Et2O- and the CH3SO3H-catalysed rearrangements of 10 α-vinylcyclobutanones have been examined. With little acid, the β,β-dialkyl derivatives 1 were transformed into linear dienones 2 and 3; with more acid, they were converted into cyclopentenones 4 by Nazarov cyclisation of initially formed 2/3. The β-monoalkyl (including the β,γ-dialkyl) derivatives 7 rearranged only with a high acid concentration to afford the cyclopentenones 8 by 1,2-acyl migration. In the case of 7a, the cyclopentenone 8a was accompanied by the unexpected constitutional isomer 9a, which is explained by a reversible interconversion of the cyclobutanone 7a with its isomer 19 via a cyclopropane intermediate like 18. In the case of the β,β-dialkyl derivative 5, which contains an α-isobutenyl (instead of an α-vinyl) group, the acid-catalysed rearrangement product was the bicyclo[3. 1. 0]hexanone derivative 6.

Notizen: It is shown that dimethyl 7-isopropyl-5, 10-dimethylheptalene-1, 2-dicarboxylate (1) and dimethyl 5, 6, 8, 10-tetramethylheptalene-1, 2-dicarboxylate (2) can be resolved via the corresponding mono-acids and with the aid of optically active primary or secondary amines such as 1-phenylethylamine or ephedrine into the (-)-(P)- and (+)-(M)-enantiomeres, respectively. Characteristic for the (P)-chirality of the heptalene π-skeleton with C2 or pseudo-C2 symmetry are two (-)-CE's at the long wavelength region (450-300 nm) followed by at least one intense (+)-CE at wavelengths about or below 300 nm. The absolute configuration of the heptalenes was correlated with the well-established absolute configuration of (+)-(R)- and (-)-(S)-1-phenylethanol.

Notizen: Nucleosides and Nucleotides. Part 22. Synthesis of a Tridecanucleoside Dodecaphosphate Containing the Unnatural Base 2(1H)-PyrimidinoneThe tridecanucleosid dodecaphosphate d(TpTpMpCpGpTpCpApApApApTpC incorporating the modified nucleoside 1-(2′-deoxy-β-D-ribofuranosyl)-2(1H)-pyrimidione (Md, 2) was synthesized using the triester method. The intermediates were the suitably protected trimer d(TpTpM) and the pentamer d(TpTpMpCpG). The latter was condensed with the protected octamer d(TpCpApApApApTpC) to yield the desired tridecanucleotide.

Notizen: Synthesis of Macrocyclic Lactams from Ketones by Ring Enlargement ReactionA general synthesis of N-unsubstituted and N-alkyllactams of general structure III is given. Starting materials for this conversion are the aldehydes of general structure I which, by reductive amination, are converted to the corresponding amines II. Under base catalysis, the ring enlargement II→III takes place (Scheme 3).

Notizen: Selective Reactions of the Tetranortriterpenes Busseins A und BBussein A (1) was transformed to the 1′-O- and 2-O-acetyl and the 1′-O - and 2-O-chloroacetyl derivatives 3,5,4, and 6, respectively. By hydrolysis with H2SO4 in MeOH bussein J (7) was obtained from 1 and bussein K (8) from bussein B (2). Treatment of 1 with H2SO4 in H2O and tetrahydrofuran yielded 7, the acid 9, and the dilactone 16. Hydrolysis of 1 with aqueous NH3 in MeOH gave 10; at higher temperature, 12, 13, and 14 were obtained as additional products. With NaOH in aqueous MeOH 7, 10, 15, and 17 - the latter being an isomer of 15 of unknown structure - were formed from 1. Photooxidation of 1 led to 20β,21β:21β,23β-diepoxybussein A (18).

Notizen: (E)-3-(1H-Pyrrol-3-yl)-2-propenoic Acid and (E)-3-(1H-Pyrrol-3-yl)-2-propenamide from Streptomyces parvulus, Strain Tü 2480The title compounds were isolated from cultures of Streptomyces parvulus. They give a deep blue colour reaction with Ehrlich reagent. Their structures were elucidated by spectroscopy and comparison with synthetic samples. They do not show any antimicrobial activity.

Notizen: The conformational behavior of POE-bound model peptides Boc-(L-Ala)2-X-Y-(L-Ala)2-NHPOE (X - Y = L-Pro-Gly (I), Gly-L-Ile (II); NHPOE = aminopoly(oxyethylene)) as well as of the repetitive hexapeptide of elastin, Boc-L-Val-L-Ala-L-Pro-Gly-L-Val-Gly-A-NHPOE-M (III) (A = photosensitive 3-nitro-4-(bromomethyl)benzoyl group; NHPOE-M = aminopoly(oxyethylane) monomethyl ether) has been studied by means of 1H-NMR and CD spectroscopy. Compounds I and III form a β-turn with Pro and Gly in positions i + 1 and i + 2, respectively, while an aggregated state for II, has been identified. The results are in good agreement with published prediction codes giving experimental evidence for the dominance of short-range interactions to establish secondary structure in solution.

