Reactivity organomagnesium amides

The synthesis of ketones from organomagnesium compounds and N,N-dialkylamides has been comparatively little exploited, but a few examples are included in Table 6.5. A significant limitation has been the low reactivity of the amides, but this has been overcome by the use of 7V-(2-pyridyl)amides (see penultimate entry in Table 6.5) and especially A-methoxyamides (hydroxamates). Examples of the use of the latter are listed in Table 6.6. 

Chloroformates, chlorocarbamates, and phosgene are similarly reactive toward organomagnesium compounds. The first two provide useful syntheses of esters and amides, respectively, but phosgene usually leads to the tertiary alcohol. 

Amides and Lactams. The amide carbonyl group is less reactive than that of aldehydes or ketones, but the intermediate formed on addition of one equivalent of organomagnesium compound is relatively stable to elimination of a magnesium dialkylamide, and so protects... 

Addition to the C=N of an imine forms the magnesium amide, which is hydrolyzed to an amine. Isolated C=N double bonds of simple imines are relatively unreactive toward organomagnesium compounds, and may instead be depro-tonated at the a-position. Oximes and other N-substituted imines may react better, although an alternative sequence can produce aziridines. Imminium ions, because of their positive charge, are more reactive, and are useful in making tertiary amines. A-Silylimines yield primary amines after hydrolysis. Grignard reagents also add to one C=N of carbodiimides to produce amidines, and to nitrones to produce hydroxylamines. Some varied examples are shown in Scheme 6. 

---