Novel synthesis of angular thiazolo[5,4-f] and [4,5-h]quinazolines, preparation of their linear thiazolo[4,5-g] and [5,4-g]quinazoline analogs

Synthesis of 9-oxo-8,9-dihydrothiazolo[5,4-f]quinazoline-2-carbonitrile (1) or 6-oxo-6,7-dihydrothiazolo[4,5-h]quinazoline-2-carbonitrile (2) was reinvestigated with the ambition of varying the position of the thiazole ring linked to the quinazolin-4-one moiety, in order to synthesize two novel linear tricyclic 8-oxo-7,8-dihydrothiazolo[4,5-g]quinazoline-2-carbonitrile (3) and 8-oxo-7,8-dihydrothiazolo[5,4-g]quinazoline-2-carbonitrile (4). The routes described in this paper open the door to various substitutions and transformations for an access to libraries of potent biologically active heterocyclic compounds.