Metalations potassium hexamethyldisilazide

Potassium hydride and potassium hexamethyldisilazide are the most commonly used metal sources to generate the alkoxide . But recently, the indium(I)-mediated tandem carbonyl addition-oxy-Cope rearrangement of y-pentadienyl anions to cyclohexenones and conjugated aromatic ketones has been reported. For example, indium alkoxide 8.32, obtained after the addition of 5-bromopenta-1,3-diene (8.31) to the aromatic conjugated ketones 8.30, undergoes a spontaneous oxy-Cope rearrangement to give 8.33 in 55% yield (Scheme 8.9). 

Potassium hexamethyldisilazide, KHMDS, has been used successfully in the past for a-deprotonation of sulfoxides. Aiming to probe the nature of the transition state in the reaction of a-metalated (i )-methyl //-tolyl sulfoxide with A -(benzylidene) aniline under kinetic conditions, the effect of the choice of the bases for the a-deprotonation on the reactivity and diastereoselectivity was studied, using LDA, LHMDS, NaHMDS, and KHMDS. Best yields anddiastereoselectivities (90%, 84 16) were achieved with LDA, whereas LHMDS showed diminished reactivity (50%) without a loss of diastereoselectivity (87 13). Improved yields and lower diastereoselectivities were recorded in reactions mediated by NaHMDS and KHMDS, providing the amine in 60% (dr 81 19) and 77% (dr 69 31) yields and diastereoselectivities, respectively (eq 64). 

Synthetically important alkali—metal amides Lithium, sodium, and potassium hexamethyldisilazides, diisopropylamides, and tetramethylpiper-idides 13AG(E)11470. 

Some catalysts such as potassium hexamethyldisilazide (K[NSiMc3]2) lead to high molar mass PTMC or TMC-based block copolymers with high efficiency and desired end groups. The polymerisation can be carried out in solution at room temperature (Lemmouchi et al., 2008). The resulting polymers contain no traces of metal... 

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). ... 

Interesting examples of simple substituted heterometallic species are [(thf)M p-N(SiMe3)2 2M (th 2] (M/M = Li/Na, Li/K and Na/K) which were obtained from solutions of 1 1 mixtures of the metal salts.The unsolvated ( LiXtSiMe J , K- lSiXleO, ), has a polymeric, one-dimensional chain structure formed by alternating lithium and potassium centres bridged through the hexamethyldisilazides (Li—N= 1.935(1) A and K—N = 2.86(1) A) with linear coordination at K and almost linear coordination (N-Li= 176.4(3)°) atLi. ... 

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