Enolates sodium hexamethyldisilazide

Silyl enol ethers, 23, 77, 99-117,128 Silyl enolates, 77 Silyl peroxides, 57 Silyl triflate, 94 Silyl vinyl lithium, 11 (E)-l -Silylalk-1 -enes, 8 Silylalumimum, 8 Silylation, 94 reductive, 26 a-C-Silylation, 113 O-Silylation.99,100 / -SilyIketone, 54 non-cydic, 55 Silylmagnesium, 8 Silyloxydienes, 112 Sodium hexamethyldisilazide, 89 Sodium thiosulphate pentahydrate, 59 Stannylation, see Hydrostannylation Stannylethene, 11 (Z)-Stilbene, 70 (E)-Stilbene oxide, 70 /3-Styryltrimethylsilane, 141 Swern oxidation. 84,88... 

Reaction of achiral biscyclopentadienyl zirconium-( /2-acyl-C,0) complexes, such as la and lb, with sodium hexamethyldisilazide generates the di-hapto enolates 2a and 2b91. Enolate 2b is believed to adopt a Z geomeLry, only one isomer was observable by H-NMR spectroscopy (d.r. >98 2). 

Page et al. (see [298] and references therein) have shown that generally excellent stereocontrol in organic reactions can be obtained by using DITOX (1,3-dithiane-l-oxide) derivatives as chiral auxiliaries. The one-pot stereo-controlled cycloalkanone synthesis given here outlines some aspects of the chemistry worked out for efficient acylation-alkylations steps. Of note are the use of N-acyl imidazoles under mixed base (sodium hexamethyldisilazide/n-butyllithium) conditions to yield the lithium enolates of 2-acyl-l,3-dithiane-l-oxides) and the sequential alkylation-cyclization of the latter (steps (iv) and (v)). 

Since most of the synthetically useful enolate anions described in the previous section are prepared by the reactions of enolizable substrates with alkali metal amide bases, it is appropriate to note a few structures of these amide bases. The common bases in synthetic organic chemistry include LDA and LHMDS. The structures of both of these bases are known as the THF solvates.Both of these compounds form bis-solvated dimers corresponding to structure (201). The diethyl ether solvate of LHMDS also forms a bis-solvated dimer (202).Sodium hexamethyldisilazide crystallizes as an unaggregated monomer from benzene solution.Two different cryst line forms of KHMDS are known as the polymeric dioxane solvate (203), ° and the unsolvated dimer (204). ... 

The sodium enolate of A -acyloxazolidone (159) reacts with sodium hexamethyldisilazide and PNBSA and followed by treatment with TMSC1 affords the diazo compound 160.73... 

Sodium dithionite, 456-458 Sodium enolates, 445 Sodium formate, 458 Sodium hexamethyldisilazide, 453 Sodium hydride, 337, 458-459 Sodium hydridoundecacarbonyltri-ferrate, 390... 

Enolates can also be used to assemble bicyclo[4.2.0] octanes (Scheme 19.25). Lee and co-workers treated trien-one 100 with sodium hexamethyldisilazide (NaHMDS) in refluxing 1,2-dimethoxyethane for 12 hours to produce tricyclic product 101 of unspecified stereochemistry in 47% yield. Several features contribute to the interest of this reaction. The 6ti-electrocyclization of the sodium enolate that is derived from 100 evidently does not compete with the 871-electrocyclization. The enolate may facilitate the 8ti-/671-cascade process in a similar way as with the anionic... 

Related thermodynamic enolization control has been observed using metallated hexamethyldisilazide to give the more substituted bromomagnesium ketone enolates. Metallation reactions of HMDS to yield Li, K, and Na derivatives are well known and the resulting nonnucleophilic bases have found extensive applications in organic synthesis (see Lithium HexamethyldisUaade, Potassium Hexamethyldisilazide, Sodium Hexamethyldisilazide). ... 

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