[CH3:1][S:2][CH:3]1[NH:6][C:5](=[O:7])[CH2:4]1.[H-].[Na+].[H][H].Br[CH2:13][C:14]#[C:15][C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][C:17]=1[C:22]([O:24][CH2:25][C:26]1[CH:31]=[CH:30][C:29]([O:32][CH3:33])=[CH:28][CH:27]=1)=[O:23].[Br-]>CN(C)C=O>[CH3:1][S:2][CH:3]1[N:6]([CH2:13][C:14]#[C:15][C:16]2[CH:21]=[CH:20][CH:19]=[CH:18][C:17]=2[C:22]([O:24][CH2:25][C:26]2[CH:31]=[CH:30][C:29]([O:32][CH3:33])=[CH:28][CH:27]=2)=[O:23])[C:5](=[O:7])[CH2:4]14-Methylthioazetidin-2-one (470 mg., 4 mmole) was dissolved in dry dimethylformamide (10 ml.) and the solution was stirred at -20° with exclusion of moisture while sodium hydride (50% dispersion in oil, 200 mg., 4 mmole) was added. When evolution of hydrogen had ceased (ca 10 minutes), 3-bromo-1-[o-(p-methoxybenzyloxycarbonyl)-phenyl]-prop-1-yne (1.44 g., 4 mmole) in dry dimethylformamide (5 ml.) was added dropwise to the stirred mixture at -20°. After addition of the bromide was complete, the mixture was warmed to 0° and stirred at that temperature for 30 minutes. The mixture was poured into ice-water (50 ml.) and the aqueous mixture was extracted twice with ethyl acetate (50 ml. portions). The combined ethyl acetate extracts were washed three times with water (30 ml. portions). The solution was dried (magnesium sulphate) and the solvent was evaporated under reduced pressure to yield a yellow gum. The gum was chromatographed on silica gel (25 g.) using ethyl acetate/petroleum ether (b.p. 60°-80°) to give the title compound as a colourless gum (400 mg., 26% yield). (Found: M+, 395.11850. C22H21NO4S requires 395.11912). νmax (CHCl3): 1760 (β-lactam C=O), 1730 (ester C=O), 1620 and 1520 (aromatic C=C) cm-1. δ (CDCl3): 2.10 (s, 3H, SCH3), 2.91 (dd, J 15, J' 3 Hz, 1H, β-lactam CHH), 3.35 (dd, J 15, J' 6 Hz, 1H, β-lactam CHH), 3.75 (s, 3H, OCH3), 3.86 (d, J 16.5 Hz, 1H, NCHH), 4.42 (d, J 16.5 Hz, 1H, NCHH), 4.94 (dd, J 6, J' 3 Hz, 1H, β-lactam CH), 5.35 (s, 2H, OCH2Ar), 6.95 (d, J 8.5 Hz, 2H, Ar-H), 7.2-7.6 (m, 5H, Ar-H), 7.95 (m, 1H, Ar-H). m/e: 395 (M+, 1%), 348 (14), 274 (63), 205 (37), 168 (56), 159 (68), 158 (44), 122 (76), 121 (100).
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