Organic Chemistry 2 · Carbonyl and enolate chemistry
Aldol addition and condensation: practice problems
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- (E)-Benzalacetone from benzaldehyde and acetone
- Aldol addition — ethanal donor–acceptor bond formation
- Aldol condensation — preformed E1cb elimination stage
- Aldol addition — acetone self-addition
- Crossed aldol addition — acetone and benzaldehyde in base
- Crossed aldol addition — propanal hydroxymethylation
- Intramolecular aldol addition — five-membered dialdehyde closure
- Intramolecular aldol addition — six-membered diketone closure
- Retro-aldol reaction — diacetone alcohol cleavage
Draw the mechanism 79
- Aldol addition — ethanal donor–acceptor bond formationDraw aldol C–C bond formation and protonation while retaining the donor carbonyl.
- Aldol condensation — preformed E1cb elimination stageDraw the bond-reorganization stage of E1cb aldol dehydration.
- Aldol addition — acetone self-additionComplete the reversible self-aldol of a ketone from neutral starting molecules.
- Crossed aldol addition — acetone and benzaldehyde in baseAssign the enolizable ketone donor and the non-enolizable aromatic aldehyde acceptor.
- Crossed aldol addition — propanal hydroxymethylationUse formaldehyde as a non-enolizable acceptor while preserving the donor aldehyde.
- Intramolecular aldol addition — five-membered dialdehyde closureCount the five ring atoms and keep the donor aldehyde outside the new ring.
- Intramolecular aldol addition — six-membered diketone closureTrack a ketone acceptor and distinguish ring closure from terminal-site intermolecular addition.
- Retro-aldol reaction — diacetone alcohol cleavageChoose alkoxide-initiated C–C cleavage instead of dehydration and recover both neutral carbonyl partners.
- Aldol condensation — dehydration of the aldol productForm an enolate, then lose hydroxide to make a C=C bond next to the carbonyl.
- Aldol condensation — acidic dehydration to mesityl oxideDistinguish water-leaving acid dehydration from hydroxide-leaving E1cb chemistry.
- Crossed aldol addition — neutral enol attack in acidCouple acid enolization and acceptor activation with an octet-preserving aldol arrow relay.
- Claisen–Schmidt condensation — double condensation to dibenzalacetoneMaintain two independent alpha sites and track the changing hydroxide oxygen through two complete aldol/dehydration cycles.
- Aldol condensation of acetaldehyde to crotonaldehydeDraw the hydroxide-catalysed self-aldol addition of acetaldehyde to 3-hydroxybutanal and its E1cB dehydration to but-2-enal.
- Directed crossed aldol addition of propiophenone to pivalophenone (LDA)Draw the directed crossed aldol addition: LDA converts propiophenone completely into its enolate, the enolate adds to pivalophenone at −78 °C, and the ammonium chloride quench protonates the alkoxide to give 3-hydroxy-2,4,4-trimethyl-1,3-diphenylpentan-1-one.
- Intramolecular aldol condensation of 5-oxohexanalDraw the base-catalysed intramolecular aldol addition of 5-oxohexanal that closes a six-membered ring, then the E1cB dehydration that gives cyclohex-2-en-1-one.
- 2-Methylcyclohex-2-en-1-one from 5-oxoheptanalDraw the intramolecular aldol condensation of 5-oxoheptanal: ketone enolate formation on the ethyl side, six-membered ring closure onto the aldehyde, protonation, second enolization and E1cB dehydration to 2-methylcyclohex-2-en-1-one.
- 1-Acetylcyclopentene from 6-oxoheptanalDraw the intramolecular aldol condensation of 6-oxoheptanal: internal ketone enolate formation, five-membered ring closure onto the aldehyde, protonation, second enolization and E1cB dehydration to 1-acetylcyclopentene.
- Mesityl oxide from acetone in sulfuric acidDraw the sulfuric acid-catalysed self-condensation of acetone: enol formation, attack on a protonated acetone, and E1 dehydration of the aldol to mesityl oxide.
