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.