Introducing a methyl group into pyridines and quinolines: A mini-review

Pyridines are ubiquitous N-heterocycles that are present in many natural products and synthetic drugs with important biological applications. Introduction into a pyridine of a methyl (Me) or an isotopically labeled methyl group at carbon can alter its biological properties. However, regioselective introduction of a Me group in high yield, and preferably in a green manner, is often quite challenging. In this mini-review, several methods, most of which are recent, are examined whereby a Me or CD3 is introduced at a specific carbon in pyridines, as well as in some quinolines.