Azines and azoles: CXXIX. Synthesis, structure, and some reactions of 2-aryl-4-sulfanyl-6H-1,3-thiazin-6-ones

Abstract

Reactions of 2-aryl-4-chloro-6H-1,3-thiazin-6-ones with sodium sulfide in aqueous alcohol at 18–20°C led to the formation of a readily separable mixture of 2-aryl-4-sulfanyl-6H-1,3-thiazin-6-one sodium salts (yield >70%) and bis(2-aryl-6-oxo-6H-1,3-thiazin-4-yl) sulfides ( 90%) regardless of the alkylating agent, solvent, temperature, reactant concentration, and their ratio. 2-Aryl-4-sulfanyl-6H-1,3-thiazin-6-ones in the crystalline state and in solutions in polar and nonpolar protic and aprotic solvents exist preferentially as 4-sulfanyl-6-oxo tautomers, and they undergo almost complete ionization in neutral aqueous, alcoholic, and aqueous-alcoholic media (pK a = 4.3). Reactions of 4-sulfanyl-2-phenyl-6H-1,3-thiazin-6-one with ammonia, amines, and difunctional N-centered nucleophiles involve cleavage of the C6-S bond in the thiazine ring and subsequent recyclization of linear intermediates to pyrimidines and diazole derivatives. The structure of the isolated compounds was confiirmed by 1H and 13C NMR, IR, and UV spectra.