- (E)-But-2-enal from acetaldehyde in acidDraw the HCl-catalysed aldol condensation of acetaldehyde: enol formation, attack on a protonated acetaldehyde, deprotonation to 3-hydroxybutanal, and acid-catalysed dehydration through the enol to (E)-but-2-enal.
- (E)-2-Benzylidenecyclohexanone from cyclohexanoneDraw the hydroxide-catalysed mono-condensation of cyclohexanone with one equivalent of benzaldehyde to (E)-2-benzylidenecyclohexanone.
- anti-2-[Hydroxy(phenyl)methyl]cyclohexan-1-one (boron)Draw the Bu2BOTf/i-Pr2NEt aldol of cyclohexanone with benzaldehyde: boron activation, the ring-locked E boron enolate, Zimmerman–Traxler chair addition and the H2O2 workup to anti-2-[hydroxy(phenyl)methyl]cyclohexan-1-one.
- anti-1-Hydroxy-2-methyl-1-phenylpentan-3-one (Cy2BCl)Draw the Cy2BCl/Et3N aldol of pentan-3-one with benzaldehyde: boron activation, E boron enolate, Zimmerman–Traxler chair addition and the H2O2 workup to anti-1-hydroxy-2-methyl-1-phenylpentan-3-one.
- syn-1-Hydroxy-2-methyl-1-phenylpentan-3-one (boron aldol)Draw the Bu2BOTf/i-Pr2NEt aldol of pentan-3-one with benzaldehyde: boron activation, Z boron enolate, Zimmerman–Traxler chair addition and the H2O2 workup to syn-1-hydroxy-2-methyl-1-phenylpentan-3-one.
- syn-3-Hydroxy-2,4-dimethyl-1-phenylpentan-1-one (boron)Draw the Bu2BOTf/i-Pr2NEt aldol of propiophenone with 2-methylpropanal: boron activation, Z boron enolate, Zimmerman–Traxler chair addition and the H2O2 workup to syn-3-hydroxy-2,4-dimethyl-1-phenylpentan-1-one.
- (E)-2-Ethylhex-2-enal from butanal self-condensationDraw the self-aldol condensation of butanal in hot NaOH: enolate formation, addition to a second butanal, protonation, second enolization and E1cB dehydration to (E)-2-ethylhex-2-enal.
- (E)-3-Methyl-4-phenylbut-3-en-2-one from butanone in acidDraw the HCl-catalysed aldol condensation of butanone with benzaldehyde at the methylene side: enol formation, attack on protonated benzaldehyde, second enolization and enol-assisted loss of water to (E)-3-methyl-4-phenylbut-3-en-2-one.
- (E)-1-Phenylpent-1-en-3-one from butanone in baseDraw the base-catalysed crossed aldol condensation of butanone with benzaldehyde at the methyl side: methyl enolate, addition, protonation, second enolization and E1cB loss of hydroxide to (E)-1-phenylpent-1-en-3-one.
- 1-Hydroxy-1-phenylpentan-3-one by kinetic directed aldolDraw the directed aldol of butanone: LDA forms the kinetic (methyl) enolate at −78 °C, which adds to benzaldehyde; NH4Cl workup gives 1-hydroxy-1-phenylpentan-3-one.
- (E)-Chalcone from acetophenone and benzaldehydeDraw the base-catalysed condensation of acetophenone with benzaldehyde to (E)-chalcone, including the aldol addition, the second enolization and the E1cB loss of hydroxide.
- (E)-Cinnamaldehyde from acetaldehyde and benzaldehydeDraw the crossed aldol condensation of acetaldehyde with benzaldehyde in NaOH: acetaldehyde enolate, addition to benzaldehyde, protonation, second enolization and E1cB dehydration to (E)-cinnamaldehyde.
- (E)-Benzalacetone from benzaldehyde and acetoneDraw the Claisen–Schmidt condensation of acetone with benzaldehyde: enolate formation, aldol addition, protonation, second enolization and E1cB loss of hydroxide to (E)-benzalacetone.
