Quinazoline-4-thiones: formation and reaction with hydrazine hydrate

Abstract

2-(Methylthio)quinazoline-4(3H)-thione was synthesized by the reaction of the corresponding 4-oxo quinazoline with Lawesson’s reagent (LR). 2-(Methylthio-4-thioxoquinazolin-3-yl)acetate was obtained in a similar way, while (4-oxoquinazolin-3-yl)ketones reacted with LR to give a mixture of thionation products – (4-thioxoquinazolin-3-yl)ketones and [1,3]thiazolo[2,3-b]quinazoline-5-thiones. Alkylation of 2-(methylthio)quinazoline-4(3H)-thione with chloroacetone, ω-bromoacetophenone or ethyl bromoactate gave the corresponding 4-S-substituted derivatives, which in the reaction with hydrazine hydrate afforded 2-methylthio-4-hydrazinoquinazoline. Methyl (2-methylthio-4-thioxoquinazolin-3(4H)-yl)acetate with hydrazine hydrate under appropriate conditions underwent the heterocyclization reaction to form the 6-methylthio-2H-[1,2,4]triazino[4,3-c]quinazoline system.