An optimization study (Table ) revealed that controlling the order of addition and performing the reaction in an open system under N2 enabled formation of 2-Cl from 1a in good conversion (by in-situ NMR spectroscopy versus an internal standard), without requiring a base and using commercial BCl3 solutions. The reaction proceeded in a range of robust (to BCl3) weakly coordinating solvents such as, chlorobenzene, heptane (note 2-Cl precipitated during synthesis in heptane) and trifluorotoluene, but for ease of in-situ analysis and work-up CH2Cl2 was the only solvent used hereon. Post formation of 2-Cl an aqueous work-up led to isolation of the boronate 3a in good yield. Compound 3a displays the expected 11B at 27.2 and 1H resonances at 8.17 (B-OH) and 6.36 (vinylC-H) in d6-acetone. Under identical conditions combinations of 1a and BBr3 led to a comparable outcome and formation of 4a on work up in good isolated yield (78 %). As BCl3 has improved functional group tolerance relative to BBr3, only BCl3 was utilized hereon. It should be noted that 3a can be isolated on 5 mmol scale in 85% yield without any column chromatography. This highlights the simplicity of this procedure to form benzoxaborinines at ambient temperature using 1M BCl3 solutions. With optimized conditions in hand a substrate scope study was performed. Substituents at all four positions on the benzene unit were tolerated (3b-3e), with 3e demonstrating that di-substituted precursors are also viable substrates. Alongside fluoride (3b), this process tolerated chloride (3c) and bromide (3d) which were not reported in the previous nickel catalyzed method to form benzoxaborinines. 1c and 1d have an electron withdrawing group meta to the alkyne (meta + = 0.40 and 0.41, respectively), thus have a less nucleophilic alkyne (than 1a), nevertheless both these substrates undergo trans-haloboration at room temperature to afford the desired products in good yield. The advantage of using BCl3 is demonstrated by the ability to generate benzoxaborinines containing functional groups that would undergo side-reactions with more electrophilic boranes (e.g. BBr3), this includes MeO (3h), an enolisable ketone (3i), CF3 (3j) and an ester (3k). The good (for an electrophilic borylation process) functional group tolerance is attributed to the lower (compared to BBr3) electrophilicity of BCl3 and the fact that haloboration occurs rapidly at room temperature in most cases. It should be noted that 1j, with a CF3 para to the alkyne was the least reactive alkyne in this study, taking 12 h at room temperature to reach high conversion to 3j (Fig. ).