Selective Formation of Five-Membered Heterocyclic Products by Anodic Oxidation of Alkyl Isothiocyanates (RNCS)in Dichloromethane and Their Thermal Isomerization and Decomposition

Anodic oxidation of primary and secondary alkyl isothiocyanates (RNCS) in dichloromethane yielded two isomers of five-membered heterocyclic products, 4-alkyl-5-(alkylimino)-1,2,4-dithiazolidine-3-one 2 and 2,4-dialkyl-5-oxo-l,2,4-thiadiazolidine-3-thione 3. Their relative ratio was found to be dependent on the length or bulkiness of the alkyl group in RNCS. Isomer 2 was favorable for R = Me and Et and exclusive for R = n-Pr, n-Bu, and cyclohexyl. Upon GLC injection (at 150–200 °C), compounds of type 2 isomerized completely to 3 (when R = Me, Et), mostly to 3 and partially decomposed to RN=C=NR (11) (when R = n-Pr, n-Bu), and exclusively decomposed to 11 for R = cyclohexyl. Tertiary RNCS did not yield cyclic products but instead underwent chlorination to substitute a hydrogen (or “NCS” group) by chlorine. Plausible mechanistic schemes are suggested and discussed.