Synthesis of New 1,3-Oxaphosphorinanium Salts. Stereochemistry of Hydroxide-Induced Displacement of Methoxide Ion

The synthesis of pure cis- and trans-3-methoxy-2,2,6-trimethyl-3-phenyl-1,3-oxaphosphorinanium
tetrafluoroborate salts 3a and 3b, respectively, molecules designed to evaluate the effect of oxygen
on the steric course of base-induced nucleophilic displacement of the methoxy group at phosphorus,
was accomplished. It was found that these isomeric salts react with aqueous sodium hydroxide to
produce the corresponding phosphine oxides 7a and 7b with complete retention of configuration at
phosphorus.