Evidence for Ketene Intermediates in the Reactions of 2-Oxobutanedioic Acid Diesters with Alcohols and Water

Article abstract of DOI:10.1021/jo00298a037

The reactions of diethyl ester (1a) and dimethyl ester (1b) of 3-methyl-2-oxobutanedioic acid with excess ethanol, methanol, or water in a sealed tube at approximately 125 deg C were studied.With methanol, 1a yielded mainly 3-methyl-2-oxobutanedioic acid 1-ethyl 4-methyl diester, 2a; with ethanol, 1b yielded mainly the 4-ethyl 1-methyl diester, 2b, while reaction of 1a with water yielded carbon dioxide, 2-oxobutanoic acid ethyl ester, 6, and 2-methyl-3-oxopropanoic acid ethyl ester, 7.These results suggested that the ketene intermediates 3-methyl-2,4-dioxo-3-butenoic acid ethyl or methyl ester, 4a and 4b, respectively, are implicated.The similarity of these reactions to those exhibited by ethyl acetoacetate, such as alkoxy group exchange, and formation of dehydroacetic acid, now thought to proceed by way of acetyl ketene, was demonstrated.