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Notes: Abstract 160, 162Tm nuclei have been reinvestigated at high spins by128, 130Te(37Cl, 5n) reactions, respectively. In the yrast bands of both nuclei the crossing frequencies correspond to the second neutron backbending (BC). The same is true for the side bands in162Tm but not in160Tm where the first neutron backbending(AB) is observed.

Notes: Triaziridines. Synthesis of cis-2,3-Diisopropyltriaziridine-1-carboxylic EstersIrradiation of the (Z)-azimines 1a, b in Et2O with a Hg high pressure lamp through Corex yielded (besides 30% of the previously described trans-triaziridines 3a, b) 15% of the new cis-triaziridines 4a, b. The same irradiation of the (E)-azimines 2a, b afforded only 15-18% of 3a, b but 20-23% of 4a, b. Thus, these azimine photocyclizations show some stereospecificity. The triaziridines 3a, b and 4a, b formed in this way were always accompanied by the same three types of by-products, namely 10-15% of the ‘triazones’ 5a, b, 11-20% of the carbamic esters 6a, b, and 5-10% of the ether/nitrene insertion products 7a, b. The constitution and configuration of the new cis-triaziridines 4 followed from their spectral properties. Of particular interest are the symmetry properties of 4 derived from the 1H-, 13C-, and 15N-NMR spectra: The stereoisomers 3 and 4 differ only in that the isochronicity of the two constitutionally equivalent molecular halves is temperature dependent in 3 but independent in 4. Both triaziridines 3 and 4 exhibit the IR CO band at (for carbamates) remarkably high frequency. The results confirm that the alkyl-substituted N-atoms of triaziridines are pyramidally stable, that the corresponding acyl-substituted N-atoms (N(1)) are also pyramidal, but can invert more readily, and that rotation around the N(1), C(=O) bond is rapid. Thus, there can be only little amide-type delocalization between a triaziridine N-atom and an acyl substituent of the carbamate type attached to it.

Notes: Synthesis of Some 8-Substituted 2-Methyl-1,2,3,4-tetrahydroisoquinolinesA general route to 8-substituted tetrahydroisoquinolines is exemplified by the preparation of the 2-methyl-1,2,3,4-tetrahydroisoquinolin-8-ol (11), the -8-carbaldehyde oxime (12) and the -8-carbonitrile (13). It involves the conversion of isoquinoline (1) by partially modified Steps 1, 2, 3, and 5 (see the Scheme) into the 5-bromo-8-nitro derivative 5, reduction of the latter to the 8-amino derivative 8 and replacement of the NH2-group with an appropriate substituent by a Sandmeyer-like reaction. The selective reductions of the N-containing ring in 6 (Steps 5, 6, and 8) and of the NO2-group in 5 (Steps 4 and 7) were also studied.

Notes: Triaziridines. Ring Openings of TriaziridinesEleven triaziridine derivatives were heated at 60° in CDCl3 to obtain information on the tendency towards, resp. the resistance to, ring opening of the N3-homocycle by thermolysis. Among these triaziridines, there are three which contain, as one of the substituents, a methoxycarbonyl group (ester derivatives 1, 5 and 16), three a methyl group (methyl derivatives 18, 24, and 26), three an H-atom (14, 27, and 30), and two a negative charge (31 and 32). The other two substituents in each of these four classes of triaziridines are trans-located i-Pr groups (1, 18, 27, and 31), cis-located i-Pr groups (5, 24, 14, and 32), and a 1,3-cis-cyclopentylidene group (16, 26, and 30). As major products these mild thermolyses, we isolated : from the trans-ester 1 and from the annellated ester derivative 16, the 1-acyl-azimines 2 and 17, respectively, from the cis-ester 5, the 3-acyl-triazene 4, from the trans-methyl derivative 18, the (E)-diazene 19, and hexamine 21, from the cis-methyl derivative 24 the 2-methylazimine 25, both from the trans- and cis-H-derivatives 27, and 14, respectively, the H- triazene 13 and, finally, both from the trans-and cis-anion 31 and 32, respectively - after protonation the H-triazene 13 and - after methylation - the methyl-triazene 33. The same thermolysis of the annellated methyl and H-derivatives 26 and 30, respestively, resulted only in decomposition.These results can be uniformly interpreted with a primary opening of the triaziridine ring by rupture of one of the two types of N—N bonds lending to azimines or triazenide anions. Some of the azimines were isolable, namely 2, 17, and 25, and one was spectroscopically observable as an intermediate, namely 11 on the way to the triazene 4. The other azimines are plausible intermediates to the isolated products, namely 15 on the way to 13, and 22 on the way to 19 and 21. The triazenide anion 28 is the evident intermediate on the way to 13 or to 33. The annellated azimines are assumed not be formed from 26 and 30, or then to be be decomposed under the conditions of their formation. We conclude that the triaziridine derivatives 1, 16, and 18 underwent thermal ring opening between N(1) and N(2), while the derivatives 5, 14, 24, 27, 31, and 32 were ruptured between N(2) and N(3); no conclusion was possible on the ring opening of the derivatives 26 and 30.The predominant formation of the (Z)-azimine 2 from the trans-triaziridine 1, and of the (E)-isomer 3 - among the two azimines - from the cis-triaziridine 5 suggests a stereospecificity in the triaziridine ring openings. This would, however, not be expected to be observable in the products from the other triaziridines, since both N—N bonds of the azimine 25 and of the anion 28 probably rotate rapidly and since the secondary trans formations of the other primary products are not able to retain configurational information.

