AN EFFICIENT METHOD FOR GENERATION OF ALPHA-OXOKETENES - CYCLOREVERSION OF ENOLIZED MELDRUMS ACID-DERIVATIVES

A series of 6-methoxy- or siloxy-4H-1,3-dioxin-4-ones was synthesized from Meldrum's acids. These dioxinones underwent 4+2 cycloreversion to methoxy-or siloxycarbonylketenes and ketones quantitatively at 20-50 degrees C. The ketenes were characterized by IR spectroscopy as well a s by trapping with t-butanol. The ready cycloreversion of these enoliz ed Meldrum's acid derivatives strongly indicates that the anomalously high susceptibility of Meldrum's acids to nucleophilic reagents is due to the participation of carboxyketenes generated through the cyclorev ersion of tautomeric 6-hydroxydioxinones. (C) 1997 Elsevier Science Lt d.