The (2+ 2) cycloadditions of 1, 3-di-t-butylallene-1, 3-dicarbonitrile (3) to azomethines or an acyclic amidine afford 2-alkylidene azetidines 12, 19. In the reaction of 3 with the 3- dimethylamino-2H-azirine 20 the 1, 2 bond of the 3-membered ring is cleaved to give the stereoisomeric 1-pyrrolines 23.