Advancement in the Synthesis of N‐Substituted Phenothiazines

ABSTRACT N‐substituted phenothiazine derivatives are useful heterocycles that are known to have diverse uses in therapeutic agents, electronic devices, and as materials. Earlier approaches for the synthesis of N‐substituted phenothiazines are based on nucleophilic substitution, amine coupling, and other routine organic transformations, which frequently require the utilization of environmentally damaging solvents/agents. The appearance of green chemistry has given rise to another synthetic strategy that aims to avoid the use of hazardous substances and to maximize yield. The green approach has various advantages, including time saving, less usage of solvents, and improved yields. Specifically, microwave‐induced reactions and solvent‐free systems provide higher energy efficiency and purity of the final product. Further, new catalytic methods via green rhodium and palladium catalysts, along with the green solvent Deep Eutectic Solvents, are shown for the synthesis of complex N‐substituted phenothiazine derivatives, including the functionalized forms to improve electron transport and photostability, which are beneficial in the application of the materials. This review seeks to present conventional and green synthetic methodologies for the synthesis of N‐substituted phenothiazine and to point out both the advantages and disadvantages of each; also, to showcase the possible impact of greener advances for the sustainable synthesis of these multifunctional compounds.