Desilylative allylation of 3,3-borylsilylpropene under metallaphotoredox catalysis

Chemoselective functionalization of hetero-gem-dimetalloid represents an attractive strategy in terms of diversity-oriented synthesis. In particular, desilylative functionalization of gem-silylboronate esters remains a challenging task and existing solutions heavily relied on ionic reactions. Herein, we report a desilylative functionalization of allylic gem-silylboronate esters with aldehydes under synergistic photoredox and chromium(II) catalysis. With different substrates, both α- and γ-functionalization are realized with exclusive regioselectivity and diastereoselectivity, which is dictated by the chair-like transition state of predominant isomer of Cr^III allyl intermediate. Moreover, γ-functionalization products bearing CF₂ unit are acquired when gem-difluoroalkene-containing substrates are employed. In the presence of chiral ligand, enantioselective allylation of aldehydes is successfully accomplished, affording alkenylated 1,2-diols after oxidative workup with excellent regio-, diastereo- and enantioselectivity. The current protocol displays wide substrate generality and broad functional group compatibility. In addition, diverse post-transformations converted obtained products into a variety of valuable structures.