Thermolysis of polyazapentadienes. Part 11. Concerted and free radical mechanisms in 2-aza enone and 2-aza enthione pyrolyses: crystal and molecular structures of 3-dimethylamino-1-p-tolyl-2-azaprop-2-en-1-one and 3-dimethylamino-1-phenyl-2-azaprop-2-ene-1-thione

Abstract

Flash vacuum pyrolysis of the dimethylamino-azapropenones (7)–(9) and -azapropenethione (12) gives nitrites and amides (or thioamide) in yields of ca. 30% by an electrocyclisation-ring cleavage mechanism. This is a minor pathway for the triarylazapropenones (14) and (15) for which homolytic cleavage of the C–N bond gives rise to the major products. The X-ray crystal structures of (10) and (12) show that the conjugated systems are almost planar in the s-Z conformation, as required for the electrocyclic ring closure.