Bromo-oxime ether

A useful application of an enolate-oxime ether condensation, described by Weeks, Volkmann and co-woricers, is found in the synthesis of 6-aminomethylpenicillin derivative (218), a potent -lactamase inhibitor. As shown in Scheme 45, the sensitive penicillin Grignard (216) is condensed with ethyl formaldoxime at -80 C in the presence of Bp3-OEt2 to afford adduct (217). The use of Bp3-OEt2 is critical because it allows the reaction to proceed at the low temperature required for the stability of enolate (216). Hydrogenolysis of (217) simultaneously results in removal of the ethoxy, bromo and benzyl groups, affording (218). 

Trifluoro-2-nitrosopropene can be generated in situ from 1 -bromo-3,3,3-trifluoropropan-2-one 2-oxime. It is a highly reactive nitrosoalkene that readily undergoes cycloaddition with silyl enol ethers and other die-nophiles to give CF3- substituted 1,2-oxazines (92JOC339). 

The imidazole ketone (470) is produced by the action of benzylamine on the oxime Ac2C=NOH. Toluene-p-sulphonyl-alkyl isocyanides TosylCHRNC (R = Me, Et, or CHaPh) react with benzylideneaniline to form the imidazoles (471). Treatment of the bromo-ketone MeC0CHBrCH20Me with a mixture of formaldehyde, methylamine, and ammonia gives about equal amounts of the ethers (472) and (473). Trimethylsilyl enol ethers Me3SiOCH=CHR (R= H... 

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