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

5 years ago

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

Vibha Gautam, Anand Acharya, Hiriyakkanavar Ila

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.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b01153

DOI: 10.1021/acs.joc.7b01153