Hierarchically Porous Sphere-Like Copper Oxide (HS-CuO) Nanocatalyzed Synthesis of Benzofuran Isomers with Anomalous Selectivity and Their Ideal Green Chemistry Metrics

Abstract

Development of nanocatalysts for a chemical reaction with ideal values in green chemistry metrics is considered to be a challenging task to achieve sustainable chemistry. With this aim, we herein report a hierarchically porous sphere-like copper oxide (HS-CuO) nanocatalyst to afford benzofuranamine and dihydro-benzofuranamine isomers with anomalous selectivity via O-annulated A3 coupling among salicylaldehydes, secondary amines, and alkynes followed by cycloisomerization in the absence of base and solvent. The anomalous selectivity of benzofuran isomers was dependent on the electronic factors of substituents on salicylaldehyde and the type of secondary amines used in the coupling reaction. The HS-CuO nanocatalyst was recycled five times without significant loss in its catalytic activity. The present method offers several advantages over the reported methods such as wide substrate scope with anomalous selectivity in the products, high yields in short reaction time, avoided the usage of extra reagents such as additives/bases, and showed ideal values of green chemistry metrics such as low E-factor and process mass intensity (PMI), high atom economy (AE), reaction mass efficiency (RME), and carbon efficiency (CE).

A Review on Recent Advances in the Application of Nanocatalysts in A3 Coupling Reactions

“…In 2017, Rawat and coworkers investigated the preparation of hierarchically porous sphere‐like copper oxide (HS‐CuO) via thermal decomposition of malachite [Cu 2 CO 3 (OH) 2 ] microspheres into corresponding HS‐CuO (Figure ) . This catalytic system exhibited excellent activity in the preparation of the benzofuran isomers with anomalous selectivity via o ‐annulated A 3 coupling reactions of salicylaldehydes, alkynes and secondary amines followed by cycloisomerization in the absence of base, additive and solvent at 110 °C (Scheme and ).…”

“…It is important to stress that despite huge advancements of the reported works in the literature, another important challenges in the A 3 coupling reactions is nature of solvent and kind of the catalyst. A number of nanocatalysts, including copper, silver, gold, nickel, magnetic nanocatalysts and Co 3 O 4 , ZnS and nanopowder zinc titanate were successfully applied for A 3 coupling reactions with yields ranging from good to excellent in appropriate times in organic solvents or aqueous medium . The authors ascribed high catalytic activity of nanocatalysts to the particles size.…”

Green bio‐based synthesis of Fe2O3@SiO2‐IL/Ag hollow spheres and their catalytic utility for ultrasonic‐assisted synthesis of propargylamines and benzo[b]furans

“…[46] 158-160°C). 1 [28] 9b: Br 3a 5a 10b 35 92 [28] 9c: NO 2 3a 5a 10c 30 93 [30] 9a 3b: ─(CH 2 ) 2 O(CH 2 ) 2 ─ 5a 10d 30 85 [28] 9a 3b 5c 10e 30 88 [30] 9b 3b 5a 10f 25 88 [28] 9c 3b 5a 10 g 20 90 [30] 9c 3b 5b 10 h 30 91 [13] Immobilized silver on surface-modified ZnO nanoparticles Reflux/H 2 O 240 10 mol% 89 [52] Ag-CIN-1 a H 2 O/40°C 720 5 mg 65 [49] Ag I -pc-L b Toluene/MW/150°C 20 3 mol% 59 [50] CuNPs/TiO 2 Neat/70°C 420 0.5 mol% 91 [10] ZnS Reflux/CH 3 CN 270 10 mol% 89 [51] Sulfonate-based cu(I) metal-organic frameworks Reflux/EtOH, 90°C 1440 20 mg 87 [17] CuI catalysts supported on protonated trititanate nanotubes Solvent-free, 70°C 90 20 mg 95 [20] Cu 2 O/nano-CuFe 2 O 4 Solvent-free, 90°C 40 10 mg 93 [18] Copper nanoparticles supported on starch microparticles THF, 60°C 1200 0.3 mol% 95 [21] Cu(II) Schiff base complex immobilized on graphene oxide Water, reflux, N 2 900 20 mg 83 [19] a Ag-grafted covalent imine network material. For the first time, a hybrid magnetic hybrid catalyst, h-Fe 2 O 3 @SiO 2 -IL/Ag, was designed and synthesized through incorporation of [pmim]Cl with h-Fe 2 O 3 @SiO 2 and subsequent immobilization of silver nanoparticles via a biosynthetic approach.…”

“…These heterocycles are important pharmacophores and clinically applied drugs, which are prepared via A 3 coupling reaction followed by intramolecular cyclizations . In this context various catalysts such as CuI nanoparticles and hierarchically porous sphere‐like copper oxide can be applied. Therefore, designing novel and efficient methods for the preparation of these compounds is of great interest.…”

Synthesis of benzofurans from the cyclodehydration of α-phenoxy ketones mediated by Eaton’s reagent

“…Recently, a few methods based on “green” chemistry starting from easily accessible materials have been developed (Scheme 1, Path 2), which involve microwave-aided synthesis, 21–24 electrochemical catalysis, 25,26 and nanoparticle catalysis. 27,28…”