Orthoamide und Iminiumsalze, CIV. Umsetzungen von Orthoamiden der Alkincarbonsäuren mit enolisierbaren Carbonylverbindungen – Cyclisierung der Kondensationsprodukte zu Pyran-Derivaten

Orthoamides of alkynecarboxylic acid 15 condense with enolisable β-dicarbonyl compounds and as well with acetophenones to give 3-acryl-1,1-bis(dimethyl-amino)-1,3-butadienes. Some acylbutadienes cyclize affording 2-pyranon-derivatives 33 upon heating with aqueous ethanol. 2H-pyranes are accessible from acetone dicarboxylic acid ester and orthoamides 15. The constitution of one 4-acyl-1,1-bis(dimethylamino)-1,3-butadiene (16f) and one 2H-pyrane (44b) was confirmed by crystal structure determinations.