Catalytic oxidative carbon–carbon bond-formations of benzene-1,2-diols

Abstract The cross-dehydrogenative coupling (CDC) reaction has emerged as a powerful synthetic tactic for forging carbon–carbon bonds starting from two nucleophiles. However, the mechanisms underlying this reaction class are complex and not always intuitive. Thus, understanding the key principles to selectively promote the bond-forming event in each CDC reaction is a prominent step for the further development of these reactions. Herein, we focus on the CDC reaction of benzene-1,2-diols (catechols and pyrocatechols), aiming to make the complex bond-forming event more comprehensive. To draw mechanistic views, we divide the reaction types according to the mechanistic difference in the C–C bond-forming event: In the Type I mechanism, the reaction is initiated by oxidation of benzene-1,2-diols to the corresponding 1,2-benzoquinones. In the Type II mechanism, the coupling partner is initially oxidized, and the resulting radical directly couples with benzene-1,2-diols (or their enolate form). According to this mechanistic classification, we first describe the basic features of the quinone redox reaction to discuss the reactivity difference between benzene-1,2-diols and 1,2-benzoquinones. We then present the historical background and state of the art of current CDC reactions starting from benzene-1,2-diols. This mini-review encourages the development of catalytic CDC reactions of benzene-1,2-diols and other substrates.