-formed by treating aldehyde, ketone, or ester (each which has at least 1 alpha-H) w/ base

-most of neg. charge in enolate anion is on O

-nucleophiles in Sn2 rxns and C=O addition rxns

-most imp. rxn of enolate anions=nucleophilic addition to C=O group of another molecule of same/different compound

*can be catalyzed by A or B but B more common

1. formation of resonance stabilized enolate anion

2. C=O addition gives TCAI

3. proton transfer to O- completes aldol rxn

1. A-catalyzed equilibration of keto and enol forms

2. proton transfer from HA to C=O group of a 2nd molecule of aldehyde or ketone

3. attack of enol of 1 molecule on protonated C=O group of another molecule

4. proton transfer to A- completes rxn

-aldol products easily dehydrated to alpa, beta-unsaturated aldehydes/ketones

-aldol rxns=reversible and little aldol present at equilibrium

-Keq for dehydration generally large

-if rxn conditions bring about dehydration, good yields of product obtained

-1 kind of molecule provides enolate anion and another kind provides C=O group

-most successful if:

*1 of reactants has no alpha-H and therefore can't form enolate anion

*other reactant has more reactive C=O group (namely an aldehyde)

-intramolecular aldol rxns most successful for formation of 5/6 membered rings

*nitro groups can also be used

-esters form enolate anions which participate in nucleophilic acyl substitution

-product of Claisen is beta-ketoester

1. formation of enolate anion

2. attack of enolate anion on C=O C gives TCAI

3. collapse of TCAI gives beta-ketoester and alkoxide ion

4. A-B rxn drives rxn to completion

-btwn 2 diff. esters, each w/ alpha-Hs, gives mixtures of products and aren't useful

-useful crossed Claisen possible if there's big difference in reactivity btwn the 2 esters

*1 of them has no alpha-Hs, usually used in excess

-route to ketones

-Rxns 1 and 2: Claisen then acidification

-3 and 4: saponification and acidification

-5: thermal decarboxylation

-value of enamines is that beta-C is nucleophilic

*enamines undergo Sn2 rxns w/ -CH3 and 1' haloalkanes, alpha-haloketones, and alpha-haloesters

*treatment of enamine w/ 1 equivalent of alkylating agent gives iminium halide

*hydrolysis of iminium halide gives alkylated aldehyde/ketone

-useful for preparation of mono- and disubstituted acetones

1. formation of enolate anion of AAE

2. alkylation w/ allyl bromide

3. and 4. saponification then acidification

5. thermal decarboxylation

-to prepare disubstituted acetone, treat monoalkylated AAE w/ 2nd mole of base, etc

-identical to AAE except that starting material is beta-diester rather than beta-ketoester

-nucleophilic addition of enolate anion to alph, beta-unsaturated C=O compound

1. proton transfer to base

2. addition of Nu to beta-C of alpha, beta-unsaturated C=O compound

3. proton transfer to HB gives enol

4. tautomerism of less stable enol form to the more stable keto form

-resonance stabilized enolate anions and enamines=weak Bs, react slowly w/ alpha,beta-unsaturated

-OrganoLi and Grignard=strong Bs, add rapidly to C=O groups and give primarily 1,2-addition

-thermodynamic vs kinetic control

-addition of Nu=irreversible for strongly basic C Nus

-enamines also participate in Michael rxns

-undergo conjugate addition to alpha,beta-unsaturated aldehydes/ketones in rxn closely related to Michael

-unique among organometallic compounds cuz give almost exclusively 1,4-addition

*other organometallic compounds, including Grignard, add to C=O C by 1,2-addition

-w/ strong enough B, enolate anion formation can be driven to completion

*common B used=LDA, prepared by dissolving diisopropylamine in THF and treating soln w/ butyl Li

*using molar equivalent of LDA can completely convert aldehyde, ketone or ester to its corresponding enolate anion

-for ketones w/ 2 sets of nonequivalent alpha-Hs there's high degree of regioselectivity in formation of enolate anion  (depends on experimental conditions)

-most imp. factor determining composition of enolate anion mixture is if rxn is under kinetic (rate) or thermodynamic (equilibrium) control

-thermodynamic: conditions permit establishment of equilibrium btwn 2 or more products of rxn

*composition of mixture determined by stabilities of products

-kinetic: conditions where composition of product mixture is detemined by relative rates of product formation