Trimethyl borate → (7-Chloro-2,3-dihydrobenzo[b][1,4]dioxin-5-yl)boronic acid

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Reaction Steps

To a stirred solution of 5-bromo-7-chloro-2,3-dihydro-benzo[1,4]dioxine (Preparation 22, 1.5 g, 6 mmol) in dry Et2O (45 ml) under nitrogen at −70° C. was added n-butyl lithium (2.63 ml of a 2.5M solution in hexane, 6.6 mmol) and the resultant mixture stirred for 1 hr. Trimethyl borate (0.92 ml, 8 mmol) was then added and the mixture stirred at room temperature overnight. Saturated aqueous NH4Cl was added (60 ml) and the aqueous layer extracted with Et2O (3×100 ml). The combined organic extracts were concentrated in vacuo. The residue was taken up in 1M aqueous NaOH and washed with Et2O (100 ml). The aqueous layer was then acidified with 2N aqueous HCl (pH 2) and extracted with diethylether (3×100 ml). The organic extracts were combined, dried (MgSO4), filtered and concentrated in vacuo to afford the desired product as a white solid (1.12 g, 87%).

Provenance & Evidence