Synthesis of indolo[2,1-α]isoquinoline derivatives via metal-free radical cascade cyclization

In the present studies, we describe a convenient and efficient protocol for the synthesis of the indolo[2,1-α]isoquinoline core structure through the reaction of 2-aryl-N-acryloyl indoles and aryl or alkyl α-keto acids under air environment in four hours. The developed approach features broad substrate scope and good functional group tolerance under mild reaction conditions without a metal catalyst participation. A series of valuable indolo[2,1-α] isoquinoline derivatives bearing various functional groups were synthesized using this method in good to excellent yields. Based on a series of control experiments, a radical pathway was proposed to explain the experiment.