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Notes: Since we found certain structural features of triaziridine (1) obtained by MNDO calculations to be in qualitative agreement with those derived earlier from ab initio calculations, we used the MNDO method to derive properties of formyltriaziridine (2) and 1-formyl-2,3-diisopropyltriaziridine (3) as models for the preparatively known 2,3-dialkyl-triaziridine-1-carboxylates 4 and 5. The main results are: (a) The triaziridine N-atoms with H, alkyl, or formyl as substituents (see 2 and 3) are pyramidal. N(1) carrying the formyl group is flatter than N(2) and N(3) with H or alkyl substitent. Bond lengths and angles at N(2) and N(3) are almost identical with those calculated for the N-atoms of 1. (b) The MNDO inversion barriers at the H-substituted N(2) and N(3) of 2 are higher than those at the formyl-substituted N(1), but similar to the ab initio barriers at the N-atoms of 1. (c) The MNDO inversion barriers at N(1) of 2 and 3 are 53 to 92 kJ/mol, whereas the rotation barriers around the N(1)-C(4) bond are 7 to 23 kJ/mol; thus, the previously observed dynamic NMR phenomena in trans-2,3-diisopropyltriaziridine-carboxylates (5) can now be assigned to the slowing down of N(1) inversion rather than N(1)-C(4) rotation.

Notes: Ab initio calculations of structure, properties, and tautomerization reactions of triazene (1) at the HF/3-21G//3-21G, HF/6-31G*//6-31G*, HF/6-31G**//6-31G*, and MP2/6-31G*//6-31G* levels led to the following conclusions and predictions: (a) Calculations of the ground-state structure of (E)- and (Z)-triazene (1a and 1b, respectively) at various levels of theory show for both isomers C1 geometry with a rather flat pyramidal configuration at N(3), and small energy differences (0.2-7.2 kJ/mol) between C1 and Cs geometry, i.e. inversion at N(3) is a quasi-free process. With all levels of calculations, 1a is found to be of lower energy than 1b by 23-30 kJ/mol. (b) Comparison of vibrational frequencies of (E)-diazene (3) calculated at the HF/3-21G level with experimental values reveals that HF/3-21G calculations are reliable for the prediction of vibrational frequencies of polyaza compounds, if corrected by a factor of 0.91. On this basis, the harmonic vibrational frequencies of 1a and 1b were predicted. (c) For the rotation around the N(2) - N(3) bond of 1a two conceivable transition states, 5a (syn) and 5b (anti) were located (HF/3-21G). The energy differences between 5a or 5b, and 1a are in the order of magnitude of 50-56kJ/mol and show a slight preference for the anti-mode, i.e. energy barriers for the N(2) - N(3) rotation are obtained comparable to those observed experimentally with substituted (E)-triazenes (4). (d) Protonation of 1a at N(1), N(2), or N(3) leads to 6a, 6b, and 6c, respectively -the last one resembling an intermediate of formation of 1 from hydrogendiazonium ion (7) and ammonia (8). Energetically, the conjugate acids of 1a follow the sequence 6a 〈 6c 〈 6b. (e) The preference of N(1) protonation of 1a is also reflected in the relatively high gain of energy in the formation of H-bonded dimers of 1a with H-bonds from N(3) - H to N(1). Calculations of three different H-bonded dimers 9a-c of 1a with the 3-21G basis show that an eight-membered cyclic dimer 9c with two H-bonds from N(3)—H to N(1) is energetically most favoured (67.5 kJ/mol below two separate molecules of 1a). This dimer might well be the starting situation of double intermolecular H-transfer leading to an automeric dimer 9c via an energetically low-lying transition state 12, thus offering a low-energy pathway for the known easy tautomerization of mono- or disubstituted (E)-triazenes. For 9c⇄9c, the activation energy including correction for polarization and correlation effects as well as for vibration zero-point energy is estimated to be ca. 54kJ/mol. (f) A six-membered cyclic dimer 9b of 1a with two H-bonds from N(3)—H to N(2) might be involved for double H-transfer via a transition state 11 to a dimer 10 of (E, Z)-azimine (2). This process, however, turns out to be energetically highly disfavoured (estimated energy barrier for 9b→10: 232 kJ/mol) in contrast to the reverse reaction (10→9b via 11: 4 kJ/mol). This leads to the prediction that azimines bearing an H-atom at N(2) might be kinetically too instable for isolation, being, instead, easily tautomerized to triazenes by bimolecular H-transfer.

