Ketenimines carboxylic acid amide

Ketenimines from carboxylic acid amides CHCONH C C N ... 

Ketenimines are usually prepared from carboxylic acid derivatives such as amides and imino chlorides via elimination and from nitriles via alkylation with alkyl halides under strong basic conditions (21,64). 

The reactivity of ketenimines such as 146 is related to substituent R. Ketenimines were isolable when R was phenyl or alkyl. In contrast, ketenimines wherein R was halogen, thienyl, phenylthio, methylthio, or methylsulfonyl were sufficiently reactive to afford iminoethers (147) at -78°C in the presence of excess lithium methoxide. The trimethyl-chlorosilane-quinoline procedure satisfactorily converted all these substituted iminoethers to amides in good yields. The overall sequence proved amenable for use with cephalosporin acids, by prior protection of the carboxyl group as a silyl ester. Extension of this method to the penicillin series permitted the preparation of 6a-methoxyketenimine 149 and 6a-methoxyimino ether 150 from the corresponding methyl 6p-(2-chlorophenyl)acetamido and fi -dichloroacetamidopenicillanates, respectively. No further transformations of these substances were reported. 

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