Triethylamine (263 mg, 2.6 mmol) is added by syringe to a mixture of (3S,4R)-3-[(R)-1-hydroxyethyl]-4-[3-(4-nitrobenzyl)oxycarbonyl-2-oxopropyl]azetidin-2-one, (253 mg, 0.72 mmol) and p-carboxybenzene sulfonylazide (196 mg, 0.84 mmol) in dry acetonitrile (6 ml) at 0° C. When addition is complete the cooling bath is removed and the reaction mixture is stirred at room temperature for 1 hour. The mixture is then diluted with ethyl acetate (50 ml) and filtered. The filtrate is concentrated in vacuo and the residue is chromatographed on a short silica gel column (ethyl acetate) to yield 222 mg, (81% overall from (3S,4R)-1-(t-butyldimethylsilyl)-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-4-[3-(4-nitrobenzyl)oxycarbonyl-2-oxopropyl]azetidin-2-one) of (3S,4R)-3-(R)-1-hydroxyethyl)-4-[3-(4-nitrobenzyl)oxycarbonyl-2-oxo-3-diazopropyl]azetidin-2-one as a white solid m.p. (dec.) 163° C. IR(CHCl3, CM-1) 3410, 2132, 1756, 1718, 1650, 1350, 1280, 1120; n.m.r. (CDCl3) δ7.9 (2d-aromatic,4), δ5.4 (s,2), δ6.2 (brs,1), δ4.1 (m,2), δ2.6-3.6 (m,4), δ1.32 (d,3,J=6.2).
