[CH2:1]([O:3][C:4]([C:6]1([C:9]#[N:10])[CH2:8][CH2:7]1)=[O:5])[CH3:2].[CH3:11][C:12](O)([CH2:14][CH:15]([OH:17])[CH3:16])[CH3:13]>S(=O)(=O)(O)O>[CH2:1]([O:3][C:4]([C:6]1([C:9]2[O:17][CH:15]([CH3:16])[CH2:14][C:12]([CH3:13])([CH3:11])[N:10]=2)[CH2:8][CH2:7]1)=[O:5])[CH3:2]To concentrated sulfuric acid (102 mL) was added 1-cyano-cyclopropanecarboxylic acid ethyl ester (60 g, 0.43 mol) dropwise followed by 2-methylpentan-2,4-diol (52 g, 0.44 mmol) dropwise at 0° C. The mixture was stirred for an additional 1 h at 0° C. then poured onto ice-water. The aqueous phase was washed with AcOEt (3×200 mL) and then basified to pH 12 with 10 M NaOH. The resulting mixture was extracted with EtOAc (3×500 mL). The combined organic layer was washed with brine, dried over Na2SO4 and concentrated. The residue was purified by column chromatography on silica gel to give 1-(4,4,6-trimethyl-5,6-dihydro-4H-[1,3]oxazin-2-yl)-cyclopropanecarboxylic acid ethyl ester (65 g, yield: 63.2%). 1H NMR (CDCl3 400 MHz): δ4.21-4.06 (m, 3H), 1.73-1.69 (m, 1H), 1.40-1.10 (m, 17H).
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