Addition of Cl_2C: to (-)-O-Menthyl Acrylate under Sonication-Phase-Transfer Catalysis. Efficient Synthesis of (+)- and (-)-(2-Chlorocyclopropyl)methanol

摘要

Dichlorocyclopropanation of (—)-O-menthyl acrylate under conditions of phase-transfer catalysis (CHCl_3, KOH, tetram-ethylammonium bromide), with sonication, gives excellent yields (85-94%) of the corresponding dichlorocyclopropan-ecarboxylate ester compared to thermal conditions (90 ℃, 56%). No diastereoselectivity was observed, but one isomer was isolated pure by fractional crystallization. The measured kinetic isotope effect (initial rate (CHCl_3)/rate (CDCl_3) ～1.7) suggests deprotonation of CHCl_3 as the rate-limiting step.