[CH3:1][Si:2]([CH3:15])([CH3:14])[C:3]#[C:4][B:5]1[O:9][C:8]([CH3:11])([CH3:10])[C:7]([CH3:13])([CH3:12])[O:6]1.[OH:16]/[N:17]=[C:18](\Cl)/[CH3:19].C(=O)([O-])O.[K+]>COCCOC>[CH3:19][C:18]1[C:4]([B:5]2[O:9][C:8]([CH3:10])([CH3:11])[C:7]([CH3:13])([CH3:12])[O:6]2)=[C:3]([Si:2]([CH3:14])([CH3:15])[CH3:1])[O:16][N:17]=1To a solution of trimethyl[(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)ethynyl]silane (240 g, 1.07 mol) in 1,2-dimethoxyethane (8000 mL) was added (1Z)—N-hydroxyethanimidoyl chloride (120 g, 1.28 mol) and potassium hydrogen carbonate (214.4 g, 2.141 mol). The reaction mixture was heated to 50° C. After 16 hours, the reaction mixture was filtered and concentrated under reduced pressure. The residue was purified via chromatography on silica gel (10% ethyl acetate/hexanes, linear gradient) to afford 3-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-5-(trimethylsilyl)isoxazole. MS ESI calc'd. for C13H24BNO3Si [M]+ 281. found 281. 1H NMR (400 MHz, CDCl3) δ 2.39 (s, 3H), 1.31 (s, 12H), 0.37 (s, 9H).
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