Development of New Functions of Organochalcogenic Compounds and Its Development

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This investigation is mainly based on the concept "Stabilization of chiral chalcogenic compounds by the stericbulkiness and the hydrogen bonding", which provides a novel method for the preparation of chiral chalcogenic compounds such as chiral selenoxides, selenuranes, and telluranes by using 2-exo-hydroxy-10-bornyl group as a chiral ligand.A) Asymmetric synthesis of chiral selenium compoundsThe first synthesis of optically pure haloselenuranes has been accomplished by utilizing the 2-exo-hydroxy-10-bornyl group as a chiral ligand. Complete retention of the configuration has been observed in inter-conversion reactions between haloselenuranes and selenoxides and in nucleophilic substitution reaction of those haloselenuranes. For example, nucleophilic substitution reaction of the chloroselenurane with active methylene compounds proceeded in highly stereoselective manner with retention of configuration to give the corresponding selenonium ylides.B) Asymmetric synthesis of chiral tellurium compoundsThe first synthesis and isolation of optically pure Te-chiral-alkoxytelluranes have been developed using the 2-exo-hydroxy-10-bornyl group as a chiral ligand. A distorted trigonal bipyramidal structure was confirmed by the X-ray analysis.C) Asymmetric reaction utilizing chiral selenoxidesi) Asymmetric protonation of enolatesEnantioselective protonation of a simple enolate has been developed using an optically pure gamma -hydroxy- selenoxide having the 2-exo-hydroxy-10-bornyl group as a chiral ligand as a chiral proton source.ii) Asymmetric [2,3] sigmatropic rearrangement of allylic selenium compoundsThe [2,3] sigmatropic rearrangement of allylic selenimides proceeds predominantly via the endo transition state, and is available for practical preparation of various chiral allylic amines. The methodology is applicable to the preparation of of various chiral allylic selenoxides and homoallylic compounds.