Studies related to thiirans. Part 1. Synthesis of chiral thiirancarboxylates

Abstract

The first examples of optically active thiirancarboxylic acid derivatives are reported. Thus optically pure methyl (S)-thiirancarboxylate was prepared by the reaction of methyl (R)-cysteinate with sodium nitrite–hydrochloric acid; ethyl and n-propyl (S)-thiirancarboxylates were obtained in an analogous manner. (R)-Cysteine undergoes a corresponding deaminative cyclization to give (R)-thiirancarboxylic acid; the optical purity of the last-mentioned compound is 53% when dilute hydrochloric acid is employed as the reaction medium and 60% when aqueous acetic acid is used. Methyl (S)-thiirancarboxylate is hydrolysed by sodium hydroxide to (S)-thiirancarboxylic acid; the reaction occurs without any significant racemization. (S)-Penicillamine methyl ester reacts with sodium nitrite–hydrochloric acid to give optically pure methyl(R)-3,3-dimethylthiiran-2-carboxylate. (S)-Penicillamineufilndergoes an analogous reaction to give (S)-3,3-dimethylthiiran-2-carboxylic acid with an optical purity of 87%.