The mechanism by which a, y-dioxo carboxylic acid esters 1 and 2-oxobutanedioic acid diesters 2 lose CO W~ S explored. The compounds, 5, 5-dimethyl-2, 4-dioxohexanoic acid ethyl ester, la, a, 2-dioxocyclohexaneacetic acid ethyl ester, lb, and a, l-dioxotetrahydro-2- naphthaleneacetic acid ethyl ester, IC, lose CO at 170-190" C to yield the corresponding &keto esters 3a-c. When compounds 1 or the parent acids 4 were heated to 170-190" C ...