Synthesis of heterocycles via enamines. Part 12. Intramolecular additions of nucleophiles to 1,4-dihydropyrimidine-2(3H)-thione derivatives: single-step synthesis of condensed heterocyclic compounds

Abstract

In a single-pot operation, 4-isothiocyanotobutan-2-one (9; R¹= H, R²= Me), and functionalised amines, viz. 2-aminoethanol, 2-aminoethanethiol, ethane-1,2-diamine, o-aminophenol, o-aminothiophenol, and propane-1,3-diamine provide the corresponding oxazolo-, thiazolo-, imidazolo-pyrimidines and pyrimido-benzoxazole, -benzothiazole, and -pyrimidines respectively. It is proposed that the intermediate 1-substituted 1,4-dihydropyrimidine-2(3H)-thiones (10) undergo base-catalysed intramolecular addition of the nucleophile at their enamine α carbon, i.e. at C-6.3-Isothiocyanatobutanal (9; R¹= Me, R²= H) reacted similarly with functionalised amines.