Notizen: The total synthesis of enantiomerically pure (-)-crinine (1) in 10 steps and 6% overall yield from cyclopentene oxide is reported. The key step was the rearrangement of 7 upon reaction with AgNO3 at 25°C to give cis-perhydroindolone 8 in 81% yield.

Notizen: The chemical synthesis of two dimers of the sequence 11 to 24 of adrenocorticotropin is described. The two monomers were covalently linked through their N-or C-termini, respectively, using N-acetylglutamic acid or lysine amide as spacers. Compared to the monomer, the first dimer showed moderately, the second strongly increased inhibitory potency upon steroidogenesis in isolated adrenal cells.

Notizen: The behaviour of the regioselectively generated carbocation centers at C(2) and C(6) in 1,2-trimethylenenorbornanes was investigated in order to study the occurrence or absence of a degenerate rearrangement E⇄M in the adamantane rearrangement of both 1,2-endo- (1) and 1,2-exo-trimethylenenorbornane (2) to 2-endo,6-endo-trimethylenenorbornane (3). A degenerate rearrangement E⇄M is inevitably involved inasmuch as a 1,2-trimethylenenorborn-2-yl cation E not only is formed directly as manifested by the conversions of the reactants 4 (C(2), C(3)-olefin) and 6 (C(2), C(3′)-olefin), but also indirectly (via F→E) if the leaving group at C(6) to be ionized occupies the endo-position (6-endo-alcohol 8). No degenerate rearrangement E⇄M is operative starting from reactants that lead directly to a 2,6-trimethylenenorborn-2-yl cation G; this is the case with both the ionization of the 6-exo-alcohol 10 having the leaving OH-group in a stereoelectronically favoured configuration to undergo simultaneous C(1), C(2)-bond migration (→G) as well as the protonation of the olefin 13 which is followed by same reaction pathway.

Notizen: cis, trans Isomerization of 4-Alkyl-3-vinylpiperidines by [3.3] Sigmatropic Rearrangement. Synthesis of Epivinyl Isomers of Cinchona AlkaloidsIsomerization of 4-alkyl-3-vinylpiperidines induced by formaldehyde has been studied for ethyl meroquinate and quinotoxine. The equilibration of cis- and trans-isomers occurs by involvement of a [3.3] sigmatropic rearrangement. This process permits an easy access to the trans-isomers from natural products of cis-configuration and has been used to obtain the epivinyl isomers of cinchona alkaloids.

Notizen: Conformation and Dynamics of Dimethyl [6]Paracyclophane-8,9-dicarboxylate. A 1H- and 13C-NMR StudyThe 1H- und 13C-NMR spectra of dimethyl [6]paracyclophane-8,9-dicarboxylate have been assigned and analyzed in the slow-exchange limit (-20°C) for the ring-inversion process of the methylene bridge using several 2D-NMR techniques. The vicinal 1H, 1H coupling constants of the methylene chain show a Karplus-type dependence on torsional angles. The observed values indicate that the solution conformation of 1 closely resembles that found in the crystal. No significant changes in the 1H-NMR shielding properties of the boat-shaped benzene ring were detected. The 13C chemical shifts of the methylene C-atoms can be explained without invoking ring current contributions, which are too small for unambiguous identification. A lineshape analysis for the AB⇌BA exchange system of the aromatic protons yielded ΔH≠ = 43.25 ± 0.72 kJ/mol, ΔS≠ = -51.27 ± 2.66 J/K mol, and ΔG≠(298) = 58.53 kJ/mol for the dynamic process corresponding to an inversion of the methylene bridge.

Notizen: A general approach to isosteric phosphonate analogues of ulose-l-phosphates is described. A base-catalysed chain elongation via a Michael addition of 1-deoxy-1-nitro-sugars 4, 8, and 16 to the vinylphosphonate 18 followed by hydrolysis of the nitro adducts gave the analogues of D-ribulose-1-phosphate, D-fructose-1-phosphate, and D-sedoheptulose-1,7-diphosphate 21, 23, and 27, respectively, in high yields.

Notizen: The novel 3-nitro-9-oxo-9H-xanthene- and 3-nitro-9-oxo-9H-thioxanthene-l-carboxylic acids 2a-d were prepared by intramolecular acylation of 3-aryloxy- and 3-arylthio-5-nitrophthalic anhydrides 1 (Scheme). The 3-nitro group was readily substituted by O- and S-nucleophiles and halide and azide ions to give a range of 3-substituted thioxanthone derivatives 3 with varied λmax.

