Stereoselective synthesis of enantiomerically pure beta-fluoroalkyl gamma-butyrolactones by sulfoxide-directed lactonization

Enantiomerically pure alpha,alpha-dichloro beta-fluoroalkyl gamma-p-tolylth io gamma-butyrolactones trans-6a-c have been obtained with excellent stereo control (> 98:2) and enantiomeric purity (> 98:2) by sulfoxide-directed lac tonization (Marino's annulation reaction) of beta-fluoroalkyl vinyl sulfoxi des (R)-(E)-5a-c with dichloroketene. Highly chemoselective dechlorination and desulfurization reactions performed on trans-6c efficiently provided th e beta-chlorodifluoromethyl gamma-butyrolactone (S)-8c, the absolute stereo chemistry of which was determined by X-ray diffraction analysis of its gamm a-p-tolylthio precursor (2R,3S)-7c.