Organic Chemistry 2 · Functional-group transformations
Sigmatropic shifts, cycloadditions and electrocyclic reactions: practice problems
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- Claisen rearrangement of allyl phenyl ether
- Claisen rearrangement of allyl vinyl ether
- Claisen rearrangement of (E)-but-2-enyl vinyl ether
- Cope rearrangement of 3,4-dimethylhexa-1,5-diene
- Diels–Alder reaction of cyclopentadiene with maleic anhydride
- Diels–Alder reaction of isoprene with methyl acrylate
- Diels–Alder reaction of 1-methoxybuta-1,3-diene with acrolein
- Electrocyclic ring opening of 3,4-dimethylcyclobutene
- 6π Electrocyclic ring closure of (Z)-hexa-1,3,5-triene
Draw the mechanism 52
- Claisen rearrangement of allyl phenyl etherDraw the [3,3] shift of allyl phenyl ether to the ortho dienone and the two proton transfers that restore the aromatic ring in 2-allylphenol.
- Claisen rearrangement of allyl vinyl etherDraw the three arrows of the [3,3]-sigmatropic Claisen rearrangement that converts allyl vinyl ether into pent-4-enal.
- Claisen rearrangement of (E)-but-2-enyl vinyl etherDraw the Claisen rearrangement of (E)-but-2-en-1-yl vinyl ether and show that the new C–C bond forms at the methyl-bearing allyl carbon, giving 3-methylpent-4-enal.
- Cope rearrangement of 3,4-dimethylhexa-1,5-dieneDraw the three arrows of the Cope rearrangement of 3,4-dimethylhexa-1,5-diene and the octa-2,6-diene it gives.
- Diels–Alder reaction of cyclopentadiene with maleic anhydrideDraw the three arrows that join cyclopentadiene and maleic anhydride into the bicyclic anhydride adduct and decide whether the endo or exo isomer forms.
- Diels–Alder reaction of isoprene with methyl acrylateDraw the three arrows of the concerted Diels–Alder reaction between isoprene and methyl acrylate and the 'para' cyclohexene product, methyl 4-methylcyclohex-3-ene-1-carboxylate.
- Diels–Alder reaction of 1-methoxybuta-1,3-diene with acroleinDraw the concerted cycloaddition of (E)-1-methoxybuta-1,3-diene with acrolein and show why the 'ortho' adduct, 2-methoxycyclohex-3-ene-1-carbaldehyde, forms.
- Electrocyclic ring opening of 3,4-dimethylcyclobuteneDraw the two arrows that open cis-3,4-dimethylcyclobutene to hexa-2,4-diene and decide whether the opening is conrotatory or disrotatory.
- 6π Electrocyclic ring closure of (Z)-hexa-1,3,5-trieneDraw the three arrows of the thermal electrocyclic ring closure of (Z)-hexa-1,3,5-triene to cyclohexa-1,3-diene and state its rotational mode.
- Ene reaction of pent-1-ene with maleic anhydrideDraw the concerted ene reaction in which pent-1-ene transfers an allylic hydrogen to maleic anhydride while forming a C–C bond, giving 2-(pent-2-en-1-yl)succinic anhydride.
- Huisgen cycloaddition of benzyl azide with dimethyl acetylenedicarboxylateDraw benzyl azide as a 1,3-dipole with formal charges and the three arrows of its concerted cycloaddition onto dimethyl acetylenedicarboxylate, giving the triazole diester.
- Nitrone cycloaddition of N-methyl-C-phenylnitrone with methyl acrylateDraw the concerted 1,3-dipolar cycloaddition of N-methyl-C-phenylnitrone with methyl acrylate and place the ester on the carbon bonded to the ring oxygen.
- Anionic oxy-Cope rearrangement of hexa-1,5-dien-3-olDraw the deprotonation of hexa-1,5-dien-3-ol by hydride, the anionic [3,3] shift to an enolate, and the protonation that gives hex-5-enal.
- Ozonolysis of 2-methylbut-2-ene with dimethyl sulfide workupDraw the Criegee mechanism for ozonolysis of 2-methylbut-2-ene — primary ozonide, carbonyl oxide, ozonide — and its reduction by dimethyl sulfide to acetone and acetaldehyde.
