Carboxy(vinyl)ketene intermediates in the thermolysis of methylthio- and methoxy-substituted Meldrum’s acid derivatives

Abstract

Methylthio- and methoxy-substituted carboxy(vinyl)ketenes 10 and 16a have been identified by Ar matrix isolation FTIR spectroscopy following flash vacuum thermolysis (FVT) of Meldrum’s acid derivatives 7 and 13a. Methylthio(methyl)methyleneketene 9 and alkoxy(methyl)methyleneketene 15 are formed concurrently at high FVT temperatures. The alkoxy(methyl)methyleneketenes 15 do not isomerise to alkoxy(vinyl)ketenes 18, which have been generated and identified in other reactions. Ethoxy(methyl)methyleneketene 15b readily eliminates ethene in a retro-ene type reaction to produce acetylketene 22. Ketenes 15 react with alcohols and amines to produce 3-alkoxybutenoic acid derivatives 21.