Magnesium catalyzed

The body s normal daily magnesium requirement is 300 to 350 mg/day to maintain a serum magnesium concentration of 1.5 to 2.4 mg/dL (0.75 to 1.2 mmol/L). Because magnesium is the second most abundant ICF cation, serum concentrations are a relatively poor measure of total body stores. Magnesium catalyzes and/or activates more than 300 enzymes, provides neuromuscular stability, and is involved in myocardial contraction. Magnesium is generally not part of standard chemistry panels, and therefore must be ordered separately.2,37,42 44,45... 

G. Barkhordarian, T. Klassen, R. Bormann, Kinetic investigation of the effect of milling time on the hydrogen sorption reaction of magnesium catalyzed with different Nb205 contents, J. Alloys Compd. 407 (2006) 249-255. 

N. Hanada, T. Ichikawa, S. Hino, H. Eujii, Remarkable improvement of hydrogen sorption kinetics in magnesium catalyzed with Nb Oj, J. Alloys Compd. 420 (2006) 46 9. 

Finally, for MPV reduction we find nearly equal barriers for aluminium and gallium, and a much lower one for magnesium. Again, one should be careful not to attach too much value to these numbers, since for magnesium-catalyzed MPV, in particular, the metal will probably prefer a higher coordination number than 4. 

FIGURE 1 7.4 Proposed transition states for the copper- and magnesium-catalyzed asymmetric Diels-Alder reaction. 

Severin reported that 0.05-5 mol% of 152 in the presence of magnesium catalyzed 5-exo cyclizations and even the significantly slower 5-endo and 9-endo cyclizations of dichloroacetamides, a-bromoamides, or trichloroacetates in 66-94% yield [220],... 

Chiral acylthiazolidinethiones such as 26 can readily be prepared from commercially available amino acids in three steps12 (Scheme 2.2k). They have been employed as a synthetically useful auxiliary in diastereoselective aldol reactions.13 The magnesium-catalyzed aldol reaction of the thiazolidinethione 26.S with cin-namaldehyde afforded 27 as a major diastereomer in 87% yield. Interestingly, compound 27 is the opposite anti-aldol diastereomer to that seen with the oxa-zolidinone 23S. 

The Oppenauer oxidation can also afford a convenient alternative to more traditionally used oxidants. Oxidation of quinine (13) using benzophenone and KO/Bu gave the ketone in excellent yield (Figure 3.14) other oxidants were less effective [27]. This reaction can be viewed as an Oppenauer oxidation or a Meerwein-Pondorf-Verley reduction, depending on whether one considers the oxidation or the reduction to be the primary reaction. A magnesium-catalyzed Meerwein-Pondorf-Verley reduction was determined to form significant amounts of impurities in a Grignard reaction [28]. 

Alkaline Earth Metals. In the early literature, similar to alkali earth metals, alkaline earth metals were usually used to form the enolates, especially magnesium enolates, in the aldol reaction (128,129). Inspired by heterogeneous MgO solid base catalysis (130), alkaline earth metals have been applied successfully as homogeneous catalysts in the aldol reaction (Scheme 23). In 1998, Corey and co-workers described a new magnesium-catalyzed diastereoselective anti-aldol reaction as a key step for the total synthesis of lactacystin (131). The metal requirement is strict, since several salts were tested, for example, TiCl4, SnCL, ZnCl2, and Cu(OTf)2, only Mgl2 functioned as an effective catalyst (Scheme 24). 

Yamamoto et al prepared polythiophene by the dehalogenative coupling of 2,5-dibromothiophene with magnesium catalyzed by nickel(II) chloride and bipyridine [86]. Lin and Dudek also prepared polythiophene in a similar way [87]. The conductivity of a polythiophene pellet was 10 "Scm and was enhanced to 0.1 S cm after doping with iodine. 

Scheme 18 Magnesium-catalyzed hydroboiation/dearomatization of pyridines, quinoline and...

Scheme 19 Magnesium-catalyzed hydroboiation of aldehydes and ketones...

Fig. 13 (a) Simplified mechanism for the magnesium-catalyzed hydroboration of carbonyls (b) Borate formation during group 2-mediated hydroboration chemistry... 

Scheme 25 Magnesium-catalyzed amine-boiane dehydrocoupling...

Reaction mechanism Kinetic analysis of the magnesium-catalyzed reaction in combination with stoichiometric studies has elucidated a mechanism which proceeds via (1) catalyst initiation to form a magnesium amide catalyst, (2) turnover-limiting nucleophilic attack of the amide nitrogen on the silane to form an... 

Scheme 26 (a) Calcium- and (b) magnesium-catalyzed amine-silane dehydrocoupling... 

Fig. 17 Proposed mechanism of the magnesium-catalyzed dehydrocoupling of amines and silanes...

Yamamoto et al, [24] have studied the polymerization of 2.5-dibromothiophene by debromination with magnesium, catalyzed by nickel compounds ... 

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