Deprotonation of carbonyl compounds

There have been numerous studies of the rates of deprotonation of carbonyl compounds. These data are of interest not only because they define the relationship between thermodynamic and kinetic acidity for these compounds, but also because they are necessary for understanding mechanisms of reactions in which enolates are involved as intermediates. Rates of enolate formation can be measured conveniently by following isotopic exchange using either deuterium or tritium ... 

Deprotonation of carbonyl compounds by chiral amide bases followed by trapping with silylating agents or aldehydes has become a common method for de-symmetrizing prochiral and conformationally locked 4-substituted cyclohexanones and bicyclic ketones. The literature through 1997 has been reviewed [45]. 

The preparation and reactions of alkylzinc enolates have been studied. The main methods for their synthesis are metal exchange between hthium enolates and zinc chloride, deprotonations of carbonyl compounds with... 

Examination of electronic and thermodynamic factors in the aforementioned conventional enolate formation revealed that steric factors were of fundamental importance in fhe reaction. One alternative is to complex a carbonyl compound with a bulky Lewis acid (Fig. 6.13). Bulky aluminum reagents usually form relatively stable 1 1 complexes irreversibly wifh carbonyl compounds. We first hypothesized that even in the presence of a strong base (LDA or LTMP), a steric environment applied in the aluminum-carbonyl complex would kinetically adjust site-selective deprotonation of carbonyl compounds which offer multiple sites for enohzation and kinetically stabilize fhe resulting bulky enolates by retarding the rate of proton transfer or other undesirable side reactions. These fundamental considerations found particular application in fhe formation and reaction of novel aluminum enolates. 

Alkali Metal Enolates by Deprotonation of Carbonyl Compounds... 

Deprotonation of carbonyl compounds by lithium dialkylamide bases is the single most common method of forming alkali enolates. Four excellent reviews have already been published. " Sterically hindered amide bases are employed to retard nucleophilic attack on the carbonyl group. The most common and generally useful bases are (i) lithium diisopropylamide (LDA 5) (ii) lithium isopropylcyclo-hexylamide (LICA 6) (iii) lithium 2,2,6,6-tetramethylpiperidide (LITMP 7) (iv) lithium hexamethyldisilylamide (LHMDS 8) and (v) lithium tetramethyldiphenyldisilylamide (LTDDS 9). Bases that are not amides include sodium hydride, potassium hydride and triphenylmethyllithium. 

There have been numerous studies of the rates of deprotonation of carbonyl compounds. These data are of interest not only because they define the relationship... 

For deprotonation of carbonyl compounds to form enolate ions, see Section 8.4.3... 

Base for a-Deprotonation of Carbonyl Compounds. Potassium hexamethyldisilazide, KN(TMS)2 (KHMDS) has been... 

Alkali Metal Enolates by Deprotonation of Carbonyl Compounds 1.422 Alkali Metal Enolates by Addition to a,fi-Unsaturated Carbonyl Compounds... 

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