- (E)-α-Methylcinnamaldehyde from propanal and benzaldehydeDraw the crossed aldol condensation of propanal with benzaldehyde to (E)-2-methyl-3-phenylprop-2-enal, from enolate formation through the E1cB loss of hydroxide.
- 2-(Hydroxymethyl)cyclohexan-1-one from cyclohexanoneDraw the carbonate-catalysed crossed aldol addition of cyclohexanone to formaldehyde: enolate formation by carbonate, addition to formaldehyde and protonation by bicarbonate to 2-(hydroxymethyl)cyclohexan-1-one.
- 2-Cyclohexylidenecyclohexan-1-one from cyclohexanoneDraw the self-aldol condensation of cyclohexanone in hot NaOH: enolate formation, addition to a second cyclohexanone, protonation, second enolization and E1cB dehydration to 2-cyclohexylidenecyclohexan-1-one.
- Ethyl trans-3-phenyloxirane-2-carboxylate by the Darzens reactionDraw the Darzens condensation of ethyl chloroacetate with benzaldehyde: enolate formation, aldol-type addition, and intramolecular SN2 ring closure to the trans glycidic ester.
- Ethyl 1-oxaspiro[2.5]octane-2-carboxylate by DarzensDraw the Darzens glycidic ester condensation of ethyl chloroacetate with cyclohexanone: tert-butoxide enolization, addition to the ketone and intramolecular SN2 closure to ethyl 1-oxaspiro[2.5]octane-2-carboxylate.
- (E,E)-Dibenzalacetone: the second condensationDraw the second Claisen–Schmidt condensation: the methyl enolate of (E)-benzalacetone adds to a second benzaldehyde and loses hydroxide by E1cB to give (E,E)-dibenzalacetone.
- (2E,5E)-2,5-DibenzylidenecyclopentanoneDraw the double Claisen–Schmidt condensation of cyclopentanone with two benzaldehydes: enolate, addition, protonation and E1cB dehydration at one α-carbon, then the same sequence at the other α-carbon to (2E,5E)-2,5-dibenzylidenecyclopentanone.
- 4-Hydroxy-5-methylhexan-2-one by a directed aldolDraw the directed crossed aldol of acetone with 2-methylpropanal: complete LDA enolization of acetone, addition of the enolate to the aldehyde, and NH4Cl workup to 4-hydroxy-5-methylhexan-2-one.
- Ethyl 3-hydroxy-3-phenylpropanoate by a directed ester aldolDraw the directed aldol of ethyl acetate with benzaldehyde: LDA enolization at −78 °C, addition of the lithium enolate to benzaldehyde, and NH4Cl workup to ethyl 3-hydroxy-3-phenylpropanoate.
- (E)-4-Methoxycinnamic acid by Doebner condensationDraw the Doebner condensation of anisaldehyde with malonic acid: piperidine forms the malonic acid enolate, which adds to the aldehyde; after protonation and carboxylate formation, decarboxylative elimination gives (E)-4-methoxycinnamic acid.
- (E)-2-Methylpent-2-enal by E1cB dehydrationDraw the hydroxide-promoted E1cB dehydration of 3-hydroxy-2-methylpentanal to (E)-2-methylpent-2-enal: enolate formation, then loss of hydroxide from the β-carbon.
- Evans syn aldol: propanoyl oxazolidinone + benzaldehydeDraw the Evans boron aldol of (4S)-4-benzyl-3-propanoyl-1,3-oxazolidin-2-one with benzaldehyde: boron activation, Z boron enolate, auxiliary-controlled Zimmerman–Traxler chair addition and the H2O2 workup to the Evans syn aldol adduct.
- Evans syn aldol: propanoyl oxazolidinone + 2-methylpropanalDraw the Evans boron aldol of (4S)-4-benzyl-3-propanoyl-1,3-oxazolidin-2-one with 2-methylpropanal: boron activation, Z boron enolate, auxiliary-controlled Zimmerman–Traxler chair addition and the H2O2 workup to the Evans syn aldol adduct.
