Triisopropyl borate → (4-(Tert-butoxycarbonyl)-2,3,4,5-tetrahydrobenzo[f][1,4]oxazepin-7-yl)boronic acid

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Reaction Conditions

Reaction Steps

A solution of 1,1-dimethylethyl 7-bromo-2,3-dihydro-1,4-benzoxazepine-4(5H)-carboxylate (30.0 g, 91.4 mmol) and triisopropyl borate (22.4 g, 119 mmol) in THF (300 mL) was cooled to −78° C., and a 2.5 M solution of n-butyllithium in hexanes (47.6 mL, 119 mmol) was added dropwise over 40 min at this temperature. The reaction mixture was stirred at −78° C. for an additional 30 min, then quenched by dropwise addition of 2 N hydrochloric acid (80 ml), and allowed to warm up to room temperature. Ethyl acetate (100 mL) and water (100 mL) were added, the organic layer was separated, and the aqueous layer was extracted with ethyl acetate (100 mL). The combined organic layers were washed with water, dried over sodium sulfate, and concentrated. Hexane (200 mL) was added to the residue and the mixture was stirred overnight. The precipitate was filtered, washed several times with hexane, and dried to give (4-{[(1,1-dimethylethyl)oxy]carbonyl}-2,3,4,5-tetrahydro-1,4-benzoxazepin-7-yl)boronic acid (23.4 g, 87%) as a colorless solid. MS (EI) for C14H20BNO5: 294 (MH+).

Provenance & Evidence