Stereospecific\nand Stereodivergent Allyl–Allyl\nCoupling: Construction of Vicinal Tertiary and All-Carbon Quaternary\nStereocenters

We demonstrate an iridium-catalyzed highly stereospecific\nand stereodivergent\nallyl–allyl coupling between branched allyl carbonates and\nα-silyl-γ,γ-dialkyl allylboronic esters. When 3,5-(CF<sub>3</sub>)<sub>2</sub>-phenyllithium was used as an activator of the\nboron group of α-silyl-γ,γ-dialkyl allylboronic\nesters, the enantioenriched (<i>E</i>)-1-silyl-substituted\n1,5-dienes bearing a tertiary stereocenter adjacent to the all-carbon\nquaternary center were obtained. Notably, this approach allows access\nto all four possible stereoisomers by permuting the chirality of the\nemployed α-silyl-γ,γ-dialkyl allylboronic esters\nand ligands. Density functional theory calculations provide mechanistic\ninsights into the observed selectivities. Evaluation of transition\nstate energies offers theoretical support for the experimental outcomes\nand identifies the key factors controlling the chemo-, diastereo-,\nand enantioselectivity. Furthermore, we demonstrate synthetic applications\nby transforming the resulting enantioenriched (<i>E</i>)-1-silyl-substituted\n1,5-dienes into a variety of enantioenriched compounds, showcasing\nthe versatility of this approach.