Notizen: Syntheses of Dibenzo[b,e][1,4]dioxin-2,3-quinones Including the Ecklonoquinones A and B and the Isoecklonoquinones A and BOxidation of monomesyloxy-substituted pyrocatechols with MnO2 in toluene using phase-transfer conditions leads in high yield to monomesyloxy-substituted dibenzo[b,e][1,4]dioxin-2,3-quinones with loss of one mesyloxy group. In this way, ecklonoquinone A (2), ecklonoquinone B (3), isoecklonoquinone A (43), and isoecklonoquinone B (44) were prepared. Their structures are based on X-ray analyses of ecklonoquinone-A leucoacetate (45) and the mesyloxy-substituted quinone 20. The reddish-violet dibenzodioxin-diquinone 49 was prepared from an intermediate of the iso-series. The parent compound 1 has been synthesized in yields better than 50% from pyrocatechol and methyl 2,5-dioxo-2,5-dihydrobenzoate as oxidant and 2-methoxypyridin as catalyst. To rationalize the specific effect on the dimerisation step of the mesyloxy group, the intermediacy of 1,4-quinone monoacetals is proposed. This also applies to a proposed biogenetic scheme.

Notizen: Inductive charge dispersal to the α- β- and γ-positions of the solvated quinuclidinium ion has been examined by comparing the pKa and the derived inductivities ρI of several 2- 3- and 4-substituted quinuclidinium perchlorates 4, 5, and 6, respectively. The same inductivity is observed at the practically equidistant β- and γ-positions. It, therefore, appears that polar substituent effects are transmitted directly through the molecule. As expected, inductivity is considerably higher at the α-positions where through-bond and direct induction coincide. The fact that the pKa of all three series of salts correlate linearly with each other points to the common nature of these inductive electron displacements.

Notizen: Hydrogen Transfer during Decompositions of Molecular Ions of Acetals Derived from Substituted Cyclopentanones and CyclohexanonesThe isomerisation process of ethylene-acetal radical ions of low internal energy has been reinvestigated in more detail. The ring contraction of cyclohexane derivatives into methylcyclopentanes is quite general for these ions. The relative rates of [1, n] H transfers to the C free radical resulting from C—C cleavage α to the acetal group plays the most important part in the mechanism.

Notizen: Chloranil (2,3,5,6-tetrachloro-2,5-cyclohexadiene-1,4-dione; C) in deoxygenated acetonitrile shows transient absorptions which are assigned to the radical anion \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {C}^{- \kern-4pt {.}} $\end{document} and to the triplet 3C*. The absorption due to \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {C}^{- \kern-4pt {.}} $\end{document} rises ‘instantly’ during the 12 ns laser flash and then more gradually in a time of μs. This observation is explained as electron capture from neat acetonitrile by photoexcited C taking place from both its singlet and triplet states with rate constants estimated as 109 and 104 s-1 M-1, respectively.

Notizen: On triplet excitation (λ 〉 280 nm, acetone), the epoxydiene (E)-5 undergoes initial cleavage of the C(5)—O bond of the oxirane and subsequent cleavage of the C(6)—C(7) bond leading to the diradical intermediate e which reacts by recombination furnishing the cyclic compounds (E/Z)-6, (E/Z)-7,8, and 9. Alternatively, a H-shift leads to the aliphatic methyl-enol ether 10 which undergoes a photochemical [2+2]-cycloaddition to compounds 12 and 13, the main products on triplet excitation of (E)-5. On singlet excitation (λ = 254 nm, MeCN), (E)-5 undergoes cleavage to the carbene intermediates f and g. The vinyl carbene f reacts with the adjacent double bond furnishing the cyclopropene 14 as the main product. From the carbene intermediate g, the methyl-enol ether 15 arises by carbene insertion into the neighboring C—H bond. Furthermore, the diastereomer of the starting material, the epoxydiene (E)-16, and compounds 17A+B are formed via the ylide intermediate h. Finally, the cyclobutene 18 is the product of an electrocyclic reaction of the diene side chain.

Notizen: Macrocyclic Oligolactams Based on Terephthalic Acid as Ionophores with Selectivity Depending on Included Guest MoleculesMacrocyclic 20- to 60-membered oligolactam hosts exhibit ion selectivities in poly(vinyl chloride) membranes which depend on the ring size and on the substituents of the amide N-atoms. The selectivity may be changed by loading the macrocyclic host with CHCl3 as guest molecule.

Notizen: The synthesis, liquid-crystal transition temperatures, and some physical properties of a variety of substituted phenyl ethers, most of which incorporate a lateral substituent, are reported. Many of the liquid crystals described exhibit nematic phases with negative dielectric anisotropy at elevated temperatures. The relationship between the nature of the lateral substituents and the observed liquid crystal phases and transition temperatures is discussed.

Notizen: Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution III. The Monocycle [22]-Py2N4The nature and stability of complexes formed by a new 22-membered monocycle L = [22]-Py2N4 with the cations Mn+ = Cu2+, Co2+, Ni2+, Zn2+, Cd2+, Pb2+, and Ag+ have been determined in aqueous solutions (0.01M NaClO4, 25°) by pH-metry and also, for the copper system, by UV-absorption spectrophotometry. The stepwise protonation constants of the four amine functions of L were 9.1, 8.3, 7.1 and 3.7 logarithms units, respectively. No evidence was found for the protonation of the two pyridine nitrogen atoms. Mononuclear complexes MLn+ were identified in all systems investigated, but the dinuclear species M2L2n+ were only found with Cu2+ and Ag+. The logarithms of the overall stability constants for the copper and silver complexes are CuL2+, 12.9; Cu2L4+, 18.6; Agl+, 6.3; Ag2L2+, 10.9, respectively. Mononuclear hydroxy species MLOH(n-1)+ were identified in all systems except those of copper and silver. No dinuclear hydroxy complexes were detected. The complexing properties of L are compared to those of the large and less rigid bis-dien.

