Annulation of the Quinazoline Ring Utilizing Mesoionic Ring Systems

Article abstract of DOI:10.1021/jo00210a021

anhydro-3-Hydroxythiazolo<3,2-c>quinazolin-4-ium hydroxides, prepared from the corresponding thioglycolic acid with cyclodehydrating agents and also from 4(3H)-quinazolinethiones and α-bromophenylacetyl chloride, were hydrolyzed at the 5-position of the quinazoline ring with hot water.Alkynic and alkenic dipolarophiles cycloadded readily in hot benzene; the former gave pyrido<1,2-c>quinazolines and the latter 1:1 cycloadducts which lost H2S to give the above ring system.These procedures provided convenient annulation of a pyridinone to the c side of quinazoline.With ethyl acrylate, in addition to the normal 1:1 cycloadduct, a rearranged pyrrolo<1,2-c>quinazoline was obtained depending on the reaction conditions; analogous products were obtained with dimethyl fumarate. anhydro-1-Hydroxythiazolo<3,2-a>quinazolinium hydroxides, preferably generated in situ from the corresponding thioglycolic acid and dicyclohexylcarbodiimide (DCC), and alkynic dipolarophiles in refluxing benzene readily gave pyrido<1,2-a>quinazolines.Alkenic dipolarophiles also gave 1:1 cycloadducts, which lost H2S to form pyrido<1,2-a>quinazolines, resulting in annulation of a pyridinone ring to the a side of quinazoline.