Triaziridine. II. Erste Beispiele: 2, 3-Dialkyl-triaziridin-1-carbonsäurealkylester

Triaziridines. II. First Examples: Alkyl 2,3-Dialkyl-triaziridine-1-carboxylates The 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.