Allene cycloadditions. Part III. Synthesis of alkylidenecyclobutenes

Abstract

Thermal cycloaddition of chlorotrifluoroethylene and 1,1-dichlorodifluoroethylene to allene gives mixtures of two 1 : 1 adducts, identified as the 1-halogeno-1-chloro-2,2-difluoro-3-methylenecyclobutanes (Ia and b) and the 2-halogeno-2-chloro-1,1-difluoro-3-methylenecyclobutanes (IVa and b)(halogeno = Cl or F). Base-catalysed elimination of hydrogen fluoride from 1 -halogeno-1,2,2-trifluoro-3-alkylidenecyclobutanes (Ic–e) and of hydrogen chloride from the related 1-chlorides (Ib, e, and f) affords 1-halogeno-4,4-difluoro-3-alkylidenecyclobutenes (IIIa–c). The n.m.r. and mass spectra of these and related compounds are discussed.