Synthesis of tetrahydrocarbazoles through a radical cation [4+2] cycloaddition reaction of 2-vinylindoles.

A redox umpolung strategy for the synthesis of complex tetrahydrocarbazoles is reported. The reaction involves a visible light promoted radical cation [4+2] cycloaddition between 2-vinylindoles and conjugated alkenes that proceeds with good yields and diastereoselectivity.