Solvent-free and ball mill-free catalytic C–H methylation

Abstract

An expedient, mechanochemical, operationally simple protocol is reported for the Rh-catalysed C–H methylation of (hetero)arenes under solvent-free conditions without the use of a ball mill. Reagent mixing and activation are delivered using simple pestle-and-mortar grinding and subsequent heating, providing access to the same sustainability benefits as ball milling without the need for specialised equipment. Calculated E-factors are identical to those of ball milling and 5–25 times lower than for solution based conditions. The C–H methylation displays complete regioselectivity and good functional group tolerance. Reaction mixture analyses using scanning electron microscopy and differential scanning calorimetry are described.