Addition of Cl₂C:  to (−)-O-Menthyl Acrylate under Sonication−Phase-Transfer Catalysis. Efficient Synthesis of (+)- and (−)-(2-Chlorocyclopropyl)methanol

[reaction: see text] Dichlorocyclopropanation of (-)-O-menthyl acrylate under conditions of phase-transfer catalysis (CHCl3, KOH, tetramethylammonium bromide), with sonication, gives excellent yields (85-94%) of the corresponding dichlorocyclopropanecarboxylate ester compared to thermal conditions (90 degrees C, 56%). No diastereoselectivity was observed, but one isomer was isolated pure by fractional crystallization. The measured kinetic isotope effect (initial rate (CHCl3)/rate (CDCl3) approximately 1.7) suggests deprotonation of CHCl3 as the rate-limiting step.