To a stirred solution of diphenylmethyl 7-(2-thienylacetamido)-3-formyl-2-cephem-4-carboxylate (1.556 g) in a mixture of tetrahydrofuran (30 ml) and toluene (30 ml) is added a solution of methylmagnesium iodide (1.853 mM/ml) in ether (13 ml) during 4 minutes at -40° C. After 15 minutes, the reaction mixture containig diphenylmethyl 7-(2-thienylacetamido)-3-(1-iodomagnesium oxyethyl)-2-cephem-4-carboxylate is poured into an aqueous saturated solution of ammonium chloride (30 ml), and is extracted with acetate. The extract solution is washed with saturated saline, dried over sodium sulfate, and evaporated under reduced pressure to give diphenylmethyl 7-(2-thienylacetamido)-3-(1-hydroxyethyl)-2-cephem-4-carboxylate, IR: νmaxCHCl 3 3400, 3350, 1780, 1750, 1685, 1505 cm-1. The product is dissolved in pyridine (16 ml), and is mixed with acetyl chloride (0.47 ml) under ice cooling. After 35 minutes, the reaction mixture is decomposed with a small amount of ice, poured into water after 10 minutes, and is stirred with ethyl acetate under ice cooling. The solution is neutralized with 4N-hydrochloric acid to pH 2.5, and is extracted with ethyl acetate. The extract solution is washed with saturated saline, dried over sodium sulfate, and evaporated under reduced pressure. Purification of the residue (1.66 g) by chromatography over silica gel (68 g) gives from fractions eluted with a mixture of benzene and ethyl acetate (6:1) diphenylmethyl 7-(2-thienylacetamido)-3-(1-acetoxyethyl)-2-cephem-4-carboxylate (625 mg: a mixture of stereoisomers). Colorless amorphous powder. Yield: 36.3%. NMR: δCDCl 3 1.21d(7.3Hz)3H, 1.73s+1.83s3H, 3.80s2H, 5.0-5.6m4H, 6.38br-slH, 6.9-7.4ml4H. IR: νmaxCHCl 3 3400, 1782, 1746, 1690, 1502 cm-1.
