Improved Synthesis of 2-Chlorocyclobutanone Derivatives

摘要

2-Halocyclobutanones are valuable intermediates for the synthesis of cyclopropanecarboxylic acid derivatives, which are useful components for biologically active compounds such as pesticides. Various syntheses of 2-halocyclobutanones have been reported, but most of them were complicated and few were achievable in a single step. For example, reductive dehalogenation of 2,2-dichlorocyclobutanones, prepared by the reaction of dichloroketene and oiefins, was necessary to give 2-chlo-rocyclobutanones. Thereaction of alkylchloroketene and terminal oiefins gave 2-alkyl-2-chlorocyclobutanones, which were subsequently rearranged into 2-alkyl-4-chlorocyclobutanones. The only report of a one-step synthetic procedure was the reaction of α,α-dichloroacetyl chloride and oiefins. In this reaction, the generation of chloroketene fom α,α-dichloroacetyl chloride by the reaction with zinc dust was proposed. α-Chloroacetyl chloride has been considered quite useless for the generation of chloroketene, although itis one of the most readily available reagents. Chloroketene has been estimated to be very unstable in contrast with rather stable dichloroketene, and its synthetic applications for [2 + 2] cycloaddition with ketenophiles, such as oiefins, have been thought to be rather limited.