Magnesium, bis

Auf analoge Weise erhalt man aus 5a-Acetoxy-6-oxo-5a-cholestan 50% d.Th. 6-Oxo-5a-cholestan. Bei der Reduktion von Allyl-athern mit Magnesium-bis-fdiathyl-cu-prat] erhalt man im wesentlichen unter C-O-Spaltung das entsprechende Aiken3. Die Reduktion verlauft i.a. ohne wesentliche Allyl-Umlagerung ab. 

Ketoesters from Imidazolides and Magnesium Bis(alkyl malonates) or Bis(alkyl thiomalonates)... 

Crowded imidazolides do not react with magnesium bis (methyl malonate) because of steric hindrance. 551... 

Figure 2 The structure of the magnesium bis(phosphoranimine) CH(Ph2PNSiMe3)2Mgl(THF) 2, with a long Mg- -C interaction. 

The magnesium bis(amide) Mg(TMP)2 (TMP = 2,2,6,6-tetramethylpiperidide) has been shown to be a useful base in the selective deprotonation of arenes to produce aryhnagne-sium amide intermediates . For example, reaction of Mg(TMP)2 with methyl benzoate... 

The concept of chiral magnesium amides for the preparation of magnesium enolates has been extended to chiral magnesium bis(sulfonamide) complexes as catalysts for the enolization of A-acyloxazolidines ° (equation 63). 

The enantioselective amination of iV-acyl oxazolidinones has been studied as part of a general approach to the synthesis of arylglycines. In this case, the enolization is initiated by a chiral magnesium bis(sulfonamide) complex. The oxazolidinone imide enolates are generated using catalytic conditions (10 mol% of magnesium complex) and treated in situ with BocN=NBoc to provide the corresponding hydrazide. 20 mol% of iV-methyl-p-toluensulfonamide are added to accelerate the reaction (equation 117). 

Magnesium bis(hexamethyldisilazide), Mg(HMDS)2, catalyses the enolization of ketones.287 On addition to propiophenone in toluene at ambient temperature, a ca 3 1 E Z mixture of enolates (103, R=SiMe3) is formed. These enolates, and an initial ketone complex, have been characterized by NMR, X-ray, IR, and UV-visible spectroscopy and computational studies. Kinetics of tautomerization have been measured, with proton transfer confirmed as rate determining ( hAd = 18.9 at 295 K). The significant temperature dependence of the primary isotope effect is indicative of tunnelling. 

Mercaptobenzophenone reacts with ajl-unsaturated esters and nitriles in the presence of magnesium bis(diiso-propyUamide (MBDA) to yield 4-hydroxythiochroman-3-carboxylic acid derivatives. Dehydration to the thiochro-mene is facile (Scheme 169) <1999J(P1)1547>. 

A catalytic approach to the synthesis of arylglycines was proposed by Evans and coworkers using enantioselective amination of iV-acy 1 oxazolidinones [54], Metallo-bis(sulfonamide) complexes derived from chiral diamines are potential chiral catalysts. The magnesium-bis(sulfonamide) complex 109 was generated by treating (S,S)-bis(sulfonamide) 108 with dimethylmagnesium in dichloromethane (Scheme 50). 

The chemistry of magnesium bis-amides has been reviewed.21 Magnesium bis-amides have been used for the region- and stereoselective formation of enolates.2 a Enantioselective enolization with chiral magnesium amides has been applied in asymmetric synthesis.23 233... 

Due to ab initio SCF calculations the favored bicyclic structure of the alkaline earth metal bis(phosphanides) can be explained by small, but structure dominating d orbital participation. Whereas the monocyclic magnesium bis(phosphanide) H2P-Mg(p-PH2)2Mg-PH2 with a C2/, symmetry is favored by 27.9 kJ/mol against the bicyclic Ci symmetric bicycle, the bicyclic compounds M(p-PH2)3M-PH2 of calcium and strontium are lower in energy [5]. In the case of the... 

Mg bisamides can also be used as strong and selective bases in the formation of synthetically useful enolates. Less higlily substituted silyl enol ethers are regiospecifically prepared in high yield, at approximately room temperature under kinetic conditions, from unsymmetrical cyclic ketones and magnesium bis(diiso-propylamide)[(DA)2Mg] in THF/heptane (Scheme 3.36) [27]. 

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