The benzyne cycloaddition strategy to construct the AB ring (Scheme 2) commenced with esterification of 12 and MOM protection of the phenol to afford 13 in 90% yield over the 2 steps. Magnesium-halogen exchange and trapping with trimethyl borate gave boronic acid 14, which was carried forward without purification due to its insolubility. MOM deprotection and formation of the boronic ester delivered 15, which was characterized and isolated in a 65% yield over the three-step sequence. Formation of the benzyne triflate precursor 10 proceeded smoothly in 82% yield. In situ formation of the benzyne utilized the Turbo Grignard iPrMgCl•LiCl; trapping with furan 11 gave 16 as the major regioisomer in 60% yield (10.1:1 rr), plus a small amount of a minor regioisomer 16a (not shown). The inseparable OBD regioisomers were carried forward into the next step. Scheme 2. Synthesis of OBD intermediate 9. Oxidation of the boronic ester of 16 with urea hydrogen peroxide (UHP) and separation of the desired OBD regioisomer 17 was followed by methylation of the phenol to furnish 9 in 77% yield over the two steps. This oxidationmethylation strategy proved advantageous, as removal of the boronic ester rendered purification of the later intermediates much easier and a free phenol could later be easily accessed for the B ring.