SYNTHESIS OF ALLENES VIA THERMAL CYCLOREVERSION OF ALPHA-ALKYLIDENE-BETA-LACTONES

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