[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:24])/[CH:21]=[CH:22]/[CH3:23].C(OCC)(=O)C>O1CCCC1>[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:24])/[CH:21]=[CH:22]/[CH3:23]Reaction of the auxiliary (15) (0.416 g, 2.19 mmol) in solution in tetrahydrofuran (10 ml) at -78° C. with butyllithium (1.3M, 1.69 ml, 2.20 mmol) and crotonyl chloride (0.229 ml, 2.40 mmol) for 30 minutes and then at room temperature for 2 hours, with work-up and flash column chromatography using 20% ethyl acetate/40-60 petroleum ether as eluant furnished the title compound (25) as a solid (0.564 g, 100%) ; mp 104° C.; νmax (CDCl3) 1687 and 1769 cm-1 ; [α]D24 (c 1 in CDCl3)=-82.6; (Found: C, 69.60; H, 6.64; N, 5.35. C15H17NO3 requires C, 69.48; H, 6.61; N, 5.40%); δH (CDCl3 ; 200 MHz) 0.99 (3H, s, C(CH3)2), 1.60 (3H, s, C(CH3)2), 1.93 (3H, d, J=5.4, CH3CHCH), 5.13 (1H, s, CHPh), 7.02-7.40 (7H, m, ArCH and CH3 CH=CH); δC (125 MHz; CDCl3) 18.39 (CH3), 23.60 (CH3), 28.81 (CH3), 67.09 (CH), 82.87 (C), 122.14 (CH), 126.08 (CH), 126.19 (CH), 128.71 (CH), 129.08 (CH), 136.61 (C), 147.31 (CH), 153.50 (CO), 165.07 (CO); m/z (CI+, NH3) 260 (M+ +1).
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