An Improved Procedure for the Addition of Dichloroketene to Unreactive Olefins

The cycloaddition of dichloroketene to hindered or unreactive olefins has, in the past, enjoyed only limited success. Not only are a large excess of the olefin or acid halide necessary, but the yields are often low. Most of these problems have now been overcome by dehalogenating trichloroacetyl chloride with activated zinc in the presence of the olefin and phosphorus oxychloride. Under these conditions, dichloroketene can even be added to tri- and tet-rasubstituted olefins. An important feature of this procedure is that often only a small (5%) excess of acid chloride is necessary. The phosphorus oxychloride may function by complexing the zinc chloride produced in the reaction. Although styrene, which is normally polymerized by zinc salts, is transformed in good yield to the cyclobutanone adduct by this method, the very sensitive olefins dihydropyran and cyclopentadiene fail to yield isolable dichloro-cyclobutanones.