Notes: The 4-hydrazinobenzyl alcohol (3 was prepared (58%)) by diiobutylaluminiumhydride reduction of methyl 4-hydrazinobenzoate (4), whereas LiA1H4 or LiBh4 reduction of4 proceeded further to yield (via intermediate 3) (4-tolyl)hydrazine (5). The alcohol 3 was stable under O2-free conditions and exhibited no tendency to eliminate H2O, neither thermally nor with H+ catalysis. Oxidation of 3 with SeO2 yielded 4-(hydroxymethyl)benzine-diazonium ion (8), identified by its azo coupling product 9 with 2-naphthol. Condensation of 3 with 1-benzyl 5-Hydrogen N-(benzyloxycarbonyl)-L-glutamate (10) in presence of dicyclohexylcarbodiimide afforded 81% of N2-(benzyloxycarbonyl)-L- glutamic acid 1-(benzyl-ester) 5-{2-[4-(hydroxymethyl)phenyl]hydrazide} (11) which upon controlled hydrogenolysis (quinoline-sulfur-poisoned Pd/C catalyst) gave 82% of L-Glutamic acid 5-{2-[4-(hydroxymethyl)phenyl] hydrazide} (1), i. e. agaritine, a metabolite of Agaricus bisporus. Without poisoning of the catalyst, hydrogenolysis of (11) yielded L-glutamic acid 5-[2-(4-tolyl)hydrazide] (12).

Notes: Kristallstruktur von cis-(4′-Methyl-N,N,O)-azoxybenzolDurch Röntgen-Strukturanalyse der Titelverbindung 3d konnte die Stellung des Sauerstoffatoms eindeutig festgelegt werden. Dies impliziert zugleich eine sichere Strukturzuordnung für die stellungsisomere cis-Azoxyverbindung 4d. Frühere Strukturzuordnungen [8] für 3d und 4d werden damit zwar bestätigt, doch zeigt ein Vergleich der 1H-NMR.-Spektren aller vier isomeren 4-Methyl-azoxybenzole 1d bis 4d in Deuteriotrichlormethan, dass die früheren Zuordnungsargumente aufgrund der relativen Lage der Methylsignale in den 1H-NMR.-Spektren in Benzol unzureichend waren. Auch Verwendung von Tris (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octandionato)europium (Eu(fod)3) als Verschiebungsreagens für die 1H-NMR.-Spektren von Gemischen von 3d und 4d erlaubt, im Unterschied zu der Situation bei Gemischen der stellungsisomeren trans-4-Methyl-azoxybenzole 1d und 2d [18], keine eindeutige Zuordnung der Signale beider cis-Stellungsisomeren. Dagegen lässt sich das 1H-NMR.-Spektrum von reinem 3d in Deuteriotrichlormethan nach Zusatz von Eu (fod)3 im Einklang mit dem Ergebnis der Röntgen-Strukturanalyse interpretieren.Die Röntgen-Strukturanalyse von 3d ist die erste einer unsymmetrisch substituierten und zugleich die erste einer cis-konfigurierten aromatischen Azoxyverbindung. Das Resultat der Analyse ist in den Fig. 1, 2 und 3 dargestellt. Bindungslängen und Winkel der Azoxygruppierung und entsprechende Werte anderer aromatisch substituierter Azo- und Azoxystrukturen, für die Röntgen-Strukturanalysen bekannt sind, finden sich in Tabelle 2 zu Vergleichszwecken.