Notes: Stable Pyramidal configurations at the Nitrogen Atoms of Dialkyl-and Trialkyl-triaziridinesStereochemical features of the recently synthesized nine samples of di- and trialkyl-triaziridines, namely the 1,3-cyclopentylen-(series a) and the two stereoisomers of the diisopropyl derivatives (series b and c), containing as the third substituent an H-atom (2), a CH3 group (3)or a CH2OH group (4), were elaborated on the basis of the 1H-, 13C-, and 15N-NMR spectra. The three N-atoms of the saturated N3-homocycle were found to be stable to pyramidal inversion in all cases. According to their NMR spectra, 2-4 of the series a and b possess twofold symmetry (Cs), while 2-4 of series c are asymmetric. Thus, series c has the trans-configuration at N(2)/N(3) and, consequently, the cis-configuration at N(1)/N(2), while series a and b have the cis-configuration at N(2)/N(3) and -since the all-cis-arrangement is excluded-the trans-configuration at N(1)/N(2). The asymmetry of the trans-configurated 2c turned into twofold symmetry (C2), when a little CF3COOH was added. The 1H- and 13C-NMR data of series b and c of our alkyl-triaziridines exhibit a shielding effect, according to which there are two types of i-Pr groups, i-Pr(a) and i-Pr(b). They differ in the NMR signals of the H- and the C-atoms of their CH groups: the H-atoms of i-Pr(a) are more deshielded by 0.75-1.111 ppm and its C-atoms are more shielded by 10.0-160.0 ppm as compared to the corresponding atoms of i-Pr(b). i-Pr(a) is cis (on the N3-homocycle) to a large substituent (such as i-Pr, Me, CH2OH) and to a lone pair, while i-Pr(b)is cis only to a small (H) or to no substituent and to one or two lone pairs. An analogous effect appears in the NMR signals of the CH3 and CH2OH groups at N(1) of 3 and 4 in the series b and c.

Notes: 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.

Notes: A 6-step synthesis of (±)-grandisol (1) is presented, which involves dichloroketene addition to 3-methyl-3-butenyl acetate (4), reductive dechlorination of the adduct 6 to the ketone 7 and saponification to 8, aldolization of 7 or 8 with acetone and cyclization to the bicyclic ketone 9, Wolff-kishner, reduction to 14, and finally ring opening to 1. Since 9 is a known intermediate of the synthesis of (±)-lineatin (2), the latter can now be obtained in 6 steps.

Notes: Formal Total Synthesis of (±)-Isocomen by Application of the α-Alkinon CyclizationA total synthesis of the racemic form of the sesquiterpene isocomene (A) was accomplished by application of the cyclopentenone anellation B→D (Scheme 1) which includes the α-alkynone cyclization C→D, a gas-phase flow thermolytic process. Starting with the known product 2 (Scheme 3) of the anellation B→D, the elaboration of ring C of A proceeded in 9 steps to the α-alkynone 16 (Scheme 5) which was cyclized at 540° selectively to give the angularly fused triquinane 4 (77%). A two-step procedure then led to 5 (Scheme 6), a last but one intermediate in a known total synthesis of (±)-A. The conversion of 16 to 4 also demonstrated the compatibility of an acetoxy function with the anellation sequence B→D.

