Dichloromethane → 2-bromo-7-chloro-9-methylene-9H-xanthene

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Reaction Steps

2-Bromo-7-chloro-9H-xanthen-9-one (prepared as described in example 1 using 4-bromophenol and 2-bromo-5-chlorobenzoic acid) (12.78 g, 41 mmol) was treated with 100 ml of dry THF. The mixture was stirred for 10 min at room temperature and the resulting suspension was placed in water-ice bath for another 10 min. MeMgBr (23 ml, 70 mmol) (3M in THF) was added dropwise under argon using syringe. As addition progressed major amount of solid dissolved to form red solution. The mixture was stirred another 5 min at 0° C. then was removed from the bath and allowed to reach room temperature. The flask was recooled to 0° C. and ˜20 ml of saturated ammonium chloride solution was added dropwise slowly (CAREFUL: gas evolution!). The mixture was diluted with ether, organic layer was separated, washed with brine, dried and concentrated to afford an oil. The oil was dissolved in 100 ml of DCM, PPTS (0.2 g, 0.8 mmol) was added and the mixture was heated to reflux for 5 min and left overnight at room temperature. The precipitate was filtered and rinsed with ether, the filtrate was concentrated in vacuo and treated with hot methanol (˜30 ml) and allowed to crystallize at room temperature. The crystalline material was filtered off and dried in vacuo. These two batches gave 2-bromo-7-chloro-9-methylene-9H-xanthene (8.69 g, 68% yield). m/z=307.5 [M+H]+. Calc'd for C14H8BrClO: 307.5

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