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. - The selective and efficient catalytic C-H methylation of (hetero)arenes is demonstrated without involving solvents or ball milling.