Bromotrimethylsilane (0.31 g) in dichloromethane (3 ml) was added to a cooled (0°) stirred mixture of (R and S)-1-acetoxyethyl (6R,7R)-3-dimethoxyphosphorylcarbamoyloxymethyl-7-[Z-2-(fur-2-yl)-2-methoxyiminoacetamido]ceph-3-em-4-carboxylate (0.62 g) and trimethylsilylurethane (0.16 g) in dry dichloromethane (12 ml) in a nitrogen atmosphere. After 2.5 hours the reaction mixture was evaporated in vacuo to a foam. This foam was dissolved in ethyl acetate (30 ml) although a slight precipitate remained. The filtered organic solution was treated with saturated aqueous sodium bicarbonate solution (30 ml) and the aqueous solution was layered with butan-1-ol (20 ml) and acidified to pH 0.5 by addition of concentrated hydrochloric acid. The aqueous phase was extracted with butan-1-ol (2×15 ml) and the combined organic extracts were evaporated in vacuo to give a solid. Trituration of this solid with di-isopropyl ether afforded the title ester (0.396 g) as a solid; νmax (Nujol) 3270 (NH), 1788 (β-lactam), 1734 (CO2R) and 1684 and 1540 cm-1 (CONH); τ (DMSO-d6) 0.18 (d, J 8 Hz, NH), 2.9 to 3.4 (broad m, 2 superimposed q, CHCH3), 4.14 (m, 7-H, mixture of diastereoisomers), 4.76 (m, 6-H, mixture of diastereoisomers), 7.92 (s, OCOCH3) and 8.52 (d, J 5 Hz, CHCH3).
