Magnesium reagent

Lithium ethoxyacetylide appears superior to the magnesium reagent for avoiding further transformations of particularly sensitive alcohols produced in this reaction. 

By application of the most common procedure—i.e by using an a-silylated organolithium or magnesium reagent—the /3-hydroxysilane 5a/5b can be isolated. However in the case of M = Na or K, the alkoxide oxygen in 4a/4b is of strong ionic character, and a spontaneous elimination step follows to yield directly the alkene 3. 

Recently, attempts were made to replace the air- and moisture-sensitive zinc and magnesium reagents in the copper-catalysed asymmetric conjugate addition, with... 

Zincate reagents can add to imines with or without Lewis acid catalysis. Alkylimines require BF3 but imines of pyridine-2-carboxaldehyde react directly. If the imines are derived from chiral amines, diastereoselectivity is observed. Both a-phenylethyl amine and ethyl valinate have been tried. Higher enantioselectivity was observed with mixed magnesium reagents.175... 

Acetoxy-1,3-alkadienes give mainly e-alkylation with dialkylcopper-magnesium reagents. 

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. 

Most gratifyingly, these conditions are also applicable to functionalized magnesium reagents [33], as demonstrated by the formation of a-hydroxyallenes 31-34 from ds- or trans-27 and the corresponding magnesium cuprates bearing substituted aryl groups (Scheme 2.11) [31]. 

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... 

TABLE 4. Carbonyl carbon-14 KlEs, substituent effects and enone isomerization for the reactions of organolithium and magnesium reagents with benzophenone"... 

By analogy with oxazoles and N-substituted imidazoles, thiazoles and benzothiazoles unsubstituted at C-2 undergo direct metalation at that position, with sodium, lithium, or magnesium reagents (Scheme 91)[79MI1 ... 

In those cases where the initially added electrophile is chemically nonreactive toward the magnesium reagent, further reaction can be achieved to give a 6-magnesium species 334, and this can be performed either separately, or in a one-pot procedure <2006OL3737>. 

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