Palladium-catalyzed synthesis of phenazines via reductive cyclization of 2-nitro-N-phenylanilines with gaseous CO or its surrogates

Phenazines are a diverse class of nitrogen-containing heterocycles with a wide range of chemical structures and biological applications. Our group has pioneered Pd-catalyzed reductive cyclization of nitroarenes using gaseous carbon monoxide [1] or its surrogates [2] as a powerful strategy for N-heterocycles synthesis[3]: in this work we have developed a synthetic route for phenazines starting from 2-nitro-N-phenylanilines using either gaseous carbon monoxide or phenyl formate as an in-situ CO source, as efficient and cheap reductant. Our protocol offers a practical alternative to existing methods, achieving good yields without relying on large amounts of strong reducing or oxidizing agents. Moreover, it minimizes the formation of unwanted by-products, which is a common drawback in traditional phenazine synthesis. The key advantages of this protocol include the use of a very low amount of simple Pd-catalyst in the presence of 1,10-phenanthroline (Phen), an inexpensive and commercially available ligand. These features make our method more practical and accessible for phenazine synthesis.