Divergent Assembly of Polycyclic Structures via Cascade Asymmetric Dearomatization of Indoles/Aza-Prins Cyclization/Selective Transformations of Phenonium-like Intermediates

Skeleton rearrangement involving carbocation species is an enabling class of organic transformations. It has found great utility in the synthesis of advanced target molecules with complex structures and hindered stereogenic centers. Regulating the pathways for the transformations of highly reactive carbocation intermediates, such that the skeleton rearrangement takes place in a selective manner, is highly desirable but challenging. Herein we report the divergent assembly of a series of chiral polycyclic molecules based on selective transformations of bridged-ring phenonium-like intermediates that are readily generated via asymmetric electrophilic dearomatization of indoles with o -chloranil/ o -quinone dibenzimides followed by aza-Prins-type cyclization. The initial step of such cascade reactions is promoted by chiral phosphoric acid catalysts, while the downstream generation and transformation of the phenonium-like intermediates are facilitated by additional acid additives. Target molecules with diverse polycyclic structures are obtained in good yields (up to 97%) with high enantioselectivity (up to >99% ee). The energy profiles and asymmetric induction models of these reactions are revealed by comprehensive DFT calculations.