Notes: Triaziridines. II. First Examples: Alkyl 2,3-Dialkyl-triaziridine-1-carboxylatesThe first examples of substituted triaziridines 2 are described; they carry an alkoxycarbonyl and two alkyl groups (as in 4). The preparation of these novel threemembered nitrogen homocycles was achieved by photolysis of 1-alkoxycarbonylazimines 3c. In this way, methyl 2, 3-(cis-1, 3-cyclopentylene)triaziridine-1-carboxylate (6a), methyl trans-2, 3-diisopropyl-triaziridine- 1 -carboxylate (8a) and their ethyl ester analogues 6b and 8b were obtained in 50, 18, 65 and 21 % yield, respectively. The structure of the triaziridines 6 and 8 was deduced from their spectroscopic properties which reveal several interesting features: 1) N (2) and N (3), carrying alkyl groups, are pyramidal and invert slowly; 2) the isopropyl groups of 8 are situated trans to each other on the three-membered ring, whereas the two alkyl groups of 6 are cis as forced by the C-ring system; 3) N (1) is also pyramidal, despite its «amidic» nature; it inverts with an activation energy of 62 (± 4) kJ/mol; 4) the alkoxycarbonyl, group does not conjugate with N (1) and rotates rapidly.The triaziridines 6 and 8 are thermally labile, isomerizing slowly at room temperature into the corresponding azimines 5 and 7 by cleavage of one of the bonds to N (1 ). The velocity of this ring opening reaction is almost the same for 6 and 8, so that a dependence on the relative configuration at N (2) and N (3) is not evident. The Arrhenius activation energy for the isornerization of 6a to the corresponding azimine 5a and the enthalpy difference between 6a and 5a were both determined as 100 (± 4) kJ/mol.The photolysis of 1-alkoxycarbonyl-2, 3-diisopropyl-azimines (7) in diethyl ether was accompanied by a side reaction leading to methyl and ethyl N-(1-ethoxyethyl)carbamate (9a and 9b, resp.), presumably by insertion of the alkoxycarbonylnitrene, generated by photofragmentation of the azimines, into the ethereal solvent.

Notes: Azimines IV. Kinetics and Mechanism of the Thermal Stereoisomerization of 2,3-Diaryl-1-phthalimido-azimines1)Mixtures of (1E, 2Z)- and (1Z, 2E)-2-phenyl-1-phthalimido-3-p-tolyl-azimine (3a and 3b, resp.) and (1E, 2Z)- and (1Z, 2E)-3-phenyl-1-phthalimido-2-p-tolylazimine (4a and 4b, resp.) were obtained by the addition of oxidatively generated phthalimido-nitrene (6) to (E)- and (Z)-4-methyl-azobenzene (7a and 7b, resp.). Whereas complete separation of the 4 isomers 3a, 3b, 4a and 4b was not possible, partial separation by chromatography and crystallization led to 5 differently composed mixtures of azimine isomers. The spectroscopic properties of these mixtures (UV., 1H-NMR.) were used to determine the ratios of isomers in the mixtures, and served as a tool for the assignment of constitution and configuration to those isomers which were dominant in each of these mixtures, respectively.Investigation of the isomerization of the azimines 3a, 3b, 4a and 4b within the 5 mixtures at various concentrations by 1H-NMR.-spectroscopy at room temperature revealed that only stereoisomers are interconverted (3a ⇄ 3b; 4a ⇄ 4b) and that the (1E, 2Z) ⇄ (1Z, 2E) stereoisomerization is a unimolecular reaction. These observations exclude an isomerization mechanism via an intermediate 1-phthalimido-triaziridine (2) or via dimerization of 1-phthalimido-azimines (1), respectively. The 3-p-tolyl substituted stereoisomers 3a and 3b isomerized slightly slower than the 3-phenyl substituted ones 4a and 4b, an effect which is consistent with the assumption that the rate determining step of the interconversion of (1E, 2Z)- and (1Z, 2E)-1-phthalimido-azimines (1a ⇄ 1b) is the stereoisomerization of the stereogenic center at N(2), N(3), either by inversion of N(3) or by rotation around the N(2), N(3) bond. The total isomerization process is assumed to occur via the thermodynamically less stable (1Z, 2Z)- and (1E, 2E)-isomers 1c and 1d, respectively, as intermediates in undetectably low concentrations which stay in rapidly established equilibria with the observed, thermodynamically more stable (1E, 2Z)- and (1Z, 2E)-isomers 1a and 1b, respectively.At higher temperatures, the azimines 3 and 4 are transformed into N-phenyl-N,N′-phthaloyl-N′-p-tolyl-hydrazine (8) with loss of nitrogen.

