Dicyclohexylcarbodiimide → t-Butyl 3-Ethyl-7beta-phenylthioacetamidoceph-3-em-4-carboxylate

Participants

Reaction Steps

A solution of N,N'-dicyclohexylcarbodiimide (620 mg, 3 mmole) in dry methylene chloride (15 ml.) was added to a stirred solution of t-butyl 7β-amino-3-ethylceph-3-em-4-carboxylate (853 mg. 3 mmole) in dry methylene chloride (10 ml.). A solution of phenylthioacetic acid (505 mg. 3 mmole) in dry methylene chloride (10 ml.) was added over 5 minutes to the mixture which was stirred at ca. 20° for 2 hours. A further portion of carbodiimide (124 mg., 0.6 mmole) was added, and the mixture was stirred for a further 30 minutes and filtered from precipitated N,N'-dicyclohexylurea. The filtrate was washed successively with 3% aqueous sodium hydrogen carbonate solution (50 ml.), water (50 ml.), 2N-hydrochloric acid (25 ml.) and water (25 ml.), dried (MgSO4) and evaporated to a yellow oil which was dissolved in ethyl acetate (8 ml.). The solution was cooled, the precipitated dicyclohexylurea was removed by filtration, and the filtrate was evaporated to give the title ester as a pale yellow foam (1.45 g.), [α]D23 + 67° (c 1.05; CHCl3), λmax. (EtOH) 250.5 nm (E1 cm.1% 256), contaminated with ca. 15% by weight of N,N'-dicyclohexylurea and/or the corresponding N-acylurea. The infra red (CHBr3) and p.m.r. (CDCl3) spectra of the product were in accord with the assigned structure.

Provenance & Evidence