Asymmetric Synthesis of Chiral Sulfinate Esters and Sulfoxides. Synthesis of Sulforaphane

Reaction of the chiral auxiliary trans-2-phenylcyclohexanol (1) with thionyl chloride afforded a nearly equal mixture of two diastereomeric chlorosulfite esters (6). Treatment of this mixture with an equivalent amount of a dialkylzinc reagent (Me, Et, i-Pr) afforded high levels of conversion of both chlorosulfite esters to (mainly) a single diastereomer of the sulfinate ester (7). Levels of absolute stereochemical induction ranged from 10:1 to 96:4 under conditions affording high chemical yields. The method was employed for the separate synthesis of both enantiomers of sulforaphane (13).