Interrelationship between carboxy(vinyl)ketenes, methyleneketenes, vinylketenes, and hydroxyacetylenes

Carboxy(vinyl)ketenes, alkylideneketenes, and vinylketenes have been obtained selectively, sequentially, and isomerically pure for the first time by flash vacuum pyrolysis of 2,2-dimethyl-5-alkylidene-1,3-dioxane-4,6-diones (Meldrum's acid derivatives) under controlled conditions. Each of the ketenes was directly observed by IR spectroscopy and trapped with methanol or aniline. Highly unstable compounds believed to be the hydroxyacetylene isomers of the alkylidene- and vinylketenes have been observed for the first time