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

Rigid 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 = CH 2 ) 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 ).