Notes: Synthesis of Racemic Aminosugar Lactones: xylo- and lyxo-2,3-Diacetylamino-5-acetoxypentan-4-olide and -2,3,5-Triacetylaminopentan-4-olideStarting with 5-hydroxy-2-penten-4-olide (1), the tricyclic intermediate 4 was prepared via the chloride 2, the acyl azide 3, and an intramolecular nitrene addition (Scheme 3). Azide ion opened the aziridine ring in 4 at C(α) to give 5, which was transformed via 7 into one of the title compounds, the triacetylated diamino-hydroxy-lactone 13 (Scheme 4). An alternative conversion of 4 into 13 involved the synthesis of the N-acetylaziridine 10, the opening of the 3-ring of 10 with N3- to form 12, and a final reductive acetylation (Scheme 5). The third N-substituent was introduced at C(δ) of 13 by the following sequence: hydrolysis of the AcO group (→14), mesylation (→15), substitution by N3- (→ 16), and reductive acetylation to yield the other title compound, the triacetylated triaminolactone 17 (Scheme 6). Since the ring opening of aziridines by nucleophiles occurs by inversion, the primary products 5a and 12a of the N3- reactions as well as the substances derived from them, i.e. 6a, 7a, and 13a-17a, have the xylo-configuration (a-series). Under some of the reaction conditions, the primary xylo-products suffered a partial epimerization at C(α) to yield mixtures containing the corresponding lyxo-products (b-series): The equilibrium between the xylo- and lyxo-isomers was estimated for 5a/5b=1:3, 12a/12b=5:2, 13a/13b=3:1, and 16a/16b=2:1. Since the stereoisomers of the a- and the b-series were always separable, the other lyxo-products, i.e. 6b, 7b, could be prepared from 5b and 12b.

Notes: Short Total Syntheses of (±)-Sativene and (±)-cis-SativenediolOur approach to (±)-sativene (7) and (±)-cis-sdtivenediol (9) involves: (a) reaction of 3-methylbutanoyl chloride with Et3N/cyclopentadiene to give the endo-isopropyl-ketone 1 (here improved to 71%), (b) NBS bromination of 1 to a 5:1 mixture (87%) of the bromo-ketones 2 and 3, (c) NFD-reaction sequence initiated by the attack of 1,2-butadienyl titanate (complex of 15, obtained from 2-butine) on 2/3 to afford 52% of the brexenone derivative 4 (along with 8% of its epimer 16), (d) addition of dibromomethane to 4 forming 63% of the diene-alcohol 5 (along with 13% of the diene-carbaldehyde 38), and (e) carbenoid ring-expansion with MeLi applied to 5 resulting in 41% the diene-ketone 6 (along with 15% of a 1:3 mixture of the diene-ketones 32 and 33). Wolff-Kishner reduction of 6 led to 81% of (±)-sativene (7), when enough O2 was present, but to 97% of the diene 8 in the strict absence of O2. (±)-cis-Sativenediol (9) was obrained (86%) by OsO4 hydroxylation of 8. The brexenone derivatives 4 and 16 (6:1, 50%) were also produced when the NFD-reaction sequence was applied to the isomeric bromo-ketone mixture 13/13 (1:3). The latter was obtained by NBS bromination of 10, which in turn was available by base epimerization of 1, followed by destructive removal of unreacted 1 by repeated gas-flow thermolysis. An analogous (less convenient) route to (±)-sativene (7) passed through a series of dihydro compounds (the ene series) it started with the methylidene-ketone 36, which was the product (97%) of a partial hydrogenation of 4. Addition of dibromomethane to 36 led t 62% of the methylidene-alcohol 39 (along with a little tetracyclic ether 40). Carbenoid ring expansion of 39 with MeLi afforded ca. 42% of the methylidene-ketone 41 (along with 7% of the methylidene-ketone 43 or, under slightly different condition, along with 9% of the methylidene-ketone 42 and 10% of the methylidene-carabaldehyde 44). The methylidene-alcohol 39 and the methylidene-ketone 43 were also obtained by partial hydrogenation of 5 and 33, respectively. Wolff-Kisher reduction converted 41 into (±)-sativene (7 99%); the same conditons applied to 42 afforded only ca. 8% 7 (along with three other hydrocarbons, one of them (ca. 21%) probably being (±)-copacamphene (45)). In the diene series, the two succeeding reactions (4→5 and 5→6) competed with the same side reaction, a rearrangement leading to the brendene-aldehyde 38. In the ene series, the corresponding dihydro-by-product 44 was found in the reacton 39→41, but not during 36→39. These side reactons could largely be suppressed by keeping the reaction temperature low. An explanation is proposed.