Reactivity of condensed thiophenes in the Diels-Alder reaction: The reactivity of 3-aminothieno [3,4:3',4'] benzo [b] pyranone; 3-aminothieno [3,4-c] quinoline and of 5-amino-7-substituted thieno [3,4-d] pyridazinone toward electron-poor olefins and acetylenes

Article abstract of DOI:10.1016/0040-4020(96)00689-8

The thieno [3,4:3',4'] benzo [b] pyranone (3b) and the thieno [3,4-c] quinoline (3c) are prepared via reacting 4-methylcoumarin-3-carbonitrile (9a) and 4-methyl-2-oxo-1,2-dihydroquinolin-3-carbonitrile (9b) with elemental sulphur, Similarly the thieno [3,4:3',4'] naphtho [1,2-b] pyran (11) is prepared from reaction of (10) and elemental sulphur. The condensed thiophenes (3b,c) and (11) react with a variety of electronpoor olefins to yield products of addition followed by hydrogen sulphide elimination. The reaction of (3b,c) and (11) with ethyl propiolate in refluxing dioxane/acetic acid mixture affords the condensed thiepins (24a,c). The nature of product of reaction of (3b,c) and (11) with dimethyl acetylenedicarboxylate is dependent on applied reaction conditions. Thus the reaction of (3b,c) and (11) with dimethyl acetylenedicarboxylate in refluxing dioxane afforded condensed thiepins while at 250°C products of addition and desulfurization are obtained. Whereas thienopyridazinones (1a,b) react with ethyl acrylate and diethyl fumarate to yield thiadiazaacenaphthenones (31a-c) respectively, compounds (1a,b) react with N-phenylmaleimide to yield phthalazine (32). The thienopyridazinone (1c) failed to react with the same reagents under similar conditions.