Tautomerism and Regioselectivity of Acylation of 4-Hydroxy-2-mercaptopyridine-N-oxide and 2,4-Dimercaptopyridine-N-oxide: A Computational Study

Abstract

Relative thermodynamic stability and dipole moments of tautomers of 2-mercapto- (1), 4-hydroxy-2-mercapto- (2), 2,4-dimercapto- (3), 4-hydroxy- (4), and 4-mercapto- (5) pyridine-N-oxides were calculated in gas phase at the B3LYP/6-31G(d,p) level of theory. According to the calculations, the general trend in stability of the tautomers follows 2-thiono > 4-thiono/keto > N-oxide. A similar trend is observed in monoacetyl (6 and 7) and diacetyl (8 and 9) derivatives of 2 and 3. Therefore, monoacetylation of 2 or 3 is expected to give the 4-acetyl derivatives and diacetylation the 1,4-diacetyl isomers as the thermodynamic products.