Single-Flask Manganese(I)-Catalyzed Dienylation and Diels–Alder Cascade: Synthesis of Indole–Cyclohexene Hybrids with Anti-Inflammatory Activity

A manganese(I)-catalyzed C-H dienylation of indoles with allenyl benzoate was developed that enables access to C2-dienylated indoles. Moreover, a one-pot consecutive cycloaddition process using a range of dienophiles afforded a series of complex alicyclic scaffolds. Mechanistic experiments demonstrated reversible C-H metalation and a possible five-membered manganacycle intermediate. This manganese-catalyzed dienylation-cycloaddition reaction enables the synthesis of novel indole-cyclohexene conjugates with potential anti-inflammatory activities.