synthetic route to 5- and 6-membered 3-cyano-2-oxo-1,2-thiaphosphacyclanes and 6-cyano-2-oxa-10-oxa(thia)-phosphabicyclo [4.4.0]-decane-1-oxides was elaborated via intramolecular S-alkylation in a series of y -haloalkylsubstitutedthiophosphorylacetonitriles. The compounds were used to prepare novel P(III)-containing bidentate ligands with definite stereochemistry. Diastereomeric transformations among