Transition-Metal-Free Activation of Amide Bond by Arynes

Highly reactive arynes activate the N⁻C and C=O bonds of amide groups under transition metal-free conditions. This review highlights the insertion of arynes into the N⁻C and C=O bonds of the amide group. The insertion of arynes into the N⁻C bond gives the unstable four-membered ring intermediates, which are easily converted into ortho-disubstituted arenes. On the other hand, the selective insertion of arynes into the C=O bond is observed when the sterically less-hindered formamides are employed to give a reactive transient intermediate. Therefore, the trapping reactions of transient intermediates with a variety of reactants lead to the formation of oxygen atom-containing heterocycles. As relative functional groups are activated, the reactions of arynes with sulfinamides, phosphoryl amides, cyanamides, sulfonamides, thioureas, and vinylogous amides are also summarized.