Access to allyl- <i>gem</i> -difluorides <i>via</i> allylation and Cope rearrangement

Fluorinated molecules play crucial roles in medicinal and materials chemistry, as the presence of fluorine profoundly alters molecular electronics and reactivity. Among them, allyl <i>gem</i>-difluorides have attracted growing attention as versatile synthetic intermediates, but their selective construction remains challenging. Here, we disclose an efficient strategy for synthesizing allyl <i>gem</i>-difluorides bearing (<i>E</i>)-vinyl boronic esters through a LiO<i>t</i>Bu-mediated deborylative allylation/Cope rearrangement sequence of 3-boryl-1,1-difluoro allylboronic ester with allyl bromides. Four competing pathways (α-S_N2, α-S_N2', γ-S_N2, and γ-S_N2') were identified: α-addition generates intermediates that undergo Cope rearrangement, while γ-addition directly delivers the same products. Mechanistic studies, supported by control experiments as well as NBO and FMO analyses, demonstrate a synergistic effect between the 1,1-difluoro group and the boronic ester that lowers the activation barrier of the rearrangement. This transformation displays broad substrate scope and provides versatile building blocks for the construction of allyl <i>gem</i>-difluorides.