Returning to the formation of benzoxaborinines derived from internal alkynes, e.g. 8, in directed electrophilic borylation reactions five membered boracycles are often the kinetic product. Significantly, six membered boracycles are invariably the thermodynamic product for boracycles containing all sp 2 centres. This was confirmed in this case using calculations on a model alkyne 6-Me (Fig. , inset), with 7-Me being 14 kcal mol -1 higher in energy than the six membered isomer 8-Me (at the M06-2x/6-311+G(d,p) level with PCM (CH2Cl2)). Therefore the reaction of 6 and BCl3 was repeated in o-dichlorobenzene (which also led to formation of 7 as the major and 8 as the minor products at room temperature). Pleasingly, heating this reaction mixture to ≥ 140 o C (for several days) led to the isomerization of 7 and formation of 8 as the major product (Fig. .