Cycloadditions of 1‐Thia‐3‐azoniabutatriene Salts to Azomethines, Carbodiimides, and Ketene Imines

A new method for the preparation of sulfur‐substituted 2‐azoniaallene salts ( 3a – f, 5a – d, 7 ) by [2 + 2] cycloadditions of 1‐thia‐3‐azoniabutatriene salts ( 1c,d ) to azomethines ( 2a – f ), carbodiimides ( 4a – d ), and the ketene imine 6 is described. The X‐ray crystal analysis of the adduct 3b of 4‐(dimethylamino)‐4‐phenyl‐1‐thia‐3‐azoniabutatriene hexachloroantimonate ( 1d ) to N ‐benzylidene‐ p ‐toluidine ( 2b ) shows an almost planar 2‐azaallylium cation with a W‐shaped arrangement of the N–C–N–C–N fragment, the plane of which also contains the 1,3‐thiazetidine ring. Improved methods for the preparation of 1d and the corresponding tetrachloroaluminate ( 1e ) are given.