The stereochemistry of methanolysis reaction of trans-2-chloro- 4- phenyl-5, 5-dimethyl-1, 3, 2-dioxaphosphorinane 2-oxide (trans-1) and cis-2-chloro-4-phenyl-5, 5-dimethyl-1, 3, 2-dioxaphosphorinane 2- sulfide (cis-2) were described. Trans-1 was treated with methanol to give inversion product at phosphorus. In contrast, retention is favored while the reaction employs methoxide ion as the nucleophile. Reaction of cis-2 with sodium methoxide in methanol under reflux led to a ring opening followed by ring closure to give a thermodynamically controlled mixture of diastereomeric isomers in which trans isomer was the major component. An acyclic intermediate is found to be involved in this process.

Key words: DIOXAPHOSPHORINANE P, ISOMERIZATION REACTION, RING CLEAVAGE REACTION, STEREOCHEMISTRY