Hydrochloric Acid → 2-t-Butyldimethylsilyl-3-formyl-6-methoxybenzofuran

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Reaction Steps

To a solution of 2-t-butyldimethylsilyl-3-(t-butyldimethylsilyloxymethylene)-6-methoxy-benzofuran (1.09 g, 2.69 mmol) in methanol (100 mL) was added concentrated hydrochloric acid (200 μL) and the reaction was stirred for 30 minutes (monitored by tlc), quenched with triethylamine (2 mL) and the solvent removed by distillation under vacuum. The residue was dissolved in dichloromethane (20 mL), washed with water (10 mL), dried over magnesium sulfate, concentrated under vacuum and co-distilled with toluene (20 mL); 1H NMR (300 MHz, CDCl3) δ 7.57 (d, 1H, J=8.57 Hz), 7.00 (d, 1H, J=2.17 Hz), 6.86 (dd, 1H, J=8.55, 2.22 Hz), 4.81 (s, 2H, CH2), 3.84 (s, 3H, OMe), 0.94 (s, 9H), 0.37 (s, 6H). The crude yellow paste (˜985 mg) was dissolved in dry dichloromethane (4 mL) and added to a stirred solution of Collin's reagent (chromium trioxide (1.01 g), pyridine (1.65 mL) in dry dichloromethane (30 mL)). The suspension was stirred for 10 minutes, filtered and the residue washed with diethyl ether (20 mL). The filtrate was concentrated onto silica (10 g) and purified by flash chromatography (silica gel, eluent=hexane/diethyl-ether/triethylamine (90:9:1) to afford the title compound as a light yellow oil which crystallized on standing (485 mg, 68%);

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