Synthesis of Thieno-Fused Five- and Six-Membered Nitrogen and Oxygen Heterocycles via Intramolecular Heteroannulation of 4,5-Substituted 3-Amino or 3-Hydroxy 2-Functionalized Thiophenes

Abstract

Diverse general high-yield routes for novel thieno-fused five- and six-membered nitrogen and oxygen heterocycles such as thieno[3,2-b]pyrroles, thieno[3,2-b]furans, thieno[3,2-b]indoles, thieno[3,2-b]benzofurans, thieno[3,2-b]pyridine-5-ones, thieno[3,2-b]pyran-5-ones, thieno[3,2-b]isoquinolin-5-ones, thieno[3,2-b]chromen-5-ones, thieno[3,2-b]quinolin-9-ones, and thieno[3,2-b]chromen-9-ones have been developed via in situ or stepwise intramolecular heteroannulation of newly synthesized 4,5-substituted 3-amino- or 3-hydroxy 2-functionalized thiophenes. These substituted 3-amino/hydroxythiophenes were readily obtained in high yields from easily accessible precursors, in a sequential one-pot process, by treatment of a range of (het)aryl/unsubstituted acetonitriles or acetates with (het)aryl dithioesters in the presence of LDA, followed by in situ alkylation-intramolecular condensation of the resulting enethiolate salts with functionalized activated methylene halides. The functionalized activated methylene halides employed in these reactions for the synthesis of various thieno-fused heterocycles were cinnamyl bromide, 2-bromobenzyl chloride, bromocrotonate, 2-(bromomethyl)benzoate, and 2-chlorophenacyl bromide. A few of the 4,5-substituted 3-amino/hydroxy-2-stryrylthiophenes (or 2-acrylates) displayed strong fluorescence, and their absorption/emission spectra have also been examined.