RGO/ZnO nanocomposite: an efficient, sustainable, heterogeneous, amphiphilic catalyst for synthesis of 3-substituted indoles in water

A nanocomposite consisting of reduced graphene oxide and zinc oxide nanoparticles (RGO/ZnO) with unique structural features was developed as an efficient, sustainable, amphiphilic, heterogeneous catalyst for the synthesis of various 3-substituted indoles in water. The catalyst was recycled six times without significant loss in catalytic activity. The higher environmental compatibility and sustainability factors such as smaller E-factor and higher atom economy make the present methodology a true green and sustainable process for the synthesis of various biologically important 3-substituted indoles

Reduced Graphene Oxide Supported Copper Oxide Nanocomposites from a Renewable Copper Mineral Precursor: A Green Approach for Decarboxylative C(sp³)–H Activation of Proline Amino Acid To Afford Value-Added Synthons

A green approach for decarboxylative C­(sp³)–H activation of proline amino acid was accomplished by coupling with aldehydes and alkynes to afford α-alkynylated N-substituted pyrrolidines as value-added synthons using reduced graphene oxide supported copper oxide (RGO@CuO) nanocatalysts. The RGO@CuO nanocomposites were obtained by the impregnation of micrometer-sized malachite spheres, as a renewable and sustainable copper mineral precursor, on the graphene oxide (GO) sheets followed by calcination at 300–450 °C for 5 h. The characterization of as-synthesized composites revealed the generation of monodispersed and uniformly embedded copper oxide (CuO) nanoparticles with sizes ranging from 10 to 15 nm on RGO thin sheets via GO as a support as well as indirect template for dissembling and decomposition of micrometer-sized malachite spheres. The RGO@CuO composites were found to be efficient and robust nanocatalysts compared with CuO nanoparticles (NPs) alone. The present method offers several advantages, such as wide substrate scope, and avoids the usage of excess equivalent of substrates with minimal waste generation (E-factor = 0.24) and high reaction mass efficiency (80.7%), and the nanocatalyst was recycled for five times without significant loss in its activity with a negligible leaching of CuO NPs from RGO sheets

Hydromagnesite Rectangular Thin Sheets as Efficient Heterogeneous Catalysts for the Synthesis of 3‑Substituted Indoles via Yonemitsu-Type Condensation in Water

The anisotropic controlled assembly of nanobuilding blocks into uncommon uniform rectangular thin sheet morphology of hydromagnesite (RS-HM) with a high surface area of 110 m²/g was achieved by a simple conventional heating under green reaction condition. The synthesized RS-HM was calcined at 450 °C in the presence of air and resulted in the formation of MgO with a surface area 120 m²/g. RS-HM was found to be a more efficient catalyst than MgO for the synthesis of novel 3-substituted indoles via Yonemitsu-type condensation selectively in excellent yields. The present method has advantages such as environmentally benign, ease to handle, selectivity and excellent yields, low <i>E</i>-factor (0.15) and high atom economy (96%)

Decarboxylative Coupling Strategy To Afford <i>N</i>‑Heterocycles Driven by Silica-Nanosphere-Embedded Copper Oxide (Cu@SiO₂‑NS)

An environmentally benign and surfactant-free method was developed for the preparation of porous silica nanospheres (SiO₂ NS) from the hydrolysis of tetraethoxyorthosilicate (TEOS), using corn starch as a sacrificial template. The stabilization of malachite on SiO₂ NS, followed by calcination at 600 °C, afforded silica-nanosphere-embedded copper oxide (Cu@SiO₂-NS). The obtained Cu@SiO₂-NS was found to be a versatile nanocatalyst for the decarboxylative coupling strategies to afford aromatic or aliphatic <i>N</i>-heterocycles such as aminoindolozines, pyrrolo­[1,2-<i>a</i>]­quinolones, and substituted pyrrolidine. The Cu@SiO₂-NS was successfully recycled for six times without significant loss in its catalytic efficiency. The present method shows several advantages, such as being an environmentally benign approach for the catalyst preparation, being easy to handle, and having a wide substrate scope for decarboxylative couplings with excellent yields in short reaction time, and showed excellent green chemistry metrics, such as E-factor, process mass intensity (PMI), reaction mass efficiency (RME), carbon efficiency (CE), and comparatively high turnover number/turnover frequency (TON/TOF) values