Rh(III)-Catalyzed C–H Activation/Cyclization of Indoles and Pyrroles: Divergent Synthesis of Heterocycles

We report herein a new strategy of the Rh­(III)-catalyzed C–H activation/cyclization of indoles and pyrroles, for the divergent synthesis of privileged heterocycles. A simple derivation of indoles and pyrroles to <i>N</i>-carboxamides with oxidative bidentate directing group could enable rhodacycle formation and late-stage redox-neutral cyclization with alkynes, alkenes and diazo compounds, for access to five- and six-membered fused heterocycles, such as pyrimido­[1,6-<i>a</i>]­indol-1­(2<i>H</i>)-one, 3,4-dihydropyrimido­[1,6-<i>a</i>]­indol-1­(2<i>H</i>)-one, and 1<i>H</i>-imidazo­[1,5-<i>a</i>]­indol-3­(2<i>H</i>)-ones. Kinetic isotope effect study was conducted, and a plausible mechanism was proposed. Furthermore, this protocol was applied to concise synthesis of 5-HT3 receptor antagonist in gram-scale