Synthesis and Chemical Reactivity of Methoxycarbonyl-1,3-dioxinyl(pivaloyl)ketene — A Persistent α-Oxoketene.

Flash vacuum pyrolysis of an equimolar mixture of 4-pivaloyl- and 4-methoxycarbonyl-5-tert-butylfuran-2,3-dione affords the new and remarkably stable α-oxoketene 6 as the result of an unusual dimerization of the primarily formed monomeric α-oxoketenes 1 and 3, respectively. [2 + 2] Cycloaddition reactions of 6 and dialkylcarbodiimides furnish functionalized imino-β-lactams 7, while reaction with nucleophiles results in complete degradation of 6 into smaller fragments. Structural confirmation of 6 and 7 is mainly based upon single crystal X-ray analyses.