Domino reactions of cyclic enaminones leading to selective synthesis of pentacyclic indoles and its functionalization

A new multicomponent domino reaction of cyclic enaminones with acenaphthylene-1,2-dione in an anhydride solvent has been established, providing selective protocol to pentacyclic indoles with different substituted patterns (up to 50 examples). Both substitutions on the cyclic enaminone ring and reaction temperatures showed obvious impact on the reaction pathways. For instance, selective allylic hydroxylation and allylic esterification of in situ generated indoles depend on reaction temperatures. With special substituents, the reactions underwent dehydrogenation process to give access to different substituted fused indoles with good to excellent yields. These reactions feature mild conditions, convenient one-pot operation and short reaction times. The purification of products only needs to be washed by 95% ethanol without traditional chromatography and recrystallization, which characterizes group-assisted purification (GAP) chemistry.