Synthesis of allenes via thermal cycloreversion of .alpha.-alkylidene-.beta.-lactones

This paper describes the application of the solution-phase [2+2] cycloreversion of α-alkylidene-β-lactones as a practical method for the generation of substituted allenes. Upon heating in dimethylformamide solution at 110-125 o C, these unsaturated β-lactone derivatives undergo decarboxylation to provide allenes in good to excellent yield. α-Alkylidene-β-lactones are conveniently prepared via the phenylselenylation of β-lactone enolates followed by oxidative elimination of the resulting α-phenylseleno derivatives. The β-lactone starting materials are synthesized by the addition of thiol ester enolates to ketones and aldehydes according to our recently reported procedure