Phosphorus pentachloride → benzhydryl (6R)-3-(chloromethyl)-7-[[(2Z)-2-methoxyimino-2-[2-(tritylamino)-1,3-thiazol-4-yl]acetyl]amino]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate

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Benzhydryl 7-amino-3-chloromethyl-3-cephem-4-carboxylate prepared in Preparation No. 4 (2.29 g, 5.52 mmoles) in CH3CN (57 mL) was treated with bis(trimethylsilyl)acetamide (BSA, 4.09 mL, 16.6 mmoles) at room temperature for 50 minutes to give a clear solution. To the solution was added an acid chloride solution, which was prepared from (Z)-2-methoxyimino-2-(2-tritylaminothiazol-4-yl)acetic acid (IVa) (2.04 g, 4.60 mmoles) and PCl5 (1.15 g, 5.52 mmoles) in methylene chloride (20 mL). The mixture was stirred at room temperature for 30 minutes, poured into cold water (200 mL) and extracted with ethyl acetate (3×100 mL). The combined extracts were washed with aqueous NaCl, dried and evaporated. The residual syrup (4 g) was chromatographed on a silica gel (150 g) column by eluting with 10:1 and 3:1 mixtures of toluene and ethyl acetate successively. The fractions containing the desired compound were combined and evaporated to afford 2.61 g (68%) of VIa as an amorphous powder.

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