Stereospecific and Stereodivergent Allyl-Allyl Coupling: Construction of Vicinal Tertiary and All-Carbon Quaternary Stereocenters

Abstract

We demonstrate an iridium-catalyzed highly stereospecific and stereodivergent allyl-allyl coupling between branched allyl carbonates and alpha-silyl-gamma,gamma-dialkyl allylboronic esters. When 3,5-(CF3)2-phenyllithium was used as an activator of the boron group of alpha-silyl-gamma,gamma-dialkyl allylboronic esters, the enantioenriched (E)-1-silyl-substituted 1,5-dienes bearing a tertiary stereocenter adjacent to the all-carbon quaternary center were obtained. Notably, this approach allows access to all four possible stereoisomers by permuting the chirality of the employed alpha-silyl-gamma,gamma-dialkyl allylboronic esters and ligands. Density functional theory calculations provide mechanistic insights into the observed selectivities. Evaluation of transition state energies offers theoretical support for the experimental outcomes and identifies the key factors controlling the chemo-, diastereo-, and enantioselectivity. Furthermore, we demonstrate synthetic applications by transforming the resulting enantioenriched (E)-1-silyl-substituted 1,5-dienes into a variety of enantioenriched compounds, showcasing the versatility of this approach.