Boron tribromide → 2,2-dimethyl-3,4-dihydro-2H-1-benzopyran-7-ol

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Reaction Steps

To a stirred solution of 7-Methoxy-2,2-dimethyl-chroman (4.55 g, 23.7 mmol, from step 1) in anhydrous dichloromethane (50 mL) was added 1M BBr3 (72.86 mL, 47.4 mmol, 2.0 eq) via cannula over 10 min. The resulting dark brown solution was stirred at rt for 17 h. Saturated solution of NaHCO3 (50 mL) was added and extracted with CH2Cl2 (3×50 mL. The combined organic layers were dried over Na2SO4, filtered and evaporated. The residue was purified on silica gel (flash column chromatography) eluting with 5% ethyl acetate-hexane followed by 20% ethyl acetate-hexane to provide the desired product as white solid (1.76 g, 42%). 1H-NMR (CD3CN) δ 6.89 (d, J=8.5 Hz, 1H), 6.68 (broad, s, 1H, OH), 6.31 (dd, J=2.4, 8.5 Hz, 1H), 6.15 (d, J=2.4 Hz, 1H), 2.69 (t, 2H), 1.79 (t, 2H), 1.31 (s, 6H). MS LC-MS (MH+=179).

Provenance & Evidence