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-catalyzed methanolysis of amino-2-thiono-1,3,2-oxathiophospholane suggested that the ring opening with retention of configuration at phosphorus would be energetically most favorable. This provides the rational interpretation for the chemo- and stereoselectivity ascertained experimentally for the reaction. The pseudorotation process is strongly coupled with the reaction coordinate for the substitution pathway, which suggests that substitution with retention of configuration can occur in general even though the trigonal bipyramidal species resulting from pseudorotation is significantly unstable and fails to exist as an intermediate.