Versatile and Sustainable Approach to Access Biologically Relevant Chromeno[2,3-]pyridine and Benzylpyrazolyl Coumarin Derivatives Using Graphitic Carbon Nitride as a Reusable Heterogeneous Catalyst.

Herein, the synthesis of graphitic carbon nitride (g-CN) via the simple heating of cheap and readily available urea as the starting material has been reported. The catalytic activity of the prepared g-CN was investigated for the synthesis of chromeno[2,3-]pyridine and benzylpyrazolyl coumarin derivatives in an ethanol medium. The reactions were performed under mild conditions to achieve widely functionalized target products in a one-pot operation. The as-synthesized g-CN, being a heterogeneous catalyst, demonstrates excellent recyclability up to the 5th consecutive run without a significant decrease in its catalytic activity and yield of the product. A gram-scale reaction was performed to demonstrate the industrial applications of the present protocol. The green chemistry metrics such as environmental factor (E-factor), atom economy (AE), carbon efficiency (CE), and reaction mass efficiency (RME) were calculated and found to be very close to the ideal values. Additionally, operation simplicity, wide substrate scope, easy reusability of the catalyst, and avoidance of metal contamination in the products drive the process toward green and sustainable development.