Transition-metal-free Sonogashira-type coupling of ortho-substituted aryl and alkynyl Grignard reagents by using 2,2,6,6-tetramethylpiperidine-N-oxyl radical as an oxidant.

Cross coupling of aryl, alkenyl, and alkynyl magnesium compounds by using 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) as an environmentally benign organic oxidant is described. This coupling reaction can be performed without adding any transition metal on various ortho-substituted aryl and alkynyl Grignard reagents. Importantly, functional groups such as esters, amides, and cyanides are shown to be tolerated under the reaction conditions.