Magnesium organomagnesium species

The enantioselective addition of organomagnesium compounds to ketones can be most conveniently performed by using a chiral auxiliary in the substrate molecule. Primary aUsyhnagnesium reagents react with aryl and heteroaryl ketones in the presence of magnesium TADDOLate at — 100°C, yielding products with up to 98% ee (equation 143). Chiral a-ketoacetals 214, prepared in two steps from a-substituted cinnamic aldehydes, add organomagnesium species with up to 98% diastereoselectivity (equation 144). 

The most important determination is normally the concentration of carbon-magnesium-bonded species in solution. For routine estimation of this concentration for freshly prepared solutions of organomagnesium compounds, an aliquot of the test solution may be added to an excess of standard acid, and then back-titrated with sodium hydroxide. However, this simple determination of total base will give a high estimate of organomagnesium content if products of hydrolysis or oxidation are present. Analytical methods based on the determination of the hydrocarbon formed on hydrolysis of the organomagnesium compound... 

The interpretation of such rate measurements repeatedly encountered difficulties related to the structure of the organomagnesium species present in the solutions, in particular, when solvents, such as tertiary amines or when magnesium bromide, were added [86]. 

A rather detailed scheme was presented of complexes formed between products and organomagnesium species as well as magnesium bromide. 

A range of polyfunctional organomagnesium species are available via an iodine- or a bromine-magnesium exchange reaction [75]. Since the carbon-magnesium bond is less polar than a carbon-lithium bond, considerably more func-... 

We briefly discussed in an earlier volume the behavior of the isomeric and homologous organomagnesium bromides compared to the organolithium compounds as a means of furthering our understanding of the thermochemistry of the latter species . Here, we will discuss only the magnesium compounds. Discussion of the cycloalkylmagnesium bromides is deferred to a later section in this chapter. 

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