- Cationic 2-aza-Cope rearrangement of a homoallyl iminiumDraw the three arrows of the cationic 2-aza-Cope rearrangement of the homoallylic N-methyleneiminium ion and explain which side the equilibrium favours.
- Cheletropic addition of sulfur dioxide to buta-1,3-dieneDraw the three arrows of the cheletropic addition in which the sulfur atom of SO2 bonds to both ends of buta-1,3-diene, giving 3-sulfolene.
- SO2 + isoprene → 3-methyl-3-sulfoleneDraw the three arrows of the cheletropic addition of sulfur dioxide to isoprene and place the methyl group on the ring C=C of 3-methyl-3-sulfolene.
- Cheletropic SO2 extrusion from 3-sulfoleneDraw the three arrows that break 3-sulfolene into buta-1,3-diene and sulfur dioxide and explain why heating drives this extrusion.
- Claisen rearrangement of allyl cyclohex-1-enyl etherDraw the three arrows of the Claisen rearrangement of allyl cyclohex-1-enyl ether to 2-allylcyclohexan-1-one and explain why no tautomerization follows.
- Claisen rearrangement of allyl p-tolyl etherDraw the [3,3] shift of allyl p-tolyl ether to the ortho dienone and the proton transfers that give 2-allyl-4-methylphenol.
- Para-Claisen rearrangement of allyl 2,6-dimethylphenyl etherDraw the Claisen shift to the methyl-blocked ortho carbon, the Cope shift that carries the allyl group to the para carbon, and the proton transfers that give 4-allyl-2,6-dimethylphenol.
- Cope rearrangement of 3-methylhexa-1,5-dieneDraw the three arrows of the [3,3] shift that converts 3-methylhexa-1,5-diene into (E)-hepta-1,5-diene and explain the E geometry.
- Boat Cope rearrangement of cis-1,2-divinylcyclopropaneDraw the three arrows of the Cope rearrangement of cis-1,2-divinylcyclopropane and explain why it runs at room temperature to cyclohepta-1,4-diene.
- Degenerate Cope rearrangement of hexa-1,5-dieneDraw the three arrows of the [3,3] shift of hexa-1,5-diene and explain why the product is the same compound.
- 1,3-Dipolar cycloaddition of diazomethane and methyl acrylateDraw the three arrows of the concerted [3+2] cycloaddition of diazomethane to methyl acrylate that give methyl 4,5-dihydro-3H-pyrazole-3-carboxylate, and explain the regiochemistry.
- Thermal ring opening of benzocyclobutene to o-xylyleneDraw the four arrows of the 4π electrocyclic opening of benzocyclobutene on its Kekulé structure and explain why o-xylylene is formed only as a reactive intermediate.
- Thermal opening of cis-3,4-dichlorocyclobuteneDraw the two arrows that open cis-3,4-dichlorocyclobutene and use the conrotatory mode to assign E and Z in (1E,3Z)-1,4-dichlorobuta-1,3-diene.
- Photochemical ring opening of cyclohexa-1,3-dieneDraw the three arrows that open cyclohexa-1,3-diene to (Z)-hexa-1,3,5-triene under light and explain why the central alkene must be Z.
- Photochemical closure of (2E,4E)-hexa-2,4-dieneDraw the two arrows that close (2E,4E)-hexa-2,4-diene to cis-3,4-dimethylcyclobutene under light and decide which rotation mode sets the cis methyls.
- Thermal 6π closure of (2E,4Z,6Z)-octa-2,4,6-trieneDraw the three arrows of the thermal 6π closure of (2E,4Z,6Z)-octa-2,4,6-triene and use the disrotatory mode to place the methyls of trans-5,6-dimethylcyclohexa-1,3-diene.
- Photochemical 6π closure of (2E,4Z,6E)-octa-2,4,6-trieneDraw the three arrows that close (2E,4Z,6E)-octa-2,4,6-triene under light and decide whether the ring-closing termini rotate con- or disrotatorily, giving trans-5,6-dimethylcyclohexa-1,3-diene.
