A new chiral Brønsted acid, generated in situ from a chiral phosphoric acid boron (CPAB) complex and water, was successfully applied to asymmetric indole reduction. This "designer acid catalyst", which is more acidic than TsOH as suggested by DFT calculations, allows the unprecedented direct asymmetricreduction of C2-aryl-substituted N-unprotected indoles and features good to excellent enantioselectivities
We have developed a highly efficient and practical strategy for the kinetic resolution of indoline derivatives, involving a chiral Brønstedacid-catalyzed iminium ion formation and asymmetric transfer hydrogenation cascade process. The kinetic resolution allows the synthesis of 2-substituted N-benzylindolines in good yields with moderate to excellent enantioselectivities.