3-Trifluoromethylcephalosporins. I. Total synthesis of tert-butyl (.+-.)-7-amino-3-trifluoromethyl-3-cephem-4-carboxylate.

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tert-Butyl (±)-7-amino-3-trifluoromethyl-3-cephem-4-carboxylate (16) and the 2-cephem derivative (21) were obtained by total synthesis starting from tert-butyl N-benzylideneglycinate (1). This synthesis is the first example of the reaction of the N-benzylideneglycinate anion with a reactive α-haloketone to give a β-hydroxy-γ-halo-α-aminoester (5a and 5b). The amino esters were treated with ethyl thioformate and then potassium carbonate, leading to the 4, 5-dihydro-6H-1, 3-thiazine derivatives (8a and 8b). After cycloaddition of 8a and 8b with azidoacetyl chloride and catalytic hydrogenation of the azido group, the resulting trans 7-aminocephem compound (12) was converted to the cis isomer (16) by the established method, involving reduction of the o-nitrobenzenesul-fenimino derivative (14).

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