Several heterocycles were well tolerated including thiophenes (39-41), pyridine (42), furans (43, 44), and isoxazole (45). Some limitations of the boronic acid scope included specific functional groups (46, 47), heterocycles (48, 49), styrene boronic acid (50), and alkylboronic acids (51). In general, unprotected heteroatoms/coordinating groups were recalcitrant across the scope assessment based on robustness screen evaluation (see ESI). Standard reaction scale was 0.2 mmol; however, reactions were effective at 2.5, 5 and 10 mmol scale (examples 42, 15, and 6, respectively). A series of investigations were undertaken to explore the reactivity of the halomethyl BPin reagent and to understand key limitations (Scheme 3). Regarding the enhanced electrophilicity of the C-Br bond imparted by the proximity of the boryl unit, Matteson approximated a ~300-700-fold increase in reactivity in nucleophilic substitution reactions. Under the catalytic conditions above, the effect of the boron unit is immediately apparent from control and competition experiments. In comparison to several different bromide-derived electrophiles, 2-Br has similar reactivity to bromobenzene and benzyl bromide in comparative Suzuki-Miyaura couplings with 1 (Scheme 3a). This was supported by competition experiments between 2-Br and (pseudo)halobenzenes where 2-Br was significantly more reactive than chlorobenzene and benzene trifluoromethylsulfonate, less reactive than iodobenzene, and exhibited similar reactivity to bromobenzene (Scheme 3b). Control reactions indicated lack of reactivity under Gevorgyan's conditions and performing the reaction in light or dark had no influence. In attempts to determine if the boryl unit can influence reactivity at greater distances from the C-B bond, we endeavored to examine the ethyl and propyl homologues (Scheme 3c). Unfortunately, 1,2-bromoethyl BPin could not be prepared via any approach attempted by us and external suppliers (see ESI); however, 1,3-bromopropyl BPin could be obtained (see ESI) but was unreactive to the coupling with 1. The reaction was found to be highly sensitive to the ester diol (Scheme 3d). Any change from the BPin was detrimental -poor to moderate yields were observed only with propan-1,3-diol derivatives, with no product observed in any other case and this did not seem to track with established general stability of the boronic esters to protodeboronation; however, the lack of reactivity of 61 and 67 was perhaps expected based on previous understanding of stabilities of the aboryl radicals. Otherwise, these effects are unclear. Finally, substitution on the methylene was not tolerated, restricting the reaction to a single unsubstituted methylene homologation: no reactivity was observed with 68-71 (Scheme 3e). This lack of reactivity was found to be due to sluggish oxidative addition. NMR investigations established that 2-Br undergoes smooth oxidative addition while no oxidative addi-tion is observed when substitution was introduced to the methylene (see ESI). Attempts to improve oxidative addition with 68-71 by variation of reaction conditions and ligand/precatalysts were unsuccessful (see ESI). In summary, a formal homologation of arylboronic acids has been developed based on the use of bromomethyl BPin as carbenoid equivalent. The process allows for the direct synthesis of relatively rare benzylic boronic acid esters from aryl boronic acids without the use of organometallic reagents. Control experiments have provided information on the reactivity identified in this system, which support enhanced oxidative addition enabled by proximity to the C-B bond and a highly specific reactivity and stability profile of the halomethylboronic acid pinacol ester.