Synthesis of heterocyclics via enamines. VI. Acid-catalysed transformation of 4,6,6-Trimethyl-3,6-dihydropyrimidine-2-thiols. Functionalized cyclic enamines

Abstract

On heating with HCl or H₂SO₄, 4,6,6-trimethyl-3-phenyl-3,6- dihydropyrimidine-2-thiol (1; R = Ph) formed phenylthiourea and 4,6,6- trimethyl-2-phenylamino-6H-1,3-thiazine (3; R = Ph) and not 4,4,6- trimethyl-2-phenylamino-4H-1,3-thiazine (2; R = Ph) as reported by Ignatova. In a similar reaction, 4,6,6-trimethyl-3,6-dihydropyrimidine- 2-thiol gave thiourea, 2-amino-4,6,6-trimethyl-6H- 1,3-thiazine (3; R = H) and 4,6,6-trimethyl-4-(4',4',6'-trimethyl-1',4'-dihydropyrimidin-2'-ylthio)-tetrahydropyrimidine-2(1H)-thione (9).