Stereoselective Synthesis of Enantiomerically Pure β-Fluoroalkyl γ-Butyrolactones by Sulfoxide-Directed Lactonization

Enantiomerically pure α,α-dichloro β-fluoroalkyl γ-p-tolylthio γ-butyrolactones trans-6a–c have been obtained with excellent stereocontrol (> 98:2) and enantiomeric purity (> 98:2) by sulfoxide-directed lactonization (Marino's annu-lation reaction) of β-fluoroalkyl vinyl sulfoxides (R)-(E)-5a–c with dichloroketene. Highly chemoselective dechlorination and desulfurization reactions performed on trans-6c efficiently provided the β-chlorodifluoromethyl γ-butyrolactone (S)-8c, the absolute stereochemistry of which was determined by X-ray diffraction analysis of its γ-p-tolylthio precursor (2R,3S)-7c.