Design and Catalytic Asymmetric Construction of Axially Chiral 3,3'-Bisindole Skeletons.

The first catalytic asymmetric construction of 3,3'-bisindole skeletons bearing both axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2-substituted 3,3'-bisindoles with 3-indolylmethanols (up to 98 % yield, all >95:5 d.r., >99 % ee). This reaction also represents the first highly enantioselective construction of axially chiral 3,3'-bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho-position of prochiral 3,3'-bisindoles. This reaction not only provides a good example for simultaneously controlling axial and central chirality in one operation, but also serves as a new strategy for catalytic enantioselective construction of axially chiral 3,3'-bisindole backbones from prochiral substrates.