Azo Bridges from Azines, XVIII. Transformation of CC Bonds into Cyclopropanes, Aziridines and Oxiranes in the Presence of Azo Groups

Abstract

AbstractRigid systems of type B in which a three‐membered ring and an azo group are located in a rigid close and parallel position were synthesized by variation of both the hetero group X and the carbocyclic framework. Both the cyclopropane (X = CH2) and the aziridine (X = N‐R) moieties are introduced by [3 + 2] cycloaddition reactions of diazomethane (1, 15, 18, 20) or azides (26/1–5, 35, 38, 41, 44) to CC‐double bonds and subsequent denitrogenation of the cycloadducts. By thermal and photochemical (300 nm) denitrogenation the triazolines were smoothly transformed into the expected aziridines (27/1–5) whereas catalysis by silica gel party caused additional rearrangements (28, 37, 40, 43, 46). Chemoselective photo‐denitrogenation of azo/pyrazolines 16 and 19 was not possible, but could be achieved by starting from azoxide/pyrazolines 21 with subsequent reduction of the azoxy group (23→9, 24 → 25). Similarly, azo/oxiranes 48 and 55 were prepared by oxygenation of unsaturated azoxides (e.g. 20) and chemoselective deoxygenation of the azo group by irradiation in methanol (49→48, 54→ 55).