Facile reaction of carboxylic acids with isonitriles in toluene

Isonitriles react with low concentrations of carboxylic acids in toluene at 110 °C to give N-formylamides in yields generally above 70%. These concentrations can be obtained either by syringe pump addition of a toluene solution of the acid, or by using a suspension of the acid if it has limited solubility in toluene at room temperature.