Organocatalytic Enantioselective Dearomatization of 2,3‐Disubstituted Indoles with α ‐(3‐Indolyl)propargylic Alcohols

This work presents an efficient strategy for the dearomatization of 2,3‐disubstituted indoles to access chiral indole imine‐tetrasubstituted allene skeletons. The transformation is achieved through a chiral phosphoric acid‐catalyzed 1,6‐conjugate addition with alkyne 3‐methylene‐3H‐indoles, generated in situ from α ‐(3‐indolyl) propargylic alcohols. A series of chiral compounds possessing both axial and central chirality were synthesized in good to high yields with high asymmetric induction. Supported by control experiments, a plausible mechanism is proposed to elucidate the reaction pathway.