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Organic Chemistry
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- suggested using an enamine intermediate because it's a weaker base (it's neutral!!) and so more likely to act as a Michael donor (1,4- addition)
- if nucleophile adds reversibly, the 1,4-overall thermodynamic product dominates (note resonance in 1,4 enolate)
- NaOH over H2O, aldol addition gives a beta-hydroxy aldehyde or ketone
- the initial enol is the result of 'conjugate' or 1,4-addition. The enol tautomerizes to the more stable keto form
- aldol reaction occurs. The product (a β-hydroxycarbonyl) features both aldehyde and alcohol groups
- has a lower activation energy for formation (carbonyl has larger delta plus). If nucleophile adds irreversibly, the 1,2-kinetic product dominates
- gives cyclohexenones and is a Michael addition followed by internal Aldol condensation
- the formation of a conjugated (stable) pi system. Aldol addition products are often difficult to isolate, even at low T
- more acidic than an aldehyde, ketone, or ester, because its conjugate base is stabilized (resonance) by the presence of the two carbonyls
- Two different esters (or an ester and a ketone!) can be used, but one should have no alpha hydrogens, for example a benzoate, formate, carbonate, or oxalate
- weakly acidic, hence esters can be deprotonated to give an ester enolate anion, which is a strong nucleophile
- an ester molecule (with electrophilic carbonyl group) undergoes nucleophilic acyl substitution by an ester enolate
- see what groups are added to the acetic acid product, then alkylate malonic ester with R-X and R-X, hydrolyze, decarboxylate
- aldol addition plus alsol condensation, gives alpha beta unsaturated aldehyde or ketone
- retro aldol mechanism can work, carbanion leaving group acceptable due to resonance stabilization of enolate, done by breaking alpha beta bond
- enolates. Kinetic product forms faster, thermodynamic is more stable (more substituted c=c; favored at high T)
- top arrow is aldol addition, bottom arrow is aldol condensation
- combine two or more molecules, often with the loss of a small molecule such as water, an alcohol, CO2, or N2
- is deprotonated in a strongly exothermic step (strong base present !!!), which DRIVES THE REACTION forwards
- electrophilic carbon atoms. The beta-C is electrophilic because it shares the δ+ of the carbonyl C (resonance).