Transition-Metal-Free Sonogashira-Type Coupling of <i>ortho</i>-Substituted Aryl and Alkynyl Grignard Reagents by Using 2,2,6,6-Tetramethylpiperidine-<i>N</i>-oxyl Radical as an Oxidant

Abstract

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.