- 2-Nitro-1-phenylethanol by the Henry reactionDraw the hydroxide-catalysed Henry reaction of nitromethane with benzaldehyde: nitronate formation, C–C bond formation at the aldehyde, and protonation to 2-nitro-1-phenylethanol.
- (E)-β-Nitrostyrene from 2-nitro-1-phenylethanolDraw the acetylation of 2-nitro-1-phenylethanol by acetic anhydride and the E1cB elimination of acetate through the nitronate to (E)-β-nitrostyrene.
- 1-(4-Methoxyphenyl)-2-nitropropan-1-ol by the Henry reactionDraw the hydroxide-catalysed Henry reaction of nitroethane with 4-methoxybenzaldehyde: nitronate formation, addition to the aldehyde carbon and protonation to 1-(4-methoxyphenyl)-2-nitropropan-1-ol.
- Cyclohex-1-ene-1-carbaldehyde from heptanedialDraw the intramolecular aldol condensation of heptanedial: enolate formation at C2, six-membered ring closure onto the C7 aldehyde, protonation, second enolization and E1cB dehydration to cyclohex-1-ene-1-carbaldehyde.
- 3-Methylcyclopent-2-en-1-one from hexane-2,5-dioneDraw the intramolecular aldol condensation of hexane-2,5-dione: methyl enolate formation, five-membered ring closure, protonation, second enolization and E1cB dehydration to 3-methylcyclopent-2-en-1-one.
- 3-Methylcyclohex-2-en-1-one from heptane-2,6-dioneDraw the intramolecular aldol condensation of heptane-2,6-dione: methyl enolate formation, six-membered ring closure, protonation and E1cB dehydration to 3-methylcyclohex-2-en-1-one.
- Cyclopent-1-ene-1-carbaldehyde from hexanedialDraw the intramolecular aldol condensation of hexanedial: C2 enolate formation, five-membered ring closure onto the other aldehyde, protonation and E1cB dehydration to cyclopent-1-ene-1-carbaldehyde.
- 3-Hydroxy-2,2-dimethyl-3-phenylpropanal by crossed aldolDraw the crossed aldol addition of 2-methylpropanal to benzaldehyde with catalytic NaOH: enolate formation, addition and protonation to 3-hydroxy-2,2-dimethyl-3-phenylpropanal, and see why it cannot dehydrate.
- 3-Hydroxy-2,2-dimethylpropanal from 2-methylpropanal and formaldehydeDraw the carbonate-catalysed crossed aldol of 2-methylpropanal with formaldehyde to 3-hydroxy-2,2-dimethylpropanal: enolate formation, attack on formaldehyde and protonation.
- 3-Benzylidenepentane-2,4-dione by KnoevenagelDraw the Knoevenagel condensation of pentane-2,4-dione with benzaldehyde in piperidinium acetate: enolate addition, protonation, re-enolization and E1cB loss of hydroxide to 3-benzylidenepentane-2,4-dione.
- Ethyl (E)-2-cyano-3-phenylacrylate by KnoevenagelDraw the piperidine-catalysed Knoevenagel condensation of ethyl cyanoacetate with benzaldehyde: enolate formation, addition, protonation, a second deprotonation and E1cB loss of hydroxide.
- Diethyl 2-benzylidenemalonate by Knoevenagel condensationDraw the piperidine-catalysed Knoevenagel condensation of diethyl malonate with benzaldehyde through the enolate addition and E1cB dehydration to diethyl 2-benzylidenemalonate.
- 2-Cyclohexylidenemalononitrile by Knoevenagel condensationDraw the acetate-catalysed Knoevenagel condensation of malononitrile with cyclohexanone: deprotonation, addition to the ketone, protonation, and E1cB dehydration to 2-cyclohexylidenemalononitrile.
- syn-3-Hydroxy-2-methyl-1,3-diphenylpropan-1-one (Li aldol)Draw the LDA aldol of propiophenone with benzaldehyde: the Z lithium enolate, its chair (Zimmerman–Traxler) addition to the aldehyde and the NH4Cl workup to syn-3-hydroxy-2-methyl-1,3-diphenylpropan-1-one.
