Synthesis of Highly Pure Enantiomers of the Insecticide Salithion

Abstract

Optically active salithion (>98% e.e.) was obtained via an L-proline methyl ester derivative (PS), whose diastereomers were easily separated, with subsequent sulfuric acid-catalyzed methanolysis. The configuration of each diastereomeric PS was determined by NMR and single-crystal X-ray analysis. *The optical purity of each PS and of the salithion enantiomers was measured by ¹H-NMR and HPLC, respectively. The sulfuric acid-catalyzed methanolysis of PS to salithion was confirmed to have proceeded with an inversion of the configuration at the phosphorus atom by an experiment using model compounds.