Synthesis of heterocyclic compounds via enamines. Part 8. Acid-catalysed transformations in 4,4,6-trimethyl-1,4-dihydropyrimidine-2(3H)-thione derivatives and related compounds

1-Substituted 4,4,6-trimethyl-1,4-dihydropyrimidine-2(3H)-thiones (2) on heating in 11M-HCl at 100–110° are converted into the corresponding 2-substituted-amino-4,6,6-trimethyl-6H-1,3-thiazines (4) and/or thioureas. But at 95–100°, Dimroth rearrangement products, e.g, the corresponding 2-substituted-amino-4,4,6-trimethyl 4H-1,3-thiazines (3) are formed.