- syn-1-Hydroxy-2,4,4-trimethyl-1-phenylpentan-3-oneDraw the Heathcock LDA aldol of 2,2-dimethylpentan-3-one with benzaldehyde: the Z lithium enolate forced by the tert-butyl group, the chair (Zimmerman–Traxler) addition and the NH4Cl workup to the syn aldol.
- 4-(Dimethylamino)butan-2-one by the Mannich reactionDraw the Mannich reaction of acetone, formaldehyde and dimethylamine: iminium ion formation, acid-catalysed enolization of acetone, C–C bond formation and deprotonation to 4-(dimethylamino)butan-2-one.
- 2-(Piperidin-1-ylmethyl)cyclopentan-1-one by MannichDraw the Mannich reaction of cyclopentanone, formaldehyde and piperidine with catalytic HCl: iminium ion formation, enolate formation by piperidine and C–C bond formation to 2-(piperidin-1-ylmethyl)cyclopentan-1-one.
- (E)-4-Methoxychalcone from anisaldehyde and acetophenoneDraw the Claisen–Schmidt condensation of acetophenone with anisaldehyde: acetophenone enolate, addition, protonation, second enolization and E1cB loss of hydroxide to (E)-4-methoxychalcone.
- Kinetic aldol of 2-methylcyclohexanone with benzaldehydeDraw the directed aldol of 2-methylcyclohexan-1-one: LDA removes the C6 hydrogen to give the kinetic enolate, which adds to benzaldehyde; NH4Cl workup gives 2-(hydroxy(phenyl)methyl)-6-methylcyclohexan-1-one.
- 3-Hydroxy-1,3-diphenylpropan-1-one by a Mukaiyama aldolDraw the TiCl4-mediated Mukaiyama aldol of the trimethylsilyl enol ether of acetophenone with benzaldehyde: Lewis-acid activation, C–C bond formation, silyl transfer and aqueous workup to 3-hydroxy-1,3-diphenylpropan-1-one.
- 2-[Hydroxy(phenyl)methyl]cyclohexan-1-one, Mukaiyama aldolDraw the TiCl4-promoted Mukaiyama aldol of 1-(trimethylsilyloxy)cyclohexene with benzaldehyde: Lewis-acid activation, C–C bond formation, silyl transfer to chloride and aqueous workup to 2-[hydroxy(phenyl)methyl]cyclohexan-1-one.
- [(E)-2-Nitroprop-1-enyl]benzene by Henry condensationDraw the acetate-buffered Henry condensation of nitroethane with benzaldehyde: nitronate addition, protonation, a second nitronate and E1cB loss of hydroxide to [(E)-2-nitroprop-1-enyl]benzene.
- 1-Acetyl-2-methylcyclohexene from nonane-2,8-dioneDraw the intramolecular aldol condensation of nonane-2,8-dione: internal (C3) enolate formation, six-membered ring closure, protonation, second enolization and E1cB dehydration to 1-acetyl-2-methylcyclohexene.
- Octalone from 2-(3-oxobutyl)cyclohexan-1-oneDraw the aldol ring closure of 2-(3-oxobutyl)cyclohexan-1-one: side-chain methyl enolate formation, six-membered ring closure onto the ring ketone, protonation, second enolization and E1cB dehydration to the octalone.
- (E)-Cinnamic acid by the Perkin reactionDraw the Perkin reaction of benzaldehyde with acetic anhydride and sodium acetate: anhydride enolate formation, aldol addition, intramolecular acetyl transfer, and E1cB loss of acetate to (E)-cinnamic acid.
- (E)-2-Methyl-3-phenylprop-2-enoic acid by Perkin reactionDraw the Perkin reaction of benzaldehyde with propanoic anhydride and sodium propanoate: anhydride enolate, aldol addition, acyl transfer, mixed anhydride, E1cB loss of propanoate and acidic hydrolysis to (E)-2-methyl-3-phenylprop-2-enoic acid.
