Recent Progress in Palladium Catalysed Sustainable Synthesis of Heterocycles

Palladium metal has been extensively used in the synthesis of organic molecules for the last few decades. Heterocyclic ring synthesis being a significant part of organic synthesis, transition metal catalysis, especially catalysis by palladium, has been actively employed in heterocyclic synthesis. However, since palladium is an expensive metal, there has always been an urge to reuse or recycle the palladium catalyst to make the process economically viable. Modern synthetic chemists are also in constant search for newer sustainable strategies for molecular synthesis, which will lead to eco-friendly synthetic protocols. Thus, in the last few years, palladium catalysed green synthesis of heterocycles has gained importance as these aim to make the synthetic organic chemical world slightly more sustainable. This review comprises palladium catalysed synthetic strategies that proceed in a sustainable fashion. A few protocols included here involve either organic solvent-free or greener solvents as reaction medium, which is one of the modes adopted towards sustainability. Other modes of sustainability included in this review are recyclability of the palladium catalyst, one pot tandem reaction strategy, use of air as oxidant, etc. All these modes aim at achieving one or the other green chemistry principles like reduction of waste and by-products, increasing atom economy, reduction of cost and use of safer solvents. The review aims to reflect the scope of sustainability in palladium catalysed synthesis of heterocycles so that economically and environmentally viable synthetic methodologies may be selectively identified and applied in academia and industries. Keeping the principles of green chemistry in mind, in this review, we aim to compile the recent advancements in palladium catalysed sustainable synthesis of heterocycles in a single platter that may serve as a piece of reliable literature for further research in this area.