AB-INITIO INVESTIGATION ON NUCLEOPHILIC RING-OPENING OF 1,3,2-OXATHIAPHOSPHOLANE - NUCLEOPHILIC-SUBSTITUTION AT PHOSPHORUS COUPLED WITH PSEUDOROTATION

Ab initio investigations on the reaction profiles for the base-catalyz ed methanolysis of amino-2-thiono-1,3,2-oxathiaphospholane suggested t hat the ring opening with retention of configuration at phosphorus wou ld be energetically most favorable. This provides the rational interpr etation for the chemo- and stereoselectivity ascertained experimentall y for the reaction. The pseudorotation process is strongly coupled wit h the reaction coordinate for the substitution pathway, which suggests that substitution with retention of configuration can occur in genera l even though the trigonal bipyramidal species resulting from pseudoro tation is significantly unstable and fails to exist as an intermediate .