Synthesis of C4-Substituted Indoles via a Catellani and C–N Bond Activation Strategy

This paper describes the case of a cross study between the C–N bond cleavage reaction field and the Catellani–Lautens reaction system. A series of highly functionalized C4-substituted indoles were synthesized using this strategy. By screening the alkyl groups of amines, the energy barrier of C–N bond cleavage reaction was reduced and the corresponding allenization products were avoided. Finally, the density functional theory calculation shows that the inert C–N bond activation reaction is not a concerted process; on the contrary, the coupling reaction first generates indole quaternary ammonium salt, and then C–N bond cleavage occurs via an SN2 process.