Lithium magnesiate

Bach has used the selective exchange reaction on 2,4-dibromothiazole for the synthesis of substituted 4-bromothia-zoles.59,59a Lithium magnesiates, prepared by the reaction of an organolithium reagent (2 equiv.) and an... 

In this section, the surprisingly diverse structural chemistry of recently published lithium magnesiate complexes, containing carbon- and/or nitrogen-based anions, will be surveyed. Since 2007, several different structural motifs have been reported. In this section, these will be summarized according to the ligand sets within the lithium magnesiate framework. 

The monomeric tris(carbanion) motif is the simplest structural form of a lithium aU-carbanionic magnesiate. To isolate this particular form, the use of a multidentate Lewis basic donor compound is generally required. Hevia and coworkers have reported the PMDETA N N N",N" N -pentamethyldiethylenetriamine) solvated monomeric lithium magnesiate... 

Three solvent-separated tris (amido) lithium magnesiates have been reported since 2007. All three are tris(HMDS) (1,1,1,3,3,3-hexamethyldisiliazide)... 

Two halide containing amido lithium magnesiates [(THF)3LiMg(TMP) Cy 18 (Fig. 13) and the dimeric [(THF)2LiMg(N Pr2)Cl2]2 19 (Fig. 14) have recently been reported. These are of particular importance to the well-developed synthetic area of turbo-Hauser metalation chemistry pioneered... 

Another lithium magnesiate arises hum the double magnesiation of Af-methyl-l,3-propylenediaminoboryl ferrocene (Fc -H2). The trimagnesium-bridged ferrocenophane [(THP)2Li2Mg3(TMP)2(Fc )2] 26 (Fig. 19, where THP is tetrahydropyran) has a motif which has been previously observed. ... 

Fig. 20 Generic Weiss-motifs of lower order (left) and higher order (right) lithium magnesiates (R = alkyl anion, LD = neutral Lewis Donor)...

The utility of these trisalkyl lithium magnesiates for metal-halogen exchange has also been exploited for the functionalisation of copolymerised bromopolyst5rene beads [66]. 

Lithium magnesiate LiMgBus has been used for the smooth magnesium/bromine exchange of 5-bromo-2-methoxypyridine as an entry to the biologically active 5-substituted-2-methoxypyridines at 0 °C in THF, obtaining the desired electrophilically quenched products in reasonable yield [67]. This protocol displayed... 

Fig. 24 Contrasting reactivity of butyl vs. methyl lithium magnesiates in metallation reactions of dibromomethylsilanes...

Fig. 26 Allylation reactions using a lithium magnesiate reagent...

Sosnicki and Struk were also able to apply their allyl/alkyl lithium magnesiate base in a one-step symmetrical double alkylation of lactams at the challenging carbon site adjacent to the carbonyl group [78]. The dual alkylation was assigned to the reactivity of Bu2Mg which was believed to be extruded after the first alkylation but is basic enough to execute a second magnesiation (Fig. 26b). 

Magnesiation. Lithium magnesiates have proven to be effective in the deprotonation of the 2-position of oxazole to furnish the 2-Mg adduct. Similar to the lithiated species, the resulting met-alated compound exists in equilibrium between the ring-closed heterocycle and the ring-opened isonitrile. However, the former proved to be more reactive and amenable to Kumada-type coupling (eq 19). ... 

Fig. 8 Common Weiss motifs - lower-order (top left) [36], higher-order (top right) [37] and solvent-separated higher-order (bottom) [38] lithium magnesiate complexes...

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