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Enolate Acidity, Stability and Geometry

In general, alkyl hydrogens are not very aeidie. However, alkyl hydrogens adjacent to carbonyl groups can be deprotonated by strong bases to give enolate anions, e.g., for acetone. [Pg.163]

Compare electrostatic potential maps for propane, acetone and 2,4-pentanedione, and identify the most positively-charged acidic hydrogen(s) in each. Is there a correlation between electrostatic potential and pK (see table at right)  [Pg.163]

How many different enolates may arise from deprotonation of 2,4-pentanedione Draw Lewis structures for each, and predict which is likely to be the most stable. Check your conclusions by examining the energies of the different possible enolates (enolate A, B...). Is the most stable enolate that derived from deprotonation of the most electron-poor hydrogen Compare the electrostatic potential maps of the anions with each other and with your Lewis structures. Revise your drawings to be consistent with the maps. Why is one of the enolates preferred over the others  [Pg.163]

Electrostatic potential map for 2,4-pentanedione shows positively-charged regions (in blue) as likely acidic sites. [Pg.163]


In recent organic synthesis, stereoselective aldol condensations has been performed under two different conditions. Under the influence of acid, stabilized enol derivatives, enolsilanes (M = SiMe3), can condense with aldehydes or acetals in a stereoselective fashion [Eq. (12)]. In this reaction the role of the acid is to activate aldehydes or acetals. Alternatively, under basic conditions, the same process can be carried out directly with aldehydes and reactive, preformed metal enolates (M = Li, MgL, ZnL, AIL2, BL2, etc.) of defined geometry. [Pg.265]

Retention of geometry, perfect chirality transfer, and high reactivity have been observed by the reaction of the chelated Zn enolate of amino acid ester 53 even when PPhs was used [23]. In addition, the non-stabilized enolate 53 was found to be very reactive. Reaction of the allylic carbonates 54 and 56 with the enolate 53 gave 55 and 57 with perfect chirality transfer and high diastereoselectivity. The carbonates and the enolates are highly reactive and the reaction starts even at —78 °C. Lower selectivity was observed by the reaction of the corresponding allylic acetate. [Pg.440]


See other pages where Enolate Acidity, Stability and Geometry is mentioned: [Pg.159]    [Pg.163]    [Pg.169]    [Pg.250]    [Pg.252]    [Pg.159]    [Pg.163]    [Pg.169]    [Pg.250]    [Pg.252]    [Pg.176]    [Pg.22]    [Pg.199]    [Pg.201]    [Pg.320]    [Pg.320]    [Pg.910]    [Pg.398]    [Pg.103]    [Pg.263]    [Pg.910]    [Pg.239]    [Pg.1318]    [Pg.10]    [Pg.1127]    [Pg.193]    [Pg.290]    [Pg.511]    [Pg.951]    [Pg.76]   


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Acid stabilization

Acids stability

Enolate Stabilized

Enolate geometry

Enolates stabilization

Enolates stabilized

Enolates stabilizing

Enolic acids

Enols acidity

Enols stability

Stability enolate

Stability enolates

Stabilized Enols

Stabilizers acid

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