Notizen: Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution II. Polythiamacrotricycles and Related Monocyclic SubunitsThe stability constants of the Cu2+ and Ag+ complexes of the cylindrical macrotricycle 1a (1,7,13,19-tetraaza 4,16-dioxa 10,22,27,32-tetrathiatricyclo[17.5.5.5]tetratriacontane) have been determined by pH-metry, as well as those of the Cu2+, Co2+, Zn2+, Cd2+, Pb2+, and Ag+ complexes of the monocyclic subunit 2a (1,7-dimethyl-1,7-diaza 4,10-dithiacyclododecane), in aqueous solutions (NaClO4) at 25°. In the Cu(II) systems, equilibria were reached slowly, and the results established by pH-metry were confirmed by UV/VIS spectrophotometric studies. The tricycle 1a forms dinuclear cryptates with copper and silver, with overall stability constants log β210 (Cu2-1a)4+ = 18.5, log β21-2 (Cu2-1a(OH)2)2+ = 4.8, log β210(Ag2-1a)2+ = 23.0. Ag+ also forms a mononuclear (Ag-1a)+ complex, with log β110 = 13.1, but no mononuclear species were detected in the Cu-1a system. The absorption spectra of the bis-Cu(II) complexes of 1a and 2a in aqueous medium, MeOH and propylene carbonate (PC) are given, as well as those, in MeOH and PC, of the bis-copper complexes of the related monocycles 3 and 4 (1,7-diaza-4,10,13-trithiacyclopentadecane and 1.10-diaza 4,7,13,16-tetrathiacyclooctadecane, respectively), and tricycle 5 with two benzyl groups in the lateral chains.The complexing properties of the polyoxa- and polythia macrotricycles (Parts I and II of this series) are compared to those of other bis-chelating ligands, the bicyclic bis-tren and the monocyclic bis-dien.

Notizen: The regioselectivity of nucleophilic substitution of the nitro groups in 3,5-dinitrophthalic anhydrides and 3,5-dinitrophthalimides (Scheme) with a variety of nucleophiles (Nu-) was studied. In all cases, the 3-nitro group was selectively substituted. With excess of the same nucleophilic reagent or with other nucleophiles, the 5-nitro group could subsequently be replaced.

Notizen: Bis (2,4,6,8-cyclononatetraen-1-yl)methanesBis (2,4,6,8-cyclononatetraen-1-yl)methanes (2a-c) have been prepared by reaction of all-cis-cyclononatetraenide with 1,1-dichlorodimethyl ether as well as with carbenium ion precursors 9b and 9c. The title compounds 2 are attractive precursors of highly delocalised nonafulvenes of type 3; however, elimination experiments 2→3 failed so far.

Notizen: The reaction of anthranilamide with phosphorus pentasulfide in boiling pyridine leads to the benzodiazaphosphorine-pyridine salt 2. The structure is established by elemental analysis, 1H- 13C- 15N- 31P-NMR, and mass spectral data.

Notizen: Quinazoline Carboxylic Acids. An Easy Route to (4-Oxo-3,4-dihydroquinazolin-3-yl)-alkanoic Acids, (4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)-alkanoic Acids and their EstersA new route was found for the synthesis of (4-Oxo-3,4-dihydroquinazolin-3-yl)-alkanoic acids (8) and (4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)-alkanoic acids (6) by cyclization of the N-(2-aminobenzoyl)amino acids 5 with HCOOH or HNO2. 2H-3,1-Benzoxazine-2,4(1H)-diones (1) reacted with glycine esters to 2, which were cyclized by HNO2 to the esters 4. Ester 4 was hydrolyzed to 6 (X = CH2). Diones 1 reacted with the most common amino acids (as the ammonium salt of tertiary amine) to amino-alkanoic acids 5, which were cyclized with orthoformate to 7 or 8 depending on the reaction conditions.

Notizen: Synthesis of ErioderminThe total synthesis of eriodermin (=2,7-dichloro-4-formyl 3-hydroxy-8-methoxy-1,6-dimethyl-11H-dibenzo[b,e] [1,4]dioxepin-11-one) is described.

Notizen: Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-DiphenylheptafulveneFour 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2-5, obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’-6 to ‘endo’-9 (68-73%) and ‘exo’-6 to ‘exo’-9 (3-20%). Treatment of some of these alcohols with (CF3SO2)2O in CH2Cl2/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10-12 or 1-vinylfulvenes 13 and 14, a new class of reactive tetraenes: Both ‘endo’-9 and ‘exo’-9, having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’-6 to ‘endo’-8 afforded only the corresponding 7-membered-ring pyridinium salts 10-12 (66-79%), while ‘exo’-6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’-B and ‘endo’-6-‘endo’-8, as well as the C(1), C(7)-bond cleavage with ‘exo’-B, ‘exo’-6, and with both ‘endo’- and ‘exo’-9. Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19, respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene (23, 86%) was obtained.

