Pivaloyloxymethyl bromide (0.10 g, ca. 0.5 mmol) and sodium iodide (0.1 g) in acetone (1 ml) were stirred for 0.25 h, filtered and evaporated in vacuo. The iodide in toluene (0.5 ml) was added to sodium (6R,7R)-7-[2(2-aminothiazol-4-yl)-2-(Z)-methoxyiminoacetamido]-3-[(5RS)-2-oxotetrahydrofuran-5-yl]ceph-3-em-4-carboxylate (0.124 g, 0.25 mmol) in N-methylpyrrolidone (2 ml) and stirred for 0.5 h. The reaction mixture was diluted with ethyl acetate, washed twice with water, and with brine, dried, concentrated and flash chromatographed on silica gel eluting with 80,90,100% ethyl acetate in hexane to give the title compound (86 mg, 59%), νmax (CH2Cl2) 1780, 1753, 1735, 1682, 1532, 1374, 1121, 1046 cm-1 ; δH (250 MHz, CDCl3) (9H, s), 1.9-2.2 (1H, m), 2.4-2.8 (3H, m), 3.34 and 3.64, 3.48 and 3.59 (together 2H, 2ABq, J 18.9, 18.4 Hz), 4.08 (3H, s), 5.10, 5.11 (together 1H, 2d, J 4.9 Hz), 5.35 (2H, bs), 5.5-5.95 (3H, m), 6.00, 6.10 (together 1H, 2dd, J 9, 4.9 Hz), 6.85, 6.87 (together 1H, 2s), 7.52, 7.54 (together 1H, 2d, J 9 Hz); [mass spectrum: +ve ion (3-nitrobenzyl alcohol-sodium acetate) MH+(582) MNa+(604)].
