The N-oxides of new heterocyclic systems. Syntheses and chemical properties of thiazolo(4,5-g)quinazoline 3-oxides and thiazolo(5,4-f)quinazoline 3-oxides.

Thiazolo [4, 5-g] quinazoline 3-oxides and thiazolo [5, 4-f] quinazoline 3-oxides, the N-oxides of new heterocyclic systems, were synthesized and their chemical properties were investigated. Namely, the reaction of 7-chloro-1, 3-dimethyl-6-nitroquinazoline-2, 4 (1H, 3H)-dione (1) with methyl thioglycolate in the presence of triethylamine gave 7-methoxycarbonylmethylthio-1, 3-dimethyl-6-nitroquinazoline-2, 4 (1H, 3H)-dione (2) and subsequent treatment of 2 with pyrrolidine resulted in base-catalyzed dehydrative cyclization to afford 2-methoxycarbonyl-6, 8-dimethylthiazolo [4, 5-g] quinazoline-5, 7 (6H, 8H)-dione 3-oxide (3) and 6, 8-dimethyl-2-pyrrolidinocarbonylthiazolo [4, 5-g] quinazoline-5, 7-(6H, 8H)-dione 3-oxide (5). On the other hand, the reaction of 5-chloro-1, 3-dimethyl-6-nitroquinazoline-2, 4 (1H, 3H)-dione (10) with methyl thioglycolate in the presence of triethylamine directly yielded 2-methoxycarbonyl-6, 8-dimethylthiazolo [5, 4-f] quinazoline-7, 9 (6H, 8H)-dione 3-oxide (11). These N-oxides were confirmed to be useful starting materials for the preparation of a variety of thiazolo [4, 5-g]- and [5, 4-f] quinazoline derivatives.