Unprecedented formation of stable ketene-N,O-acetals and their rearrangement under basic conditions

Treatment of 2,4-disubstituted glutaryl dichlorides with benzimidic acid ethyl ester hydrochloride in the presence of triethylamine did not give the expected bis(acylbenzimidates), but delivered O-acyl-N-ethoxybenzylidene-ketene-N,O-acetals in good to excellent yields. These compounds, which are stable to moisture and chromatography on silica gel, underwent an unprecedented rearrangement to cyclic enamides under stronger basic conditions. A mechanism for this rearrangement is proposed.