OPTICALLY PURE CHALCOGENURANES: SYNTHESIS AND STEREOCHEMISTRY OF THEIR REACTIONS

Abstract

An overview of our recent studies on the asymmetric syntheses, stereochemical studies, reactions and applications of chiral chalcogenuranes is described. Chiral chalcogenuranes, including halooxachalcogenuranes and spirooxachalcogenuranes, have been synthesized by highly diastereoselective oxidation of the 2-exo-hydroxy- 10-bornyl chalcogenides. The stereochemistry of chalcogenuranes have been confirmed as with a trigonal bipyramidal (TBP) geometry. Nucleophilic substitution reactions of these compounds provided a good method to prepare the chiral chalcogenonium (IV) compounds with excellent diastereoselectivity. Our results indicated that the reactivity of the axial bonds of chalcogenuranes plays an important role in the control of the stereochemistry of the reactions. The mechanistic and stereochemical research on the nucleophilic substitution reactions have been carried out which indicated that two kinds of pathways, dissociative and associative routes, might exist. The applications of the reactions through the asymmetric [2, 3] sigmatropic rearrangement and enantioselective protonation with optically active selenonium (IV) compounds have been investigated to give good to high selectivities.