Notes: 1-Aryl- and 1-Alkyl-2-phathalimido-diazene-1-oxides, Diacylated Examples of Trisubstituted Triazene-1-oxides: Formation, Properties, Stereoisomerization and Fragmentation1)Oxidatively generated phthalimido-nitrene (1) reacts with nitrosobenzene (8a), p-nitrosotoluene (8b), o-nitrosotoluene (8c), p-dimethylamino-nitrosobenzene (8d), p-methoxycarbonyl-nitrosobenzene (8e), 1, 1-dimethyl-1-nitrosoethane (8f) and nitrosocyclohexane (8g) to give the respective 1-substituted (Z)-2-phthalimidodiazene-1-oxides 14a-g.The constitution of 2-imidodiazene-1-oxides 14 is deduced from their spectroscopic properties. The UV. spectra of 14a-e are similar with those of the corresponding nitrobenzenes 18, thus supporting the concept of comparibility of the phthalimido-N group with an O-atom and indicating that the phthalimido group is not in conjugation with the diazene-oxide function.This is in contrast to the situation in the non-acylated trisubstituted triazene-1-oxides 12, where conjugation is extended over the chain of all three N-atoms as exhibited by the UV. spectra of (Z)-1, 3, 3-triphenyl-, (Z)-3, 3-dimethyl-1-phenyl-, (Z-3-methyl-1, 3-diphenyl-, (Z)-1-(1, 1-dimethylethyl)-3, 3-diphenyl-, and (Z)-1-(1, 1-dimethylethyl)-3, 3-dimethyltriazene-1-oxide (12a-e). These triazene-1-oxides are formed by the reaction of 1, 1-disubstituted hydrazines 11 with three mol-equiv. of nitroso compounds 8 or from equimolar amounts of 11 and 8 in the presence of mercury oxide. Over 90% of 1, 2-diphenyldiazeneoxide (19, R = C6H5) are isolated by the reaction 11 + 3 8a. Possible mechanisms of the reaction of 11 with 8, and of the formation of 12 via triazanols D and of 19 (R = C6H5) via N-Phenylhydroxylamine (20, R = C6H5) are given in Scheme 6 (in the latter case with experimental evidence). An independent synthesis of 12c confirms the constitutional assignment for 12.

Notes: 3,3-Dialkyltriazenecarboxylic Derivatives by Oxidative Hydro-Acyl-Elimination from 3,3-Dialkyltriazane-1,2-dicarboxylic DerivativesThe preparation and some properties of esters and amides of 3,3-dialkyltriazenecarboxylic acids (6) are described. These novel triazenes 6 were obtained by treatment of diesters, diamides and ester-amides of 3,3-dialkyltriazane-1,2-dicarboxylic acids (3) with lead tetraacetate, when an elimination of the COOR- or the CONHR-group at N(2) together with the H-atom at N(1) took place. The precursor triazanes 3 were readily available from the addition of secondary amines 2 to diesters, diamides or ester-amides of diazenedicarboxylic acid (1). The spectral properties of the triazanes 6, including the 15N-NMR signals of one example, are compared with those of the triazanes 3. They express the structural features due to conjugation in 3,3-dialkyltriazenecarboxylic derivatives, including the resistance to rotation around the N(2), N(3)-bond.

Notes: 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.

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.