Regioselective Preparation of 1-(Bromomethyl)-5H-thiazolo[3,2-a]quinazolin-5-ones and Analogous 5H-Thieno[3,2-e]thiazolo[3,2-a]pyrimidin-5-ones from Fused 2-(Alkenylthio)pyrimidin-4-ones

Abstract

A convenient procedure for the regioselective preparation of polycyclic angular thiazolo[3,2-a]pyrimidin-5-ones is reported. 2-(Alkenylthio)quinazolin-4(3H)-ones and analogues thieno[2,3-d]pyrimidines were treated with bromine in acetic acid to obtain 1-(bromomethyl)-5H-thiazolo[3,2-a]quinazolin-5-ones 8a,d, and 1-(bromomethyl)-5H-thieno[3,2-e]thiazolo[3,2-a]pyrimidin-5-ones 8b,c,e,f, respectively. A route starting from 2-(alkenylamino)benzamides, which were converted to corresponding 2-thioxoquinazolin-4-ones and subsequently treated with bromine in acetic acid furnished angular 2-(bromomethyl)thiazolo[3,2-a]quinazolin-5-ones 11, or 3-(bromomethyl)[1,3]thiazino[3,2-a]quinazolin-6-ones 14, respectively.