Allene cycloadditions. Part II. Reaction of a dialkylallene with unsymmetrical fluoro-olefins: evidence for a two-step [2 + 2] cycloaddition

Abstract

Thermal cycloaddition of chlorotrifluoroethylene and 1,1-dichlorodifluoroethylene to 3-methylbuta-1,2-diene gives mixtures of four 1 : 1 adducts, identified as the 3-halogeno-3-chloro-2,2-difluoro-1-isopropylidenecyclobutanes (Ib, c), the 3-halogeno-3-chloro-2,2-difluoro-4,4-dimethyl-1-methylenecyclobutanes (IIb, c), the 2-halogeno-2-chloro-3,3-difluoro-1-methyl-1-vinylcyclobutanes (IIIb, c), and the 2-halogeno-2-chloro-3,3-difluoro-1-isopropenylcyclobutanes (IVb, c)(where halogeno = Cl or F). The effect of temperature on the product distribution in the reactions of 3-methylbuta-1,2-diene with tetrafluoroethylene and with chlorotrifluoroethylene has been studied. The results are discussed in relation to a stepwise cycloaddition mechanism via an intermediate diradical.