Using TBS-protected alkyne 6 combined with a one-pot desilylation (HF•py) and basic (NaHCO3) work-up enabled formation of 4 using the more stable alkyne 6. The same response to [Rh] variation was observed (entries 6-9), consistent with 1 and the preceding turnover analysis (Figure ); however, based on the larger steric parameters of OTBS vs. OH, 6 required 20 mol% [Rh] for an efficient reaction vs. 10% for alcohol 1 (entry 1). It should be noted that an excess of diyne and slow addition was required to offset the kinetics of the significantly more facile homodimer-and trimerization of the diyne, consistent with previous studies on this fundamental rate difference (entry 10). The generality of the synthetic process was explored for both protocols, enabling access to a range of novel BOB scaffolds (TBS ether, Method A, Scheme 3a; alcohol, Method B, Scheme 3b). A variety of functional groups were tol-erated including sulfonamides, carbamates, esters, cyclobutyl groups, and bromides. Modification of the hydroxy BMIDA alkyne component allows for the generation of complex systems with oxaborole ring sizes of 5-7, a specific limitation for alternative methodologies. A surprising result was the high regioselectivity observed for 16 and 20: the current doctrine in this area is that sterics govern the regioselectivity of [2+2+2]cycloadditions through kinetic effects; therefore, the isolated regioisomer would be expected to be the minor component; however, the opposite was observed. Several limitations were encountered throughout the scope, which could be rationalized accordingly (Scheme 3c): firstly, due to the increased flexibility of 1,7 diynes (e.g., 30), the formation of the critical intermediate Rh(III) rhodacyclopentadiene is impeded and gave low yield or no reactivity. Due to the sensitivity of the cycloaddition towards sterics, substitution on the diyne (31) and at the propargylic position (32-34) was not well tolerated. The remaining monoalkynes were poorly reactive overall in the [2+2+2]cycloaddition (35, 36).