Phosphorus tribromide → 3,5-Dimethoxybenzyl Bromide

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Phosphorus tribromide (0.4 eq) was added to the alcohol 304 (25 g, 0.13 mol) in THF (100 mL) very slowly at −10° C. and the mixture which resulted was stirred for 15-30 min at the same temperature. By this time all the starting material had disappeared (TLC). The reaction mixture was quenched by addition of ice-cold H2O (100 mL) and then filtered through a Buchner funnel. The filtrate was diluted with brine (100 mL) and extracted with EtOAc (3×300 mL). The combined organic extracts were dried (Na2SO4) and concentrated in vacuo. The crude oil was purified by FCC (20% ethylacetate in hexane) to afford the bromide 305 as a white solid (92%)a: 1H NMR (500 MHz, CDCl3) δ 6.61 (2H, d, J=2.3 Hz), 6.46 (1H, t, J=2.3 Hz), 4.5 (2H, s), 3.85 (6H, s). 13C NMR (125 MHz, CDCl3): δ 161.3, 140.2, 107.4, 101.0, 55.8, 34.1. The spectral data for 305 were in excellent accord with data previously reported on it (Seidel et al., 1990)1. This material was employed directly in the next step.

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