Oxidant and Transition-Metal-Free Photoinduced Direct Oxidative Annulation of 1-Aryl-2-(furan/thiophen-2-yl)butane-1,3-diones

Abstract

A photoinduced direct oxidative annulation of 1-aryl-2-(furan/thiophen-2-yl)butane-1,3-diones and ethyl-2-(furan-2-yl)-3-oxo-3-(aryl-2-yl)propanoates in EtOH without the need for any transition metals and oxidants provided access to highly functionalized polyheterocyclic 1-(5-hydroxynaphtho[2,1-b]furan-4-yl)ethanones and 1-(5-hydroxyfuran/thieno/pyrrolo[3,2-e]benzofuran-4-yl)ethanones. The phenomenon of excited-state intramolecular proton transfer (ESIPT) was observed for both 1-(5-hydroxynaphtho[2,1-b]furan-4-yl)ethanone and 1-(5-hydroxy furan/thieno/pyrrolo[3,2-e]benzofuran-4-yl)ethanone analogues.

Catalytic Dehydrogenative Cyclization of o‐Teraryls under pH‐Neutral and Oxidant‐Free Conditions

“…When only 3 mol % of the Co catalyst was used, 35 % yield of triphenylene 2 a was observed (entry 8) and a quantitative yield could still be obtained with a prolonged reaction time (entry 9). Finally, the solvent effect was studied (entries [10][11][12]. Among all solvent screened, MeCN proved to be the most effective.…”

Catalytic Dehydrogenative Cyclization of o‐Teraryls under pH‐Neutral and Oxidant‐Free Conditions

“…However, its use in the cyclodehydrogenation of simple arene substrates is still rare and limited. On the other hand, direct coupling of an organic photochemical process, for example, electrocyclization, (in the absence of photoredox catalysts) with the cobaloxime‐catalyzed hydrogen evolution has not been reported to the best of our knowledge . Given the attractive aspects of having hydrogen as a useful byproduct and the demand for more chemoselective PAH synthesis, we developed a cobaloxime‐catalyzed acceptorless dehydrogenative cyclization of o ‐teraryls under acid and oxidant‐free conditions (Scheme B).…”

Synthesis of2H‐benzo[g]furo/thieno/pyrrolo[2,3‐e]indazolesviaIntramolecular Dehydrogenation Photocyclization

“…Surprisingly, Scheme 2 Synthesis of 2H-benzo[g]furo/thieno/pyrrolo [2,3-e]indazoles and 2H-benzo[g]furo/thieno/pyrrolo [2,3-e]indazols-10-ol via intramolecular dehydrogenation photocyclization dehydration products 3 as a by-product and dehydrogenation products 2 were obtained (Scheme 2). Given our interest in development of strategy to synthesize ploybenzne fused heterocyclic aromatic compounds via photoinduced annulation as well as the existence of limited literature reports on intramolecular dehydrogenative annulation, [23] herein, we would like to report syntheses of 2H-benzo[g]furo/thieno [2,3-e]indazoles and 2H-benzo[g]furo/ thieno/pyrrolo [2,3-e] [2,3-e] indazoles is an environmentalfriendly strategy. Most of the photoinduced cross-dehydrogenative coupling (CDC) reactions needed oxidants or transition metals.…”