Dimethylformamide → 4-Methoxybenzyl 2-[(3S,4S)-4-t-Butyldimethylsilyloxymethyl-2-oxo-3-tritylaminoazetidin-1-yl]acetate

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(3S,4S)-4-t-Butyldimethylsilyloxymethyl-3-tritylaminoazetidinone (IV), (1.67 g) [H. Mastalerz et al., J. Med. Chem., 1988, 31, 1190] as a suspension in acetonitrile (40 ml) was treated with DMF (20 ml) to obtain a clear solution. Cesium carbonate (1.29 g) followed by 4-methoxybenzyl bromoacetate (1.19 g) were added and the mixture vigorously stirred overnight. T.l.c. analysis showed no starting material, the solution was diluted with ethyl acetate and washed with water (4×), brine and then dried. Removal of solvent in vacuo and purification by flash chromatography afforded the title compound as a pale yellow foam, (1.744 g, 76%), νmax (CH2Cl2) 1760 and 1744 cm-1 ; δH (CDCl3) -0.06 and -0.13 (6H, 2s), 0.81 (9H, s), 1.60 (1H, brs), 2.44 (1H, dd, J 3.3, 11.7 Hz), 3.1 (1H, dd, 2.2, 11.7Hz), 3.29 (1H, m), 3.41 (1H, d, J 18.0 Hz), 3.80 (3H, s), 4.36 (1H, d, J 18.0 Hz), 4.45 (1H, m), 4.97 and 5.05 (2H, ABq, J 11.8 Hz), 6.85 (2H, d, J 8.7 Hz), 7.16-7.30 (15H, m) and 7.52 (2H, d, J 8.7 Hz); [mass spectrum: MH+ (651)].

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