N-bromosuccinimide (10.7 mg, 0.06 mmol) and concentrated H2SO4 (5 μL) were added to a solution of 2 (15.4 mg, 0.044 mmol) in THF (1 mL). The solution was stirred at room temperature for 20 h, and then diluted with EtOAc (30 μL). The same workup and purification procedure as described for the isolation of 37 gave 38 (12 mg, 64%) as a pale yellow powder. mp 256° C. (decomp.); 1H NMR (CDCl3) δ 8.89 (s, 1H, H4), 7.65 (s, 1H, H6), 6.76-6.91 (m, 3H, H2′+H5′+H6′), 6.08 (AB, 2H, 3′,4′-OCH2O—, Δδ=8.7 Hz, J=1.5 Hz), 5.97 (AB, 2H, 7,8-OCH2O—, Δδ=7.8 Hz, J=1.5 Hz), 5.22 (q, 2H, lactone-CH2—, J=8.4 Hz); MS (EI) m/z 428 [M+2]+, 426 [M]+.
