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Step 4: 8-Bromo-4-methylenechroman (P34d)To a stirred mixture of PPh3CH3Br (25.4 g, 71.1 mmol) in dry THF (250 mL) was added /T-BuLi (2.5M, 28.5 mL, 71.3 mmol) under N2 at -40C and the mixture was stirred for 30 min at that temperature. Then a solution of compound P34c (8.0 g, 35.6 mmol) in dry THF (80 mL) was added dropwise. The solution was stirred at rt for 2 h, then quenched with aq. NH4CI at 0C and extracted with EA. The organic layer was concentrated and purified by CC (PE/EA = 50/1) to give P34d (5.2 g, 66%) as an oil.
Step 3: 8-Bromochroman-4-one (P34c) The solution of compound P34b (2.0 g, 8.15 mmol) in ethylene glycol (20 mL) was heated at reflux for 4 h. The reaction mixture was cooled, poured into water and extracted with Et20 twice. The combined organic layers were combined, washed with 1 M aq. NaOH and sat. ammonium carbonate, dried over Na2S04, filtered, concentrated and purified by CC (PE/EA = 50/1) to give compound P34c (0.88 g, 48%) as a yellow solid.
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