Abstract The [2+ 2]-cycloaddition of dichloroketene (prepared in situ from CCl 3 COCl and Zn (Cu)) with three alkynes 1a–c to form 2, 3-dimethyl-(2a), 2, 3-diethyl-(2b) and 3-butyl-4, 4- dichlorocyclobut-2-enone (2c) proceeds rapidly in the absence of POCl 3. The primary products 2a–c rearrange in situ to the 2, 4-dichlorocyclobut-2-enones 3a–c under the influence of ZnCL 2 produced during the reaction. ZnCl 2 converts both 2a and 3a into a 4: ...
