Efficient and Regioselective Synthesis of Phenothiazine via Ferric Citrate Catalyzed C-S/C-N Cross-Coupling

Efficient C-S and C-N cross-coupling reactions have been developed for regioselective, scalable and environmentally benign synthesis of substituted phenothiazine derivatives. Cross-coupling reactions were demonstrated on various challenging substrates using non-toxic, highly economical, readily available ferric citrate as a catalyst to get desired product with high regioselectivity. Atom economy is the added advantage of this protocol since additional N-protection step before coupling and eventual deprotection of the same to obtain the desired product arenot required. To the best of our knowledge, this is the first report on the use of inexpensive ferric citrate as a catalyst without involving any ligand for the synthesis of regioselectively substituted phenothiazine.