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

Abstract

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.