- 3-Phenylcyclohex-2-en-1-one from 1-phenylhexane-1,5-dioneDraw the intramolecular aldol condensation of 1-phenylhexane-1,5-dione: methyl enolate formation, six-membered ring closure onto the aryl ketone, protonation, second enolization and E1cB dehydration to 3-phenylcyclohex-2-en-1-one.
- (R)-4-Hydroxy-4-(4-nitrophenyl)butan-2-one by proline aldolDraw the L-proline-catalysed aldol of acetone with 4-nitrobenzaldehyde: iminium and enamine formation, the Houk–List C–C bond formation with proton transfer from the acid, and iminium hydrolysis to (R)-4-hydroxy-4-(4-nitrophenyl)butan-2-one.
- anti-2-[Hydroxy(4-nitrophenyl)methyl]cyclohexanone (proline)Draw the L-proline-catalysed aldol of cyclohexanone with 4-nitrobenzaldehyde: iminium and enamine formation, the Houk–List C–C bond formation that sets the anti pair, and iminium hydrolysis to the anti aldol.
- Retro-aldol cleavage of diacetone alcohol into acetoneDraw how hot aqueous hydroxide splits diacetone alcohol into two acetone molecules: alkoxide formation, C–C bond cleavage to an enolate, and protonation of the enolate on carbon.
- Diacetone alcohol from acetone with barium hydroxideDraw the barium hydroxide-catalysed self-aldol addition of acetone to diacetone alcohol (4-hydroxy-4-methylpentan-2-one) and explain why the equilibrium must be pulled toward the product.
- 3-Hydroxy-2-methylpentanal from propanalDraw the hydroxide-catalysed self-aldol addition of propanal: enolate formation, attack on a second propanal and protonation to 3-hydroxy-2-methylpentanal.
- Stobbe condensation of benzophenone with diethyl succinateDraw the Stobbe condensation of benzophenone with diethyl succinate: enolate formation, addition to benzophenone, alkoxide attack on the far ester to a γ-lactone, loss of ethoxide, E1cB lactone opening and acid workup to the half-ester acid.
- (E)-4-(Thiophen-2-yl)but-3-en-2-one from acetoneDraw the Claisen–Schmidt condensation of acetone with thiophene-2-carbaldehyde: acetone enolate, addition, protonation, second enolization and E1cB dehydration to (E)-4-(thiophen-2-yl)but-3-en-2-one.
- Wieland–Miescher ketone by intramolecular aldolDraw the aldol ring closure of 2-methyl-2-(3-oxobutyl)cyclohexane-1,3-dione: methyl enolate formation, six-membered ring closure onto a ring ketone, protonation, second enolization and E1cB dehydration to the Wieland–Miescher ketone.
Predict the product 13
- Crossed aldol addition — acetone enolate and benzaldehydePredict a crossed aldol addition connectivity without an implicit dehydration.
- Heating the aldol of acetaldehydePredict the aldol condensation product of acetaldehyde.
- Alkene geometry of an aldol condensationPredict the alkene geometry formed in a thermodynamic aldol condensation.
- Claisen–Schmidt product of benzaldehyde and acetone (1:1)Predict the Claisen–Schmidt condensation product of benzaldehyde with one equivalent of acetone.
- Dibenzalacetone from two equivalents of benzaldehydePredict the double Claisen–Schmidt product when acetone reacts with two equivalents of benzaldehyde.
- Crossed aldol: isobutyraldehyde + formaldehydePredict the product when formaldehyde serves as the only acceptor in a crossed aldol.
- Henry nitroaldol: nitromethane + benzaldehydePredict the β-nitro alcohol from a Henry reaction.
- Intramolecular aldol of hexane-2,5-dione: productPredict the enone formed by intramolecular aldol condensation of a 1,4-diketone.
- Knoevenagel: benzaldehyde + diethyl malonatePredict the product of a Knoevenagel condensation with a malonate ester.
- Mannich reaction: acetone + formaldehyde + dimethylaminePredict the β-amino ketone of a three-component Mannich reaction.
- Self-aldol addition of acetonePredict the self-aldol product of a symmetrical ketone.
