Magnesium amides hindered

In recent years, a variety of hindered magnesium amides have been used to produce magnesium enolates. The versatility of these bases is now well recognized. Some typical examples are presented below. 

The magnesium amides of choice for the preparation of magnesium enolates via met-allation are the Hauser bases, such as 39 and 40, or (bis)amidomagnesium reagents, such as 46 and 47. The reaction has been successfully applied to the preparation of enolates derived from cyclic, acyclic and a-siloxyketones, benzyUc ketones, aldehydes, carboxylic esters and amides, even with the less hindered Hauser bases. 

Reaction of aLkyknagnesium reagents with sterically hindered amines leads to the formation of magnesium amides 110-112 °, reacting much faster than the parent alkyl-magnesium derivatives with C—H acidic substrates (Scheme 9). 

Bromomagnesio-3,5-dicyanocubane-2-(N,N-diisopropyl)carboxamide (metallation by sterically hindered magnesium amide) [12]... 

The reactions of alkylmagnesium reagents with sterically hindered amines in THF lead to the formation of magnesium amides 56-58,which react with C-H acidic substrates much faster than alkylmagnesium reagents (Scheme 2-25). 

These reagents are appropriate even for very sensitive molecules. Their efficacy is presumably due to the Lewis acid effect of the aluminum and magnesium ions. The hindered nature of the amide bases also minimizes competition from nucleophilic ring opening. 

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