Changing 2-Br for the iodo-and chloro-analogues (2-I and 2-Cl) delivered moderate yields with greater pinacol speciation to byproduct 4, suggesting that 2-Br had an optimal balance of reactivity and stability to allow effective cross-coupling (entries 5 and 6). As part of efforts to avoid speciation issues, we attempted to use the pinacol ester of 1 (p-tol-BPin, 4); however, interestingly, this was ineffective (entry 7), indicating that 4 does not undergo effective transmetalation under these conditions. Similarly, control experiments (see ESI) indicated benzylic BPin product 3 was unreactive towards transmetalation, eliminating possible oligo/polymerization. These data indicated a chemoselective transmetalation process was operative, where boronic acid 1 was reactive to transmetalation where BPins 2-Br, 3, and 4 were not. While this represents one of the key selectivity elements in the overall process, a consequence of this selectivity is that uncontrolled speciation (conversion of 1 to 4) during the reaction effectively leads to reaction shutdown. It is therefore necessary to control speciation, which can be realized by tuning the nature and stoichiometry of the base and stoichiometry of H2O. This was effectively achieved using 3 equiv K3PO4 with 10 equiv H2O (entry 1). Subtle changes, for example, to K2CO3 led to poorer conversion to desired product 3, with an increase in the transesterification product (entry 8). Other bases, water concentration, and reaction temperature had similar negative effects (see ESI). The generality of the formal homologation was assessed using a broad range of aryl and hetroarylboronic acids (Scheme 2a).