Magnesium hexamethyldisilazide

Enolsilylation Magnesium hexamethyldisilazide, which is prepared electro-chemically with a Mg anode, deprotonates ketones. An ensuing silylation delivers the silyl enol ethers. 

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. 

Deprotonation of 14 can also be achieved by reaction with lithium hexamethyldisilazide. Following deprotonation of the amino group the 13C NMR spectrum exhibits a resonance at 182.3 ppm for the C2 carbon, suggesting a stronger interaction of the carbene with the magnesium centre. 

ALLYLIC ALCOHOLS Alkyllithium reagents. Bis(triphenylphosphine)-copper(I) tetrahydroborate. r-Butyl-dlmethyliodosilane. Chlorotrimethyl-silane. Cyclohexylisopropylamino-magnesium chloride. Iodotrimethyl-silane. Lithium aluminum hydride-N-Methylephedrine. Lithium 1 -[Pg.240]

Several variations have been shown to improve the efficiency microwave irradiation makes the process very rapid " and the use of iodine on a clay support " are just two of these. An alternative to the use of ammoifia for the synthesis of A-unsubstituted-pyrroles employs hexamethyldisilazide with alumina, " or a solution of ammonia can be generated in situ conveniently, using the reaction of magnesium nitride, MgsNa, with methanol. " ... 

Bromomagnesium hexamethyldisilazide and bromomagnesium diisopropylamide were the most effective of several magnesium bases examined for selective formation of the more substituted silyl enol ether fromketones (eq 1). Less-hindered ketones gave mainly aldol products. ... 

The redox-neutral dimerization of aldehydes to form esters known as the Tischenko (or Tischtschenko) reaction may be catalyzed by group 2 hexamethyldisilazides [M N(SiMe3)2 2(THF)2] (M = Ca, Sr, and Ba), bio-inspired magnesium thiolate complexes or with bicyclic guanidinate-stabilized magnesium amide complexes (Scheme 23) [139-142]. 

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