Reactions of nucleophilic carbenes with enols

The formal insertion of dimethoxycarbene (la) into the acidic C-H bond of pentane-2,4-dione (9a), methyl acetoacetate (9b), 3-methylpentane-2,4-dione (9c) and 1,3-diphenylpropane-1,3-dione (9d) is reported as well as the insertion of 3-benzoyloxazolidin-2-ylidene (Ib) into 9c, The beta-dicarbonyl compounds 9 are known to be equilibrated with their corresponding enols in benzene solution and the insertions appear to proceed by proton abstraction from the enol tautomers of 9 to generate enolate anions and either a dimethoxymethyl cation (from la)ora 3-benzoyloxazolidin-2-ium cation (from Ib), Collapse of these ion pairs at the carbon atom of the enolate yields the major product, Formal insertion of la into the O-H bond of the enol tautomer of anthrone (12) is also reported.