Optically Pure Chalcogenuranes. Synthesis and Stereochemical Research of Their Reactions.

An overview of the recent studies on the asymmetric syntheses, stereochemical studies, reactions and applications of chiral chalcogenuranes is described. Chiral chalcogenuranes, including halooxachalcogenuranes and spirochalcogenuranes, have been synthesized by highly diastereoselective oxidation of the 2-exo-hydroxy-10-bornyl chalcogenides. The stereochemistry of chalcogenuranes have been confirmed to be trigonal bipyramid (TBP): Nucleophilic reactions of these compounds provided a good method to prepare the chiral chalcogenonium (N) compounds with excellent diastereoselectivity. Hydrolysis of the chiral spirosulfurane gave optically pure sulfoxides with different stereochemistry at the sulfur atom under various conditions, which indicated that the reactivity of the axial bonds plays an important role in the control of the stereochemistry of the reactions. Mechanistic and stereochemical studies on the nucleophilic reactions have revealed that two kinds of pathways, dissociative and associative routes, seem to exist. The application of the reactions through the [2,3] sigmatropic rearrangment and enantioselective protonation with optically active selenonium compounds have been investigated to give good selectivities of the reactions.