Iridium-catalyzed doubly stereoconvergent allylic alkylation of racemic α-boryl organozinc reagents

Transition-metal-catalyzed allylic alkylation of α-boryl metallic reagents has provided unique access to chiral homoallylic organoboron compounds. However, these organoboron products possess only one stereogenic center, which is derived exclusively from either allylic electrophiles or gem-diborylalkanes. The construction of contiguous stereocenters from both α-boryl metallic reagents and allylic electrophiles has remained elusive. We report a straightforward method to prepare secondary α-monoboryl organozinc reagents through α-deprotonation of benzylboronates and in situ Li/Zn exchange that was then applied in the iridium-catalyzed allylic alkylation reaction through a doubly stereoconvergent process. Various boron-containing 1,2-stereodiads were obtained in good yields with decent diastereo- and enantioselectivities. Compared to the deborylative allylic alkylation using gem-diborylalkane, this study demonstrates high atom economy and a wide substrate scope. A preliminary mechanism study demonstrated that the stereoconvergent and kinetic resolutions of racemic carbonates proceed simultaneously.