Lewis Acid/Base Catalyzed [2+2]-Cycloaddition of Sulfenes and Aldehydes: AVersatile Entry to Chiral Sulfonyl and Sulfinyl Derivatives

The first catalytic asymmetric synthesis of beta-sultones is reported. This development has enabled a rapid access to a number of highly enantioenriched biologically interesting sulfonyl and sulfinyl compound classes, which makes use of the inherent ring strain of the four-membered heterocycles. The products possess either two vicinal stereocenters, such as in beta-hydroxy-sulfonamides, -sulfonates, -sulfones, -sulfonic acids, -sulfinic acids, gamma-sultines, and gamma-sultones or a single stereocenter, such as in alpha-branched alkyl or allyl sulfonic acids. This work also represents the first application of sulfene intermediates in asymmetric catalysis. The reactivity of a sulfene normally acting as an electrophile could be reverted by the formation of a nucleophilic zwitterionic sulfene-amine adduct. To achieve a combination of high enantioselectivity and reactivity, cooperative catalytic action of a chiral nucleophilic tertiary amine (the cinchona alkaloid derivative diydroquinine 2,5-diphenyl-4,6-pyrimidinediyl diether ((DHQ)(2)PYR)) and Bi(OTf)(3) or In(OTf)(3) was of primary importance.