Synthesis of fused heterocyclics

Abstract

The thesis consists of two parts. Investigations on quinolinoquinolines are embodied in the first part, and investigations on (C3)quinazolones are embodied in the second part. Preceding the two parts, there is a brief general introduction on heterocycles. In the first introductory chapter, all the known quinolinoquinolines have been briefly reviewed. In the second chapter, the synthesis of 6,7-dimethoxy-4-oxo-1,2-dihydro-quinolino[3:2, f3']quinoline — starting from vanillin and through o-nitro-veratraldehyde, diethyl (5-nitroveratrylidene)-malonate, ethyl 6,7-dimethoxy-2-hydroxyquinoline-3-carboxylate, and ethyl 6,7-dimethoxy-2-anilino-3-carboxylate — which was undertaken with a view to clearing up some structural uncertainties present in the work of Arnold Reissert on the quinolino[2,3:8',3']quinoline system, is described. This has helped in suggesting correct structures for some of the quinolino[2,3:8',3']quinolines isolated by Reissert. By modifying Kefford’s method, a more elegant procedure for the synthesis of 6,7-dimethoxy carbostyril has been arrived at. In the first chapter, which is introductory in nature, general methods of preparation and the importance of quinazolones are described. In the second chapter, the synthesis of five new ?-phenylethyl quinazolones has been described. They were synthesized with a view to building quinazolino-isoquinolinium salts, possibly having activity. Attempts at synthesizing quinazolino-isoquinolinium salts were, however, unsuccessful. An attempt at synthesizing isoquinolino[2,3:3',2']quinazoline-4 has resulted in the synthesis of 2-methyl-3-benzyl-quinazolone-4 and 2-formyl-3-benzyl-quinazolone-4, the former showing properties at variance with the reported ones. The results have been discussed. Some Mannich-condensation products of 2-methyl-quinazolone-4 have been described, and their structures discussed. An interesting phenomenon of debenzylation and demethylation has been observed in the hydrochlorides of 2-methyl-3-benzyl-quinazolone-4 and 2,3-dimethyl-quinazolone-4, respectively. By studying the behaviour of the hydrochlorides of three more substituted quinazolones, debenzylation and demethylation have been attributed to water of crystallization present in the hydrochlorides of the quinazolones.