Tandem Allylation/1,2-Boronate Rearrangement for the Asymmetric Synthesis of Indolines with Adjacent Quaternary Stereocenters.

Abstract

A three-component coupling using lithiated indoles, boronate esters and allylic acetates generates chiral indolines with adjacent quaternary stereocenters. Successful stereocontrol required the use of phosphoramidite ligands not previously described for organopalladium chemistry. Mechanistic studies indicate a monodentate PdL intermediate, and a stepwise allylation-aryl/alkyl migration. A protodeborylation strategy was used to install a C-H bond in place of the C-B bond. A photoredox coupling was used to replace C-B bond with a C-C bond in a highly diastereoselective manner. In the specific case of methyl-vinyl ketone, a novel radical-mediated annulation provides polycyclic products with high enantio- and diastereoselectivity.