Labelled organophosphorus pesticides IV. Syntheses of optically active O‐aryl O‐ethyl phenylphosphonothioates labelled with carbon‐14

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Optically active O‐p‐cyanophenyl O‐ethyl phenylphosphonothioate (cyanofenphos) (1) and O‐ethyl O‐p‐nitrophenyl phenylphosphonothioate (EPN) (2), organophosphorus insecticides, were labelled with carbon‐14 at the phenyl ring of the phenylphosphonothioic acid moiety for use in metabolic studies. The synthetic procedures were shown in Fig. 1. Treatment of benzene‐14C6 with phosphorus trichloride in the presence of anhydrous aluminum chloride followed by sulfurization with sulfur gave phenyl‐14C6‐phosphonodichloridothioate (3). Reaction of 3 with ethanol gave O‐ethyl phenyl‐14C6‐phosphonochloridothioate (4). Hydrolysis of 4 gave (±)‐O‐ethyl phenyl‐14C6‐phosphonothioic acid (5). Optical resolution of 5 with brucine afforded (−)‐ and (+)‐enantiomers (5a and 5b), which were chlorinated with oxalyl chloride to give (−)‐ and (+)‐chloridothioates (4a and 4b), respectively. Condensation of 4a and 4b with p‐cyanophenol yielded (+)‐ and (−)‐cyanofenphos‐(phenyl‐14C6) (la and lb) in the overall yields of 4.0 and 4.5%, respectively. Similarly, condensation of 4a and 4b with p‐nitrophenol afforded (+)‐ and (‐)‐EPN‐(phenyl‐114C6)(2a and 2b) in the overall yields of 4.2 and 5.5%, respectively.