- Self-aldol of cyclohexanonePredict the self-aldol addition product of a cyclic ketone.
- Self-aldol addition of propanalPredict the β-hydroxy aldehyde from a cold self-aldol of propanal.
Classify 5
- Aldol addition — locate the beta-hydroxy groupRecognize beta-hydroxy connectivity relative to the retained carbonyl.
- Spot the aldol productRecognize the β-hydroxy carbonyl pattern of an aldol addition product.
- Mechanism of base-promoted aldol dehydrationClassify the elimination step of a base-promoted aldol condensation as E1cB and say why it is not E2 or E1.
- Which aldehydes can be aldol enolate donors?Decide whether benzaldehyde, formaldehyde and 2,2-dimethylpropanal can serve as enolate donors in a crossed aldol.
- Syn and anti aldol products definedDefine the syn/anti descriptors for aldol diastereomers.
Compare 1
- Aldol donor selection — benzaldehyde vs propanalExplain why an aromatic aldehyde without alpha H serves as acceptor but not a conventional enolate donor.
Calculate 6
- Intramolecular aldol addition — count the dialdehyde ringDetermine ring size from a specified donor and acceptor in a tethered dicarbonyl.
- Aldol addition — count propanal-product stereoisomersCount possible configurations when aldol addition creates two distinct stereogenic carbons.
- Equilibrium aldol product from KCalculate the equilibrium concentration of an aldol addition product from K.
- Crossed aldol of acetaldehyde and propanal: product countCount the constitutionally different aldol addition products of a crossed aldol between two enolizable aldehydes.
- Intramolecular aldol of heptane-2,6-dione: ring sizeCalculate the ring size formed in an intramolecular aldol of a 1,5-diketone.
- Stereoisomers from the propanal self-aldolCount new stereocentres and stereoisomers of an aldol addition product.
Find the error 2
- Crossed aldol selectivity — competing donors and acceptorsExplain why two enolizable partners can generate multiple constitutional products.
- Intramolecular aldol of octane-2,7-dione: choose the donorDecide which enolate of a diketone gives the favored ring size in an intramolecular aldol.
Interpret the evidence 2
- The bond an aldol formsIdentify the new C–C bond in an aldol addition.
- Which step makes the acetone aldol condensation goIdentify the step that drives an aldol condensation to completion.
Work backward 4
- Retro-aldol reaction — recover acetone and benzaldehydeIdentify the bond cleavage and carbonyl partners of a beta-hydroxy ketone.
- Retro-aldol of diacetone alcoholIdentify the carbonyl starting materials of a β-hydroxy ketone by retro-aldol disconnection.
- Retrosynthesis of 3-methylcyclohex-2-en-1-oneIdentify the diketone that cyclizes to a cyclic enone.
- Retrosynthesis of benzalacetone (4-phenylbut-3-en-2-one)Find the carbonyl partners of an α,β-unsaturated ketone by aldol disconnection.
Plan a synthesis 5
- Aldol addition vs condensation — preserve the requested endpointDistinguish conditions favoring isolated addition from a dehydration endpoint.
- Stopping at addition or going to the enoneChoose conditions that favor aldol addition versus condensation.
- Directed aldol: cyclohexanone enolate + benzaldehydeChoose the order of addition that gives a single crossed aldol product.
- Synthesis of butane-1,3-diol by aldolPlan a two-step aldol route to a 1,3-diol.
- Synthesis of 4-phenylbutan-2-one by aldolPlan a chain extension to a saturated ketone through an aldol condensation.
Explain why 5
- How much base an aldol needsExplain why aldol addition needs only catalytic base.
- Why aldol dehydration is easyExplain why β-hydroxy carbonyls dehydrate readily under base.
- Intramolecular aldol: why a 4-membered ring does not formExplain why intramolecular aldols give five- and six-membered rings.
- Why the acetone self-aldol is unfavorableExplain why aldol additions of ketones lie toward the starting materials.
- When a β-hydroxy ketone undergoes retro-aldolExplain the conditions under which an aldol addition runs in reverse.
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