[C:1]([O:5][C:6]([C:8]1([C:16](=[O:18])[CH3:17])[CH2:13][O:12][C:11]([CH3:15])([CH3:14])[O:10][CH2:9]1)=[O:7])(C)(C)[CH3:2].C(OCC)(=O)CC(C)=O>>[CH2:1]([O:5][C:6]([C:8]1([C:16](=[O:18])[CH3:17])[CH2:9][O:10][C:11]([CH3:14])([CH3:15])[O:12][CH2:13]1)=[O:7])[CH3:2]Compound 99a was prepared in the same manner as 5-acetyl-2,2-dimethyl-[1,3]dioxane-5-carboxylic acid tert-butyl ester using ethyl acetoacetate instead of 3-oxo-butyric acid tert-butyl ester in 31% yield over 2 steps. 1H NMR (300 MHz, CDCl3) δ 1.29 (t, J=7.1 Hz, 3H), 1.40 (s, 3H), 1.44 (s, 3H), 2.33 (s, 3H), 4.23 (q, J=7.1 Hz, 2H), 4.30 (ABq, ΔδAB=0.04, JAB=11.9 Hz, 4H).
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