Stereochemistry of base-induced cleavage of methoxide ion on cis- and trans-1,4-diphenylphosphorinanium salts. A different behavior with a phenyl substituent

The synthesis and characterization of pure cis- and trans-1,4-diphenyl-1-methoxy-phosphorinanium tetrafluoroborate salts 11a and 11b, molecules designed to evaluate the effect of a phenyl substituent at C-4 on the stereochemical course of base-induced nucleophilic displacement of the methoxy group at phosphorus, was accomplished. The presence of a phenyl substituent at C-4 changes the stereochemical course of these reactions, from complete inversion with alkyl groups to products where retention of configuration at phosphorus predominates. We suggest a mechanism involving Berry pseudorotations and provide evidence that the hydroxide ion attacks the phosphorus atom through experiments with NaOH enriched with ¹⁷O.