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

Abstract

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 N-heterocycles such as aminoindolozines, pyrrolo­[1,2-a]­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.

CuII@PAA/PVC mesoporous fibers: A hybrid wedding as a high‐performance versatile heterogeneous catalyst for A3, KA2, and decarboxylative A3 reactions

“…As shown in Figure , the binding energies of Cu 2p in the fresh (Figure a) and recovered catalyst (Figure b) were measured to be 932.8 eV and 953.1 eV. These results indicated that the presence of Cu II species in both freshly prepared and recovered catalyst …”

“…These results indicated that the presence of Cu II species in both freshly prepared and recovered catalyst. [19][20][21]44] The SEM images of PAA/PVC and Cu II @PAA/PVC shown in Figure 4 were recorded at low (200 nm) and high magnifications (100 nm) for easy clarity and comparison. The visible rough surface with porous can be observed for PAA/PVC hybrid fibers (image a, and b).…”

“…In the decarboxylative A 3 couplings, alkynyl carboxylic acids act as economical and stable surrogate for terminal alkynes via extrusion of CO 2 in situ. Thus, a number of homogeneous catalysts such as CuI, CuBr, CuCl 2 /CuI, CuI/Cu(OTf) 2 , and heterogeneous catalysts including Cu(II)/HM, CuO/Fe 2 O 3 NPs, Cu@SiO 2 ‐NS, and chit@copper have been used in decarboxylative A 3 coupling reactions.…”

Recent Advances on Diverse Decarboxylative Reactions of Amino Acids

“…Rawat et al. reported a green and sustainable approach for the decarboxylative tandem coupling of proline 205 , 3‐nitrobenzaldehyde 451 , and phenylacetylene or phenyl propionic acid 452 to afford aliphatic nitrogen heterocycles such as 1‐benzyl‐2‐(phenylethynyl)pyrrolidine 453 using a Cu nanocatalyst (Cu@SiO 2 ‐NS) (Scheme ) …”

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

“…Transition metal-catalyzed decarboxylative coupling reaction provides an ecofriendly pathway for C–C or C–heteroatom bond formation due to in situ formation of organometallic species. − This involves relatively neutral conditions and eliminates expensive and toxic organometallic reagents. , Various decarboxylative Csp 3 –Csp 3 , Csp 3 –Csp 2 , and Csp 3 –Csp couplings − have been reported to synthesize a wide range of value-added chemicals including propargylamines, biaryls, , 2-alkynylbuta-1,3-dienes, 1,4-diamino-2-butynes, 1,2,3-triazoles, etc. Recently, we reported decarboxylative A3 and KA2 coupling strategies for one-pot multicomponent reactions to afford a wide range of propargylamines and C1-alkynylation of tetrahydroisoquinolines and N-heterocycles using CuO@Fe 2 O 3 MNPs and Cu@SiO 2 –NS as recyclable nanocatalysts, respectively. , To date, there are very few reports describing the decarboxylative tandem coupling among proline, aldehydes, and alkynes using Cu-salts as homogeneous catalysts. − There is a need to develop efficient nanocatalysts for these decarboxylative tandem coupling reactions under green and sustainable conditions. In this context, we herein report RGO@CuO nanocatalyzed decarboxylative tandem coupling among proline, aldehydes, and alkynes with equimolar ratios yielding a wide range of substituted pyrrolidines with minimum waste generation and high reaction mass efficiency under green reaction conditions (Scheme ).…”