C[Si](C)(C)N[Si](C)(C)C.[Li].[C:11]([O:15][C:16]([NH:18][C:19]1[CH:23]=[C:22]([CH3:24])[O:21][N:20]=1)=[O:17])([CH3:14])([CH3:13])[CH3:12].S(OC)(O[CH3:29])(=O)=O>C1COCC1>[C:11]([O:15][C:16]([N:18]([C:19]1[CH:23]=[C:22]([CH3:24])[O:21][N:20]=1)[CH3:29])=[O:17])([CH3:14])([CH3:13])[CH3:12]Under an atmosphere of argon, a 1M solution of lithium hexamethyldisilazane in THF (1.1 ml) was added dropwise to a stirred solution of 3-tert-butoxycarbonylamino-5-methylisoxazole (Tet. Lett., 1996, 37, 3339-3342; 0.2 g) in THF (9 ml) that had been cooled to −5° C. After 10 minutes, a solution of dimethyl sulphate (0.1 ml) in THF (1 ml) was added dropwise and the resultant mixture was stirred at −5° C. for 2 hours. The mixture was evaporated and the residue was partitioned between methylene chloride and water. The organic phase was dried over magnesium sulphate and evaporated to give 3-(N-tert-butoxycarbonyl-N-methylamino)-5-methylisoxazole (0.19 g); 1H NMR: (CDCl3) 1.54 (s, 9H), 2.36 (s, 3H), 3.34 (s, 3H), 6.5 (br s, 1H).
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