Dimethylformamide → 7-(1-Hydroxy-1-p-bromophenacyloxycarbonylmethyl)-8-oxo-7-azabicyclo[4,2,0]oct-3-ene

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The azetidinone (28) (0.4 g) in anhydrous dimethylformamide (2 ml) was stirred with glyoxylic acid hydrate (0.32 g) in the presence of hexamethylphosphorictriamide (0.1 ml) and molecular sieves (3A; 4 pieces) for 5h. Potassium carbonate (0.226 g) was added, and the solution stirred until effervescence had ceased (5 min). p-Bromophenacylbromide (1.00 g; 1.05 equiv.) in dimethylformamide (1.0 ml) and hexamethylphosphorictriamide (0.25 ml) was added, and the solution stirred overnight. The solution was diluted with ethyl acetate, washed with saturated aqueous sodium chloride solution (×3), dried (Na2SO4) and evaporated to give a gum (1.9 g) which was chromatographed on Kieselgel. Elution of the column with ethyl acetate--petroleum ether (1:1) gave the glyoxylate ester (30). Isomer I as a foam, which slowly crystallised (ethyl acetate--petroleum ether) as needles (0.60 g) (47%) m.p. 135°-136°, νmax (CHCl3) 3250 br, 1760 sh, 1750, 1710, 1590, 970 cm-1 ; δ(d6DMSO) 1.9-2.8 (4H, m), 3.35 (1H, m), 4.17 (1H, m) 5.51 (1H, d, J 6.5 Hz; sharpens to a singlet on D2O exchange) 5.55 (2H, s, phenacyl CH2), 5.72 br (2H, s), 6.81 (1H, d, J 6.5H, D2O exchangeable), 7.75 (2H, d, J 9 Hz) and 7.90 (2H, d, J 9 Hz) (Found: C, 51.9; H, 4.2; N, 3.6; Br, 20.00. C17H16BrNO5 requires C, 51.8; H, 4.1; N, 3.6; Br, 20.3%).

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