[CH3:1][Si:2]([CH3:15])([CH3:14])[C:3]#[C:4]B1C2CCCC1CCC2.[CH3:16][C:17]([CH3:21])([CH3:20])[CH:18]=[O:19].C(OCC)C.C(CN)O>CCCCC.CO>[CH3:16][C:17]([CH3:21])([CH3:20])[CH:18]([OH:19])[C:4]#[C:3][Si:2]([CH3:1])([CH3:14])[CH3:15]Dissolve B-(2-(trimethylsilyl)ethynyl)-9-borabicyclo[3.3.1]nonane.tetrahydrofuran complex (2.13 g, 7.3 mmol) in pentane (25 mL) and add trimethylacetaldehyde (795 μL, 7.3 mmol). Stir at room temperature for 5 days. Remove the solvent under a positive nitrogen pressure to give a yellow solid. Add ethyl ether (30 mL) and methanol (500 μL). Cool to 0° C. and add, by dropwise addition, ethanolamine (440 μL, 7.3 mmol). Stir overnight, centrifuge the reaction mixture and separate the clear supernatant liquid. Wash the precipitate with pentane (2×10 mL) and combine the organic phases. Wash with water (2×25 mL) and dry (MgSO4). Evaporate the solvent in vacuo and purify by silica gel chromatography (19:1 hexane/ethyl acetate) to give the title compound as a clear liquid (1.25 g, 93%).
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