Notizen: A novel antibiotic, PD 121,222, was isolated from a complex of pluramycin-like compounds containing mostly kidamycin and neopluramycin. Spectral analyses showed that this compound is the 14,16-dihydroxy analog of rubiflavin A.

Notizen: The thermophilic and anaerobic bacteria specified in the title are isolated on a 0.8 kg scale by tangential flow filtration and centrifugation from a 300-1 bioreactor. The microorganisms are stored in a freezer (-20°) and used, analogously to baker's yeast, for asymmetric reductions. Thus, ethyl 3-ketovalerate (4.3) g/1 (H2O) is converted in 40% yield to (S)-3-hydroxyvalerate (6), with an enantiomeric excess of 93% (24 h at 72°).

Notizen: 1H-Cyclopropa[b]naphthalene (10a) and 3-methyl or dimethyl derivatives have been synthesized by interception of appropriately substituted o-quinodimethanes 3 with 1-bromo-2-chlorocyclopropene 5, and subsequent dehydrohalogenation of the adducts. The o-quinodimethane derivatives 3 in turn were obtained from the diynes 7 via base-induced isomerization to bisallenes 8 and thermal electrocyclic ring closure.

Notizen: A series of penta- and hexapeptides of the structure Ac-Lxn- …-Lx1-Ly1-…-Lym-NH2 with phenylalanine or tyrosine in Lx1 and glycine or alanine in the other positions were synthesized using elastase and δ-chymotrypsin to catalyse the formation of the peptide bonds adjacent to the aromatic residue. Such oligopeptides are useful substrates for studying the secondary specificity of chymotrypsin-like proteases.

Notizen: The pseudolactones 6 and 12 were prepared in a straightforward way from methyl α-D-glucopyranoside and methyl α-D-mannopyranoside, respectively. The pseudolactone 6 reacted with tert-butyl lithioacetate to give the protected, trihydroxylated cyclohexenone carboxylate 7 (51 %). The sterically hindered, L-ribo-configurated pseudolactone 12 reacted with diethyl ethylphosphonate and dimethyl methylphosphonate to give the protected trihydroxycyclohexenones 17 (49 %) and 18 (62 %), respectively. The hydroxymethylated cyclohexenone 21 was obtained from 18 by treatment with Me2AlSPh and then formaldehyde, oxidation of the product 19, and elimination. Deprotection of 21 gave 2, identical with KD16-Ul. Esterification of 2 gave 1, identical with the title compound. Alternatively, 1 was obtained in higher yields by esterification of 21, followed by deprotection of the hydroxy groups. This synthesis gave 1 and 2 from methyl α-D-mannopyranoside in an overall yield of 18 and 20 %, respectively, confirming their absolute configuration.

Notizen: The title compound 7 and two related novel ergolines have been synthesised from (5R,8R,10R)-8-(methyl-thiomethyl)ergoline-6-carbonitrile (4). The guanidine function of 7 induces a boat conformation of ergoline-ring D, as demonstrated by a careful NMR spectroscopic analysis of 7 and its N-hydroxy congener 6. Diphenylphosphinodithioic acid has been used to convert the cyanamide function of 4 into the thiourea function at (5R,8R,10R)-8-(methylthiomethyl)ergoline-6-thiocarboxamide (5).

Notizen: Total-Synthesis of (-)-Norgestrel(-)-Norgestrel (1a) or (-)-norethindrone (1b), two active progestational ingredients of currently used contraceptives have been synthesized stereoselectively. Compound 1a has been obtained starting from m-cresol methyl ether, dimethyl malonate, and (E)-1,4-dibromo-2-butene. The steroid skeleton has been constructed using an intramolecular Diels-Alder reaction of an o-quinodimethane derivative preceeded by a photo-enolization of an appropriate methyl-substituted acetophenone derivative. Chirality has been introduced at an early stage during an ScN′ reaction (cf. Scheme 1). Compound 1b has been obtained similarly using a previously reported mixture of the enantiomerically pure constitutional isomers 18b/19b (cf. Scheme 3).

Notizen: It is shown that dimethyl heptalene-1,2-dicarboxylates undergo rearrangements at temperatures 〉 200° to yield the corresponding 1,3-dicarboxylates, which are isolated as the more stable 3,5-dicarboxylates. 2H- and 13C-labelling experiments with dimethyl 7-isopropyl-5,10-dimethylheptalene-1,2-dicarboxylate (1) which is rearranged into dimethyl 9-isopropyl-1,6-dimethylheptalene-3,5-dicarboxylates. (2) indicate that the reaction occurs by interchange of C(2) and C(3) in the heptalene skeleton of 1. Thus, the transformation of 1 into 2 represents the first thermal σ-skeletal rearrangement of heptalenes. The structures of 1 and 2 are discussed in terms of an X-ray analysis and the spectral data.

