Synthesis of heterocyclics via enamines. I. Formation of 1,4-Dihydropyrimidine-2-thiols and 2-Amino-1,3-thiazines in reactions of ethyl β-aminocrotonates with β-keto isothiocyanates: role of solvents

Abstract

Ethyl β-aminocrotonate (1) on condensation with the β-keto isothiocyanate (2; R = Me) in hexane, benzene, or toluene formed the 1,4-dihydropyrimidine-2-thiol (3; R = Me) as the major product and the 2-amino-1,3-thiazine (4; R = Me) as the minor component. The use of ether, acetonitrile, butan-2-one, ethyl acetate, chloroform as solvents reversed the product ratio. In the reaction with (2; R = Et), the yields of (3 and 4; R = Et) formed were similarly affected by change of solvent.