- Thermal 6π closure of (2E,4Z,6E)-octa-2,4,6-trieneDraw the three arrows that close (2E,4Z,6E)-octa-2,4,6-triene under heat and decide whether the ring-closing termini rotate con- or disrotatorily, giving cis-5,6-dimethylcyclohexa-1,3-diene.
- Thermal ring opening of trans-3,4-dimethylcyclobuteneDraw the two arrows that open trans-3,4-dimethylcyclobutene to (2E,4E)-hexa-2,4-diene and decide which rotation mode sets the alkene geometry.
- [1,5]-H shift of 7-methylcycloheptatriene to the 3-isomerDraw the three arrows of the suprafacial [1,5]-hydrogen shift that turns 7-methylcyclohepta-1,3,5-triene into 3-methylcyclohepta-1,3,5-triene.
- [1,7]-Hydrogen shift of previtamin D3 to vitamin D3Draw the four arrows of the thermal antarafacial [1,7]-hydrogen shift that converts previtamin D3 into vitamin D3.
- [1,5]-Hydrogen shift of 5-methylcyclopenta-1,3-dieneDraw the three arrows of the suprafacial [1,5]-hydrogen shift that converts 5-methylcyclopenta-1,3-diene into 1-methylcyclopenta-1,3-diene.
- Hetero-Diels–Alder reaction of acrolein and ethyl vinyl etherDraw the three arrows of the hetero-Diels–Alder reaction in which acrolein (as the C=C–C=O diene) adds to ethyl vinyl ether, giving 2-ethoxy-3,4-dihydro-2H-pyran.
- Ireland–Claisen rearrangement of allyl acetate to pent-4-enoic acidDraw the enolate formation, O-silylation, [3,3] shift of the silyl ketene acetal and the acidic hydrolysis that give pent-4-enoic acid from allyl acetate.
- Johnson–Claisen rearrangement of allyl alcohol to ethyl pent-4-enoateDraw the acid-catalysed exchange of allyl alcohol into triethyl orthoacetate, the loss of ethanol that gives the ketene acetal, and the [3,3] shift to ethyl pent-4-enoate.
- Dichloroketene [2+2] cycloaddition with cyclopentadieneDraw the two arrows of the thermal [2+2] cycloaddition of dichloroketene to cyclopentadiene and decide which alkene carbon bonds to the carbonyl carbon.
- Diphenylketene and ethyl vinyl ether to a cyclobutanoneDraw the zwitterion from ethyl vinyl ether and diphenylketene and the ring closure that gives 3-ethoxy-2,2-diphenylcyclobutan-1-one.
- Mislow–Evans rearrangement to but-3-en-2-olDraw the [2,3]-sigmatropic sulfoxide-to-sulfenate shift of crotyl phenyl sulfoxide and the phosphite cleavage that releases but-3-en-2-ol.
- Nazarov cyclization of 2,4-dimethylpenta-1,4-dien-3-oneDraw the protonation, the 4π conrotatory ring closure and the proton transfers that turn 2,4-dimethylpenta-1,4-dien-3-one into 2,5-dimethylcyclopent-2-en-1-one.
- Benzonitrile oxide + phenylacetylene → 3,5-diphenylisoxazoleDraw the three arrows that join benzonitrile oxide and phenylacetylene into 3,5-diphenylisoxazole and explain why the ring is aromatic as soon as it forms.
- Benzonitrile oxide and styrene to 3,5-diphenyl-2-isoxazolineDraw the three arrows of the [3+2] cycloaddition of benzonitrile oxide with styrene and place the phenyl of styrene on the carbon bonded to the ring oxygen.
- Overman rearrangement of crotyl trichloroacetimidateDraw the three arrows of the Overman rearrangement of (E)-but-2-enyl 2,2,2-trichloroacetimidate and show where the nitrogen ends up on the allylic chain.
- Oxy-Cope rearrangement of hexa-1,5-dien-3-ol to hex-5-enalDraw the [3,3] shift of hexa-1,5-dien-3-ol to an enol and the two proton transfers that tautomerise the enol to hex-5-enal.
