The Synthesis of 4-Hydroxydithiocoumarins: A Case of Unusual Tautomer Stability

Abstract

2'-Chloroacetophenones react with carbon disulfide in the presence of sodium hydride to form 4-hydroxydithiocoumarin anions. Kinetic protonation provides the 4-hydroxydithiocoumarins which can be tautomerized to 2-mercapto-1-thiochromones by treatment with strong acid.   Both tautomers are quite stable and do not readily interconvert. Alkylation of either 4-hydroxydithiocoumarin or 2-mercapto-1-thiochromone provides S-alkyl derivatives exclusively while acylation with acid anhydrides gives mixtures of O- and S-acyl products. Oxidation with sodium perborate yields the exocyclic monosulfoxide while m-chloroperbenzoic acid gives the exocyclic sulfone.