[C:1]1([C@@H:7]2[C:11]([CH3:13])([CH3:12])[O:10][C:9](=[O:14])[NH:8]2)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.C([Li])CCC.[C:20](Cl)(=[O:25])[C:21]([CH3:24])([CH3:23])[CH3:22].C(OCC)(=O)C>O1CCCC1>[CH3:22][C:21]([CH3:24])([CH3:23])[C:20]([N:8]1[C@H:7]([C:1]2[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=2)[C:11]([CH3:12])([CH3:13])[O:10][C:9]1=[O:14])=[O:25]Reaction of the auxiliary (15) (0.155 g, 0.81 mmol) in solution in tetrahydrofuran at -78° C. with butyllithium (1.0M, 0.819 ml, 0.821 mmol) and pivaloyl chloride (0.110 ml, 0.89 mmol) for 30 minutes and then at room temperature for 3 hours with work-up and flash column chromatography using 20% ethyl acetate/40-60 petroleum ether as eluant furnished the title compound (22) as an oil (0.128 g, 57%); νmax (CHCl3) 1687 and 1775 cm-3 ; [α]D25 (c 0.4 in CHCl3)=-60.3; (Found: C, 69.94; H, 7.84; N, 4.93. C16H21 NO3 requires C, 69.80; H, 7.69; N, 5.09%); δH (CDCl3 ; 300 MHz) 0.98 (3H, s, C(CH3)2), 1.39 (9H, s, C(CH3)3), 1.60 (3H, s, C(CH3)2), 5.11 (1H, s, CHPh), 7.14-7.37 (5H, m, ArCH; δC (125 MHz; CDCl3) 23.66 (CH3), 26.20 (CH3), 28.68 (CH3), 41.63 (C), 69.03 (CH), 81.80 (C), 126.10 (ArCH), 128.44 (ArCH), 128.85 (ArCH), 136.80 (C), 153.50 (CO), 178.00 (CO); m/z (CI+, NH3) 276 (M+ +1).
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