Notizen: On flash vaccum thermolysis at temperatures between 390 and 585°, the epoxyenones 1-9 and the epoxydienes 10-12 undergo various types of reactions involving C—C and/or C—O bond cleavage in the oxirane ring. Thus, the compounds 1, 4-9, 11, and 12 were transformed to the divinyl ethers 13, 20, 21, 24, 25, 29, and 38 by a reversible [1,5] homosigmatropic H-shift. On thermolysis of the epoxides 1-12, several products formed via carbonyl-ylide intermediates were also isolated. The extent of the formation of ylide products is clearly related to the conjugating ability of the functional groups neighboring the oxirane. Thus, the epoxides 3, 5, and 7-10, bearing a C(3)=C(4) bond, a 5-oxo function, a 3,4-epoxy or a 3,4-methano group, preferentially underwent reactions via a carbonyl-ylide intermediate. As a further reaction pathway, the epoxides 1-12 undergo cleavage of the C-O bonds of the oxirane, which, however, is presumably an acid-catalyzed rather than a thermal reaction.

Notizen: It is predicted by MINDO/3 calculations that the 1,5-trishomobarrelenediyl dication 4 would be as much stabilized over the bicyclo[2.2.2]octanediyl dication 3 as the monocation 7-H is energetically favored over the hypothetical 1-bicyclo[2.2.2]octyl 10-H. In spite of this, the bridgehead cations generated from the 1,5-dihalo-trishomobarrelenes 6-F, 6-Cl, 6-Br, and 6-I and from the 1,5-diol 6-OH under long-lived ion conditions were only the 5-substituted monocations 7-F, 7-Cl, 7-Br, 7-I, and 7-OH, respectively, unequivocally identified by their 1H- and 13C-NMR spectra as well as quenching products. Although there is efficient charge delocalization in 7-X, as revealed by the 13C-chemical shifts, the lack of formation of the bridgehead bridgehead dication 4 is not due to an unforeseen destabilization by the three α-annellated cyclopropyl groups. Even the 1,5-dichlorotetracyclo[3.3.2.02,4.06,8]decanes 17-Cl2 and 19-Cl2 and 1,5-dichlorotricyclo[3.2.2.02,4]nonane 12-Cl2 with only two and one α-cyclopropyl groups, respectively, gave the bridgehead monocations 18-Cl, 20-Cl, and 13-Cl, respectively.

Notizen: Methyl 2-allyl-3-oxo-2,3-dihydrothiophene-2-carboxylate (2) photocyclizes selectively to methyl 2-oxo-7-thiatricyclo[3.2.1.03,6]octane-1-carboxylate (4). In contrast, 4-thia-2-cyclohexenone 3, on irradiation, affords only low yields of dimers, cycloadducts (2-methylpropene) or RH reduction products (i-ProH).

Notizen: Investigation of the Carotenoid Composition in the Petals of a Garden Hybrid Narcissus cvv ‘Golden Harvest’The carotenoid composition of the petals of a yellow garden hybrid Daffodil is reported. As major compound (all-E)-lutein was isolated. As minor compounds phytoene, phytofluene, (all-E)-β-carotene, (9Z)-lutein, (9′Z)-lutein, (13Z)-lutein, violaxanthin, and luteoxanthin were identified. The position of the (Z)-double bond of the different isomers of lutein could be proved by 1H-NMR spectroscopy.

Notizen: The isotopic exchange between hydrogen and methane over Ni catalyst has been studied as a function of temperature, isotopic substitution, and ratio of hydrogen to methane. The experimental results can be described by means of a model in which methane is adsorbed either as methyl or as methylene. The adsorbed species undergo one or several exchanges. The four required parameters are adjusted to the experimental results. The exchange of partially deuterated methane with H2 or D2 allowed us to study the isotopic effect on the adsorption and the exchange processes.

Notizen: The didehydro[n]annulenes 1 (n = 14), 2 (n = 18), and 3 (n = 22) are oxidized to radical cations. Reduction of the title compounds leads to radical anions and, in the case of 2 and 3, to radical trianions. The hyperfine data of the paramagnetic derivatives are rationalized in terms of the occupation of n-membered (n = 14, 18, 22) π-perimeter MO's (HOMO, LUMO, NLUMO). The contact-ion pairs of the radical anions show unexpectedly large alkali-metal coupling constants.

Notizen: Hormosirene ((-)-1; (1R,2R)-1-((1E,3Z)-1,3-hexadienyl)-2-vinylcyclopropane) is the specific sex attractant of several brown algae of the Australian shelf, while dictyopterene A ((+)-2; (1R, 2R)-1-((1E)-1-hexenyl)-2-vinylcyclopropane) is found as a minor constituent of the pheromone bouquets. The asymmetric synthesis of the two hydrocarbons is performed by resolution of the amides (-)-5 and (+)-5a obtained from (-)-(R)-2-phenylglycinol and racemic trans-vinylcyclopropanecarboxylic acid (rac-4) on silica gel. Both diastereoisomers are obtained optically pure. They are converted by stereoselective Wittig olefination into the title compounds. Compound (-)-1 is the active mating pheromone of the reproductive system of the seaweed Xiphophora chondrophylla as established by biological-activity assays.

