Boron trifluoride etherate → 6-(5-Bromo-2-chlorobenzyl)-2,3-dihydrobenzo[b][1,4]dioxine

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To a stirred suspension of 5-bromo-4-methoxy-2-chlorobenzoic acid (128, 4 g, 15.2 mmol) in dichloromethane (100 mL) was added oxalyl chloride (1.6 mL, 18.3 mmol) and DMF (2 drops) at 0° C. and stirred for 2 h. The mixture was concentrated, and the residual colorless solid was dissolved in dichloromethane (100 mL). To this solution were added 1,4-benzodioxane (2 mL, 16.7 mmol) and then AlCl3 (2.23 g, 16.7 mmol) portionwise. After being stirred at room temperature overnight, the mixture was poured into ice water and extracted with dichloromethane two times. The combined organic layers were washed with 1M HCl, water, and brine, then dried over magnesium sulfate, filtered and concentrated in vacuo. The crude residue was diluted with dichloromethane/acetonitrile (35 mL/35 mL) and added triethylsilane (7.4 mL, 45.6 mmol) followed by boron trifluoride diethyl etherate (5.8 mL, 45.6 mmol) at −10° C. The solution was allowed to warm to room temperature over 5 h prior to quenching with saturated sodium bicarbonate solution. After removal of organic volatiles under a reduced pressure, the crude residue was purified by silica gel chromatography (3 to 10% tetrahydrofuran in hexane) to yield the title compound (130, 3.6 g, 9.74 mmol, 64%; 3 steps) as a white solid.

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