Difluorocyclopropanation of alkenyl trifluoroborates using TMSCF 3 -NaI system was reported for the first time. The developed method allowed preparation of monocyclic, spiroand fused-bicyclic gem-difluorocyclopropanes bearing addi-groups. [20][21][22][23][24] Nonetheless, the addition of difluorocarbene equivalent derived from TMSCF 3 to alkenylboronic derivatives was unknown until the present study. Scheme 1. Difluorocyclopropanation of alkenylboronic derivatives.In this work, application of TMSCF 3 -NaI system in refluxing THF (66°C) for the synthesis of gem-difluorocyclopropyl boronic derivatives and its effectiveness for multigram scale synthesis is reported (Scheme 1). It is shown that alkenyl trifluoroborates are optimal substrates for the preparation of aliphatic derivatives which facilitate isolation of the target products. The studied reaction scope included substrates bearing secondary N-Boc protected amine, ester, ether, phenyl and cyclopropyl moieties and provided products with spiro-and fused-bicyclic molecular topologies. Results and DiscussionOur study commenced with testing TMSCF 3 -NaI system in reaction with substrate 5a (Scheme 2), for which the difluorocyclopropanation using XCF 2 CO 2 Na (X = Cl, Br) at 180°C and 150°C, Scheme 2. Attempted difluorocyclopropanation of alkenyl boronic derivatives using the TMSCF 3 -NaI system. 2218Scheme 3. Preparation of trifluoroborate salts 7 from pinacolboronates 9.Scheme 4. Synthesis of pinacolboronates 9e (A) and 9p (B).