Acid-catalysed methanolysis of (N-aryl)methylphenylphosphinic amides: changes in the stereochemistry resulting from nucleophilic participation by chloride ion

Abstract

(S):(N-Phenyl)methylphenylphosphinic amide (1) and its (N-p-nitrophenyl)(2) and (N-p-methoxyphenyl)(3) analogues react stereospecifically in methanolic trifluoromethanesulphonic acid to give methyl methylphenylphosphinate (4) with complete inversion of configuration. The presence of lithium trifluoromethanesulphonate does not disturb the stereochemistry, but the presence of lithium chloride causes some of the phosphinate(4) to be formed with retention of configuration. Chloride ion apparently acts as a nucleophilic catalyst and thereby provides an alternative (retention) to the direct (inversion) methanolysis pathway. The proportion of reaction proceeding with retention depends on the nucleophilicity of the leaving group in the amide, decreasing in the order (3)(1) > (2).