Notizen: Multiple chlorinations and arylations at the tertiary positions of adamantane are promoted by FeCl3-doped K10 montmorillonite in CCl4 or in aromatic solvents. The process, remarkably easy to implement, can be tailored to selective formation of monosubstituted 1-adamantyl derivatives or 1,3-disubstituted adamantanes. The process achieves alkylation at the meta- and para-positions of toluene leading to a purely statistical distribution and displays no substrate specificity in competition experiments between toluene and benzene.

Notizen: Variously substituted 4,5-dihydro-5-vinylisoxazoles, obtained by regio- and stereospecific cycloaddition of nitrile oxides to dienes, undergo smooth OsO4-catalyzed cis-hydroxylation to give amino-polyol precursors. The reaction is ‘anti’-selective, the diastereoisomeric ratios ranging from 73:27 up to ≥ 99:1. Thus, the cycloaddition/osmylation sequence allows the control of the relative configuration of up to four contiguous asymmetric centers. A sulfoxide-mediated approach to enantiomerically pure compounds is also described.

Notizen: Two synthetic approaches to the novel C10H16 hydrocarbon tricyclo[4.4.0.03,9]decane (1; 2-homotwistbrendane), one of the 19 members of the adamantaneland, and its Lewis-acid-catalyzed rearrangement are described. One route starts from tricyclo[4.3.0.03,8]nonan-2-one (2; 2-twistbrendanone). The missing tenth C-atom is introduced by ring enlargement (Tiffeneau-Demjanov method). Starting from methyl 8,9,10-trinorborn-5-ene-2-endo-carboxylate (8), ring enlargement by one C-atom, regio- and stereoselective introduction of a C1 unit to a 2-endo,6-endo-disubstituted bicyclo[3.2.1]octane, and ring closure by acyloin condensation are the key steps in the second approach.

Notizen: The phenolic compounds of the fern Dryopteris aitoniana were analyzed by improved methods avoiding alcaline reagents and contact with unbuffered SiO2, which can cause deterioration. We confirmed the presence of five of the formerly (1971) reported six compounds, while the sixth, formerly incorrectly assumed to be aspidin (based on a spot in TLC), has now been isolated as cristals (TR-1579). It has the empirical formula C27H52O2, but its structure is still unknown. Five other compounds were isolated in pure form, tetra-albaspidin BBBB (25-BBBB) a known but rare phloroglucinol, and four new compounds: penta-albaspidin BBBBB (37-BBBBB), hexa-albaspidin BBBBBB (38-BBBBBB), tetraflavaspidic acid BBBB (26-BBBB) and hexaflavaspidic acid BBBBBB (39-BBBBBB). The structures were established by degradation NMR and partly by field-desorption and fast-atom-bombardment (FAB) mass spectra. The oligoflavaspidic acids are very unstable compounds, deteriorating during isolation procedures using the older ‘standard method’.

Notizen: Surface Modification of Carbon Electrodes by Polymers Consisting of Epoxy Resins and a Derivative of Vitamin B12A derivative of vitamin B12 containing a 3,5-diaminobenzoyl group in the c side-chain has been synthesized. It was used as the amine component in the formation of an optically active cross-linked epoxy-polymer. Surface modification of carbon electrodes (basal plane graphite and carbon felt) has been achieved by impregnating them with solutions of the monomers followed by thermal curing at 120°C. Electrochemical responses of the Co(II)/Co(I) redox system from sub-mono to multilayer coverages have been observed. The polymer exhibits catalytic activities typical for monomeric vitamin B12 as shown by spectroscopic and electrochemical techniques. Polymermodified electrodes with large specific surfaces have been used in organic electrosynthesis, i.e. the exclusive formation of valeronitrile by reductive cross-coupling of ethyl iodide and acrylonitrile.

Notizen: Asymmetric Michael-Additions. Stereoselective Alkylation of Chiral, Non-racemic Enolates by Nitroolefins. Preparation of Enantiomerically Pure γ-Aminobutyric and Succinic Acid DerivativesChiral, non-racemic lithium enolates (E,F,G) of 1,3-dioxolan-4-ones, methyl 1,3-oxazolidin-4-carboxylates, methyl 1,3-oxazolin-4-carboxylates, 1,3-oxazolidin-5-ones, and 1,3-imidazolidin-4-ones derived from (S)-lactic acid (2a), (S)-mandelic acid (2b), and (S)-malic acid (2c), or from (S)-alanine (10), (S)-proline (11), (S)-serine (12), and (S)-threonine (13), are added to nitroolefins. Michael adducts (3-9, 14-18) are formed (40-80%) with selectivities generally above 90% ds of one of the four possible stereoisomers. Conversions of these nitroalkylated products furnish the α-branched α-hydroxysuccinic acids 28 and 29, the α-hydroxy-γ-amino acid 25, the α,γ-di-amino acid 32, the substituted γ-lactames 19-22, and the pyrrolidine 23. The relative and absolute configuration of the products from dioxolanones and nitropropene are derived by chemical correlation and NOE measurements indicating that the steric course of reaction is to be specified as 1k, ul-1,3. The mechanism is discussed.

