Diazo Quinone: An Effective Phenolic Precursor for Building C(sp2)-C(sp2) Bonds

Phenolic biaryl and styryl moieties are important structural motifs in natural products, pharmaceuticals, and functional materials. Traditional cross-coupling often requires pre-functional substrates and is accompanied by generation of organometallic by-products. In recent years, diazo quinone has become a new type of high-efficiency phenolic coupling reagent for the preparation of phenolic biaryl and styryl compounds. This is because it can be used to construct C(sp(2))-C(sp(2)) bonds in an environment-friendly (transition-metal-free) or more direct way. In this review, we focus on recent advances in the field of transition-metal-free cross-coupling reactions of diazo quinones with organoboranes and transition-metal catalyzed quinoid carbene C(sp(2))-H arylation reactions.