Enantio-, Regio-, and E-Selective Hydroboration of 1,3-Dienylsilanes to Construct Bifunctional Allylation Reagents.

Double-allylation reagents serve as powerful linchpins for assembling two electrophiles, such as aldehydes. Although great advances have been made in the construction of achiral double-allylation reagents, the catalytic enantioselective synthesis and application of linear 1,3-bifunctional allylborons remain rarely developed. Herein, we report a copper-catalyzed enantio-, regio-, and E/Z-selective hydroboration of 1,3-dienylsilanes to afford bifunctional allylation reagents bearing a chiral center at the allylic position. The kinetic resolution process of the E/Z-mixture of dienylsilanes ensures high ee of products regardless of the initial E/Z-ratio. Density functional theory (DFT) studies were conducted to probe the origins of the enantio- and E/Z-selectivities. Sequential allylation of aldehydes with the newly developed double-allylation reagents can construct chiral 3,6-dihydropyrans and pent-2-ene-1,5-diols bearing four contiguous stereocenters with excellent diastereoselectivities and enantioselectivities.