Bromomagnesium enolates

The methods previously used to obtain single aldol products (or their dehydrated derivatives) from reactants where several aldol products are possible8 include the reaction of bromozinc enolates, from a-bromo-ketones, with aldehydes 9 the reaction of bromomagnesium enolates, from either a-bromoketones or from ketones and bromomagnesium... 

The action of magnesium on a-halo ketone has been used by Malmgren, for the synthesis of bromomagnesium enolate 2 derived from 3-bromocamphor 1 (equation 1) . 

Felhnann and Dubois have described the structure of the enolate 29 derived from the reaction of f-butyl acetate with (MeO)2Mg. The NMR spectrum reveals two O-metallated species, which should be symmetric enolates as proposed by Pinkus and Wu for the bromomagnesium enolate of methyhnesityl ketone (metal is tricoordinated). ... 

The bromomagnesium enolate n-BuC(=CH2)OMgBr HMPA is an oxygen bridged dimer ° while -PrC(=CMe2)OMgBr HMPA is monomeric, probably due to steric hindrance. A study of the monomer/dimer equilibrium for ROMgBr HMPA (R = Me, Et, -Pr, f-Bu, Vi, isopropenyl etc.) would be desirable. 

The free monomeric hydroxy aldehydes are difficult to obtain by hydrolysis of the oximes. Bromomagnesium enolates prepared from Grignard reagents and sterically hindered ketones act as true Grignard reagents. /3-keto alcohols are formed by their reaction with aldehydes or ketones. ... 

In some cases, however, there is a significant bias in favor of the more stable aldolate. For example, the kinetic product mixture in the reaction of the bromomagnesium enolate of ethyl r-butyl ketone and... 

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