Replicating the Resconi reaction for a baseline, the C-H borylation of 1-methyl-1H-indole with B(C6F5)3 was monitored by 1 H NMR spectroscopy that revealed conversion to the borylated indolinium A after 5 days (120 h) with an isolated yield of 85% (87% conversion, Table , entry 1), half the time from their report with comparable yield (88%). Switching the solvent from CH2Cl2 to benzene had little effect, only a meager decrease in conversion (85% conversion, entry 2). The sluggish reaction may be from either the Lewis acid strength or steric bulk of B(C6F5)3. Switching to the less bulky secondary borane HB(C6F5)2 (% buried volume = 47) presents the possibility of hydroboration or dehydrogenative borylation reactivity. When HB(C6F5)2 was treated with 1-methyl-1H-indole in CH2Cl2 or benzene, it did not lead to any reaction at all (B) even after heating to 80 °C (entries 3 and 4). This implies reducing the electrophilicity has a deleterious effect on the reaction. Replacing B(C6F5)3 with the stronger Lewis acid BoCb3 resulted in no conversion in either CH2Cl2 or benzene, even after heating to 80 °C (entries 5 and 6). This is presumably due to the larger steric profile of the borane (% buried volume of BoCb3 = 72, B(C6F6)3 = 59). Switching to HB Me oCb2, a secondary borane with a smaller steric profile than BoCb3 (% buried volume = 64) and higher electrophilicity than B(C6F5)3, gave encouraging results. Carrying out the reaction with HB Me oCb2 in CH2Cl2 at 23 °C resulted in 37% conversion after 24 h, but in benzene, quantitative conversion is achieved within an hour enabling isolation of 1 in 97% yield (entries 7 and 8, respectively). The structure of 1 was confirmed by a single-crystal X-ray diffraction study (Fig. ).