Synthesis of Benzothienobenzofurans via Annulation of Electrophilic Benzothiophenes with Phenols

Abstract

We have developed a metal-free, mild, and green synthetic route toward benzothieno­[3,2-b]­benzofurans by the annulation of 3-nitrobenzothiophene with phenols. The reaction was found to be general with a range of substituted phenols. In addition, we could extend the methodology for the synthesis of pentacenes and could demonstrate the synthesis in gram-scale. Moreover, we extended the strategy for the synthesis of benzothieno­[2,3-b]­benzofurans by starting from 2-nitrobenzothiophenes.

Base-Mediated Annulation of Electrophilic Benzothiophene with Naphthols and Phenols: Accessing Benzothiophene-Fused Heteroacenes

“…In Scheme , we have proposed a mechanism for the present base-mediated annulation of electrophilic benzothiophene with naphthols and phenols by taking 1a and 2a as representative examples. , The annulation starts with the addition of 2-naphthol via the carbon on the 3rd position of naphthol to generate the adduct A . Next, the intermediate B is formed by an intramolecular cyclization of A from the oxygen end of naphthalen-2­(3 H )-one to the C-2 of benzothiophene.…”

“…16 Motivated by these literature precedents and due to our curiosity in the reactivity of electrophilic benzannulated heterocycles, 17 recently we developed a general methodology for the synthesis of benzothieno- [3,2-b]benzofuran from 3-nitrobenzothiophene and phenols. 18 We hypothesized that the other positional isomer, benzothieno [2,3-b]benzofuran, could be made by starting with 2-nitrobenzothiophene. In our original communication, we demonstrated the synthesis of one benzothieno[2,3b]benzofuran example, and in this full paper, we report our whole investigations in developing a synthetic method for hitherto unknown benzothieno [2,3-b]naphthofurans and benzothieno [2,3-b]benzofurans.…”

“…A report for the synthesis of substituted furans from nitrostyrenes with 1,3-dicarbonyl compounds or phenols by Hajra and co-workers caught our singular interest . Motivated by these literature precedents and due to our curiosity in the reactivity of electrophilic benzannulated heterocycles, recently we developed a general methodology for the synthesis of benzothieno­[3,2- b ]­benzofuran from 3-nitrobenzothiophene and phenols . We hypothesized that the other positional isomer, benzothieno­[2,3- b ]­benzofuran, could be made by starting with 2-nitrobenzothiophene.…”

Inverse Electron Demand Diels Alder Reaction of Aza-o-Quinone Methides and Enaminones: Accessing 3-Aroyl Quinolines and Indeno[1,2-b]quinolinones

“…Due to our continued interest in devising methodologies toward heteroarenes and inspired from the report on Pd-catalyzed dual C–H activation of 3-phenoxypyridine-1-oxides, we planned to utilize 3-aroyl quinolines to synthesize rarely known indeno­[1,2- b ]­quinoline-11-ones . We started with the N -oxidation of 3-aroyl quinolines with mCPBA, and the obtained quinolinyl- N -oxides were directly taken for the Pd-catalyzed dual C–H activation after optimization (Table ).…”

Copper-mediated construction of benzothieno[3,2-b]benzofurans by intramolecular dehydrogenative C–O coupling reaction

“… 31 Most recently, John group have developed a mild metal-free synthetic route toward BTBFs by the annulation of 3-nitrobenzothiophene with phenols ( Scheme 1f ). 32 However, all these methods required metal catalysts or harsh conditions, and multistep transformations for the synthesis of BTBFs with limited scopes.…”