5-Chlorobenzoxazole → Benzo[D]oxazol-5-ylboronic acid

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A mixture of 5-chlorobenzoxazole (0.129 g, 0.84 mmol), 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi-1,3,2-dioxaborolane (0.4956 g, 1.95 mmol), potassium acetate (0.41 g, 4.2 mmol), 1,3-bis(2,6-diisopropylphenylimidazol-2-ylidene hydrochloride (43 mg, 0.10 mmol) and palladium acetate (11 mg, 0.05 mmol) was degassed, treated with tetrahydrofuran (10 mL) and the resulting mixture heated at 80° C. overnight. The mixture was diluted with water (100 mL), acidified to pH 6 and extracted with EtOAc (3×40 mL). The extracts were washed with water, dried and concentrated in vacuo. The residue so obtained was purified by chromatography over silica gel eluting with DCM to 10% MeCN/DCM to afford 1,3-benzoxazole-5-boronic acid, pinacol ester. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.37-1.39 (m, 12 H) 7.59 (d, J=8.34 Hz, 1 H) 7.86 (dd, J=8.08, 1.01 Hz, 1 H) 8.10 (s, 1 H) 8.26 (s, 1 H); MS (ES+): m/z 246.23 [MH+].

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