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

Abstract

The construction of benzothieno[3,2-b]benzofurans via novel dehydrogenative C–H/O–H coupling reaction has been developed with excellent yields. Furthermore, three-to-six fused ring thienofuran compounds could be constructed.

Cu‐catalyzed dehydrogenative CO arylation for the synthesis of 6‐methyl benzofuro[3,2‐c] quinoline derivatives

“…When ligands O-Phenanthrene and X-Phos were added, no significant change was observed in yield (Table 1, entries [16][17]. Moreover, when this transformation was performed in the absence of a catalyst or base no progression in reaction was found (Table 1, entries [18][19], which implies that both catalyst and base play an extensive role in supervisory of the reaction.…”

“…Furthermore, K. Mitsudo and S. Suga group (Scheme 2) independently reported the synthesis of furan‐fused thienoacenes using Cu‐catalyzed dehydrogenative CO arylation [17]. Moreover, in 2021, B. Li and co‐workers (Scheme 3) developed copper‐mediated construction of benzothieno [3,2‐ b ] benzofuran by intramolecular CO coupling [18]. Taking clues from the above strategies through copper metal catalysis, we are tempted to synthesize 6‐methyl benzofuro[3,2‐ c ] quinoline through intramolecular dehydrogenative CO coupling, employing copper as a catalyst (our work, Scheme 4).…”

Synthesis and Applications of Benzothienobenzofurans: A Review

“…Very recently, Li and co-workers introduced another method for the construction of benzothieno[3,2-b]benzofurans by a copper mediated intramolecular dehydrogenative CÀ O coupling reaction (Scheme 16). [28] This approach constitutes an improved version of the work reported by the same authors on the intramolecular Ullmann coupling of 2-(3-bromobenzothiophen-2-yl)phenols. [18] The substrates for the present methodology, 2-(benzo-thiophen-2-yl)phenol derivatives 56 were synthesized by the Suzuki coupling of functionalized 2-bromobenzothiophenes and 2-hydroxyphenylboronic acids.…”

“…The method was found to be general for the synthesis of a range of substituted benzothieno The authors conducted control experiments and found that the reaction proceeded by a radical pathway (Scheme 17). [28] Based on these observations, they have proposed a mechanism starting with the generation of the phenoxide anion 57 by the action of the base on (benzo-thiophen-2-yl)phenol 56. Next, a single electron transfer takes place between 57 and Cu(OAc) 2 yielding the phenoxy radical 58 which undergoes a intramolecular cyclization to afford the radical intermediate 59.…”

Emerging Trends in Copper-Promoted Radical-Involved C–O Bond Formations

“…Related O -centered radicals, such as phenoxy radicals, generated from phenols via base-assisted copper-mediated oxidation, have also been exploited to prepare polycyclic oxygen-containing compounds through intramolecular dehydrogenative C–O coupling . Moreover, a range of easily accessible N -hydroxylamines, such as N -hydroxyphthalimides, N -hydroxybenzotriazoles, and N -hydroxamic acids, have also been identified as competent precursors to O -centered radicals and can engage in an array of copper-mediated intermolecular O -centered radical addition/coupling reactions (Scheme d).…”