Notizen: A new hydroquinone diterpenoid was isolated from Clerodendrum uncinatum SCHINZ (Verbenaceae) by flash chromatography on silica gel. The structure was established as 7,11-dihydroxy-3,4,9,11b-tetramethyl-1,2,8,9,11b-pentahydrophenanthro[3,2-b]furan-6(2H)-one by spectroscopic methods and X-ray analysis. The diterpene was strongly fungitoxic to spores of Cladosporium cucumerinum.

Notizen: Pure L-biopterin was obtained in 42% yield by the condensation of 5-deoxy-L-arabinose-phenylhydrazone-triacetate with 4-hydroxy-2,5,6-triaminopyrimidine, followed by iodine oxidation of the formed tetrahydropterin derivative to 1′,2′-O-diacetyl-L-biopterin. Deacetylation was carried out with NH4OH.

Notizen: Furancarboxylic Acids in Cattle UrineThe urine of cattle contains large amounts of furancarboxylic acids. The same acids were isolated from rats after feeding with methyl esters of the so-called F-acids. Since the F-acids were not detected in cattle-food, they must be produced somewhere in the body of cattle.

Notizen: On the Interaction between Lithium Enolates and Secondary Amines in Solution and in the CrystalWhen lithium derivatives generated by lithium diisopropylamide (LDA) are quenched with a D+ source (large excess of ROD), there is frequently only partial deuterium incorporation (non-stoichiometric effect, Scheme 1). Experiments with tert-butyl 2-methylpropionate (1) and its deuterated derivative (2-D)-1 and LDA indicate that the lack of deuteration is not caused by an isotope effect (Scheme 2). A H-bonded complex between the amine (R2NH) and the Li-derivative was envisioned as being responsible for the observed effects. Some crystalline Li-enolate solvates with secondary amines were isolated, and gave rise to only partially deuterated products upon quenching with AcOD/CD3OD (Table 1). Enolates containing the Li-chelating diamine N,N,N′-trimethylethylenediamine (TriMEDA) turned out to be especially suitable for the isolation of single crystals. Thus, two X-ray crystal-structure analyses were undertaken to obtain detailed information about the geometry and bonding in such complexes. The structures of the dimeric N,N-dimethyl-propionamide lithium (Z)-enolate ([2 (Z)-4·2 TriMEDA]; R value 0,049, see Eqn. 2, Figs. 2, 4 and (5) and of the dimeric pinacolone lithium enolate ([2 6·2 TriMEDA]; R value 0,082, see Eqn. 3 and Figs. 3, and 6) were determined. In both centrosymmetric dimeric structures there is a Li-O-Li-O four-membered ring and a H-bridge between TriMEDA and the enolate moiety. In the case of the amide enolate (Z)-4·TriMEDA the bridge points from the amine N-atom to the pyramidalized, enamine-type N-atom of the enolate (N … N distance 3.173(1) Å, H … N distance 2.21 (Å). In the complex 6·TriMEDA of the ketone enolate there is a H-bridge pointing from the amine N-atom to the enolate double bond (N … Cterminal distance 3.45(1) Å, H … Cterminal distance 2.62 Å; see Table 3). The geometries of the TriMEDA-Li fragments in the two structures are compared with those of standard TMEDA-Li moieties (Table 2). The two structures are discussed and interpreted using the structure correlation principle; the intermolecular interactions seen in these complexes are considered as points on the reaction coordinates of conversions between the species involved. Thus, they resemble the approach of a secondary amine in the protonation of an enamine N-atom and of an enolate C-atom. At the same time, they represent the final stages of deprotonation of an enammonium ion and of a ketone. The N—H … N bridge in 4 is in agreement with experimental observations and with calculations by Müller, indicating that enamines are kinetically protonated on the N-atom. From the pinacolone enolate structures which are now known, (a) possible transition states of deprotonation of carbonyl compounds by Li-amide bases (Figs. 7 and 8), (b) the hypothetical structure of a (i-Pr)2NH/ethyl tert-butyl ketone (E)-enolate (Fig. 8b and Fig. in Footnote 18), c) the approach of the two trigonal centers in an aldol-addition reaction, and the d) trajectory of electrophile attack on a double bond (Fig. 9) are deduced using simple molecular modeling without energy minimization. A comparison with and a discussion of the experimental and theoretical investigations about these same processes by Ireland, Corey, Dauben, Williard, and Houk are given. Finally, we believe that the H-bonding discovered in the crystal structures (Z)-4·TriMEDA and 6·TriMEDA is relevant to what Cram once called the ‘conducted-tour’ mechanism of base-catalyzed racemizations.