Stereochemical Studies of Chiral Nonconjugated Carbanions. Asymmetric Alkylation of Aldehydes with Sulfur-Substituted Carbanions of Chiral .ALPHA.-1,3-Dithian-2-yl) Acetals.

A new type of asymmetric induction based on the nucleophilic addition of sulfur-substituted nonconjugated carbanions produced from a variety of chiral alpha-(1,3-dithian-2-yl) acetals to achiral aldehydes was studied. The reaction with the carbanion of the chiral acetal derived from (4R,5R)-3,6-diethyl-3,6-dimethoxy-4,5-octanediol showed the best stereoselectivity (ds=2.4:1-6.3:1) producing a chiral secondary-alcohol center.