The borylation proceeds in good yield starting from 3-Br when heated in an open-system, which is essential to facilitate loss of HBr and help drive the reaction to completion. As HNTf2 is not consumed in this reaction, its loading could be reduced (e.g. to 30 mol%) and after 6 h 1-Br is formed in ca. 90% conversion under these conditions (by in-situ NMR spectroscopy). Installation of mesityl onto 1-Br by addition of MesMgBr at 0 °C enabled the isolation of 1-Mes (Scheme 2). 1-Mes is bench stable in solution for at least two months (by 1 H NMR spectroscopy), and displayed a 11B = 39.5 comparable to related benzannulated azaborines. 1-Br also was converted to 1-Ph, however, 1-Ph proved unstable during work up and could not be isolated cleanly. HNTf2 and 4-Br (Scheme 3). Remarkably, this reaction mixture produces azaborine 1-Br at room temperature, with the by-product from SEAr, HBr sequestered by 4-Br to reform 3-Br (under these room temperature closed vessel conditions). The reformed HNTf2 can be used to react with further PhSiMe3 to produce benzene and Me3SiNTf2, the latter reacts with more 3-Br to produce further 4-Br, Me3SiBr and HNTf2 which in turn produces more 1-Br. This cycle can be repeated until all 3-Br is converted into 1-Br, and this was achieved by sequential addition of multiple portions of PhSiMe3 until 1-Br is the major boron containing species (> 90% conversion by in-situ NMR spectroscopy).