Orthoamide und Iminiumsalze, XCVIa. Push-pull-substituierte 1,3,5-Hexatriene aus Orthoamiden von Alkincarbonsäuren und Birckenbach-analogen Acetophenonen

From acetone and the orthoamide of phenylpropiolic acid (21b) N,N-dimethyl-phenylpropiolic acid amide (24) is formed. In contrast, the reaction of chloroacetone (28) with 21b results in the vinylogous guanidinium chloride 29. Unexpectedly, the Birckenbach-analogoue ethyl methyl ketone (34) reacts with the orthoamide 21b to give the push-pull-substituted butadiene 36. In contrast to this observation, the reaction of the Birckenbach-analogous acetophenones 30 with the orthoamides 21a–c delivers the push-pull-substituted 1,3,5-hexatrienes 31a–j.