ASYMMETRIC-SYNTHESIS VIA OPTICALLY-ACTIVE VINYL SULFOXIDES

The reaction of chiral vinyl sulfoxides with dichloroketene to yield optically active gamma-butyrolactones provides the basis for enantioselective syntheses of heterocyclic natural products. In particular, 2-alkylsulfinylindoles are transformed into butyrolactones that serve as precursors to the physostigmine alkaloids. The total synthesis of physostigmine in optically active form has revealed the importance of the size of alkyl group of the sulfoxide in the 3,3-sigmatropic rearrangement leading to the chiral butyrolactone. In addition, an efficient synthesis of optically active benzohydrofuran lactones which are precursors to the aflatoxins is described.