Preparation magnesium reagents

Preparations. Magnesium alkyls maybe prepared from a Grignard reagent according to the following disproportionation reaction ... 

Preparation of allyltitaniums of the type (allyl)Ti(OiPr) 3 from the corresponding allyl-lithium or -magnesium compounds and ClTi(OiPr)3 by transmetallation and their subsequent synthetic utilization have attracted considerable interest because of the advantageous reactivity of the allyltitaniums as compared to other allylmetal complexes in terms of chemo-, regio-, and diastereoselectivity [3], The preparation of certain allyllithium or -magnesium reagents, however, is not necessarily easy, which would seem to limit the utility of this method. 

G. Cahiez, S. Marquais, and M. Alami 135 MANGANESE-COPPER-CATALYZED CONJUGATE ADDITION OF ORGANO-MAGNESIUM REAGENTS TO a,(J-ETHYLENIC KETONES PREPARATION OF 2-(1,1 -DIMETHYL-PENTYL)-5-METHYLCYCLO-HEXANONE FROM PULEGONE... 

Chiral organomagnesium amides form an efficient method to realize enantioselective conjugate addition. Sibi and Asano have reported the Michael addition of cr-bound magnesium reagents derived from bisoxazolines to enamidomalonates (equation 41). The enantioselectivity of the addition is discussed in Section El. This method allows the preparation of chiral -amino acid derivatives. ... 

Nnmerons other protocols have been developed to prepare magnesium enolates by asymmetric 1,4-addition of Grignard reagents to electron-deficient alkenes. Recently, an enantioselective metal-catalyzed version of this key reaction has been studied with enones and a, S-unsaturated thioesters Using chiral ferrocenyl-based diphosphines leads to... 

Recently, the preparation of functionalized benzyUc magnesium reagents 73 could be realized by using a new sulfur-magnesium exchange reaction (equation 47). I/Mg... 

The mechanisms are complex, particularly in the organomagnesium (Grignard) reactions. Several reactive species are present, and the product metal alkoxide can complex with unreacted organometallic. Furthermore, trace transition metal impurities in the magnesium used to prepare Grignard reagents appear to facilitate electron transfer and may cause the reaction to proceed at least partly by a radical pathway. See (a) J. Laemmle, E. C. Ashby, and H. M. Neumann, J. Amer. Chem. Soc., 93, 5120 (1971) (b) E. C. Ashby, J. Laemmle, and H. M. Neumann, Accts. Chem. Res., 7,272 (1974). 

Prepare the reagent as follows. To a mixture of 100 ml of pure t-butyl alcohol (2-methylpropan-2-ol) and 25 ml of 30 per cent hydrogen peroxide, add anhydrous sodium sulphate or magnesium sulphate in small portions two layers separate out. Remove the alcohol layer which contains most of the hydrogen peroxide, and dry it with magnesium sulphate, followed by anhydrous calcium sulphate. The resulting liquid is a stable solution of 6.3 per cent hydrogen peroxide in t-butyl alcohol. 

Aqueous solutions for linearity and precision studies were prepared from reagent-grade salts of sodium, potassium, calcium and magnesium (Sigma, USA). 

Finally perfluorinated alkenes, prepared according to various routes (decarboxylation of perfluorinated acids or anhydrides, action of organolithium, magnesium reagents or metallic zinc-copper couple to perfluoroalkyl iodides, oligomerisation of TFE and of HFP, addition of perfluoroalkyl iodides to per-fluoroallyl chloride [304], addition of KF to perhalogenated esters or alkanes... 

Yasuda has prepared magnesium, boron, and copper reagents by trans-metallation from the lithium derivatives. All these compounds are very regioselective toward aldehydes as well as toward ketones, giving essentially only C-3 addition (104). Diphenylpentadienylborane, prepared in situ from... 

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