Visible light-driven strategies for the synthesis of pyrazole scaffolds: needs, mechanistic insights and sustainable horizons

Abstract

Pyrazoles constitute an important class of five-membered N-heterocyclic frameworks associated with numerous applications as pharmaceuticals, agrochemicals, bioactive compounds and functional materials. Their existing synthetic methods are associated with various disadvantages, such as the use of strongly acidic or basic conditions, high temperatures, and metal-based catalysts. Therefore, the demand for environmentally safe and economical strategies to overcome the existing challenges in synthetic organic chemistry has intensified significantly. In recent years, photoredox catalysis has revolutionized organic synthesis, particularly in the development of different types of heterocycles. Visible light-driven photocatalysis (VLPC) has gained considerable attention and emerged as a clean, energy-efficient, eco-friendly, sustainable, and selective approach for various organic transformations, aligning with the principles of green chemistry and sustainable development goals. Therefore, in view of the importance of pyrazoles and photocatalysis, this article focuses on the recent progress in the visible light-driven synthesis of pyrazoles. It highlights the importance of greener and sustainable protocols involving different substrates under mild reaction conditions using various light sources, such as compact fluorescent lamps (CFLs) and white, green, or blue light-emitting diodes (LEDs). The mechanistic aspects of these reactions have also been discussed. The shift towards such methods not only aligns with the green and sustainable chemistry principles but also reduces the environmental impact of constructing pyrazole frameworks and functional materials. We believe that this review will inspire researchers to explore more innovative, eco-friendly, and sustainable synthetic pathways for synthesizing such heterocycles in the future.