- Paternò–Büchi reaction of benzophenone and isobutyleneDraw the net bond changes of the Paternò–Büchi reaction of benzophenone with isobutylene and explain which alkene carbon bonds to the carbonyl oxygen.
- Photochemical [2+2] cycloaddition of cyclopent-2-en-1-one and ethyleneDraw the two arrows of the photochemical [2+2] cycloaddition that joins cyclopent-2-en-1-one and ethylene into bicyclo[3.2.0]heptan-2-one.
- SPAAC of benzyl azide and cyclooctyne to a fused triazoleDraw the three arrows of the copper-free cycloaddition of benzyl azide to cyclooctyne and explain why ring strain lets it run at room temperature.
- [2,3]-Wittig rearrangement of allyl benzyl etherDraw the benzylic deprotonation of allyl benzyl ether, the [2,3]-sigmatropic shift of the carbanion and the workup that give 1-phenylbut-3-en-1-ol.
- [2,3]-Wittig rearrangement to hept-1-en-5-yn-4-olDraw the deprotonation, the concerted [2,3]-Wittig shift and the workup that turn allyl but-2-ynyl ether into hept-1-en-5-yn-4-ol.
Predict the product 15
- Endo or exo adduct from cyclopentadienePredict the stereochemical outcome of the kinetically controlled cyclopentadiene–maleic anhydride cycloaddition.
- Room-temperature isomers of 5-methylcyclopentadienePredict which isomers form when 5-methylcyclopenta-1,3-diene stands at room temperature, and name the pericyclic step responsible.
- Claisen product of allyl vinyl ether on heatingPredict the γ,δ-unsaturated carbonyl product of the aliphatic Claisen rearrangement of allyl vinyl ether.
- Claisen of allyl 2,6-dimethoxyphenyl ether: para productPredict the product and the sequence of sigmatropic shifts when allyl 2,6-dimethoxyphenyl ether, with both ortho positions blocked, is heated.
- Aromatic Claisen product of allyl phenyl etherPredict the phenol isolated after the aromatic Claisen rearrangement of allyl phenyl ether, including where the allyl group ends up.
- Cope rearrangement product of 3-methylhexa-1,5-dienePredict the constitution and alkene geometry of the [3,3] Cope product from 3-methylhexa-1,5-diene.
- Phenyl azide + but-2-yne: the Huisgen triazolePredict the 1,2,3-triazole formed when phenyl azide and but-2-yne undergo a thermal 1,3-dipolar cycloaddition.
- Thermal 4π ring openingPredict the rotation mode of a thermal 4π electrocyclic ring opening.
- Closing (2E,4Z,6E)-octa-2,4,6-trienePredict the ring-fusion stereochemistry from thermal 6π closure of (2E,4Z,6E)-octa-2,4,6-triene.
- Thermal 6π ring closurePredict the rotation mode of a thermal 6π electrocyclic ring closure.
- Photochemical 6π ring closurePredict the rotation mode of a photochemical 6π electrocyclic ring closure.
- Opening trans-3,4-dimethylcyclobutenePredict diene geometry from thermal conrotatory opening of trans-3,4-dimethylcyclobutene.
- Ene reaction of propene with maleic anhydridePredict the product of the thermal Alder ene reaction between propene and maleic anhydride and identify the hydrogen that moves.
- Oxy-Cope product of hexa-1,5-dien-3-olPredict the carbonyl compound formed when hexa-1,5-dien-3-ol undergoes a thermal oxy-Cope rearrangement followed by tautomerization.
- Photodimer of cyclopentene by [2+2] cycloadditionPredict the ring system formed when two cyclopentene molecules undergo a photochemical [2+2] cycloaddition.
Classify 6
- Thermal [4+2] versus [2+2]Classify cycloadditions as thermally allowed or forbidden from the electron count of the cyclic array.
- Three classes of pericyclic reactionClassify pericyclic reactions as cycloaddition, electrocyclic or sigmatropic from the bonds made and broken.
- Classifying ozone addition to an alkeneClassify the first step of ozonolysis, the addition of ozone to an alkene, as a pericyclic reaction type with its electron count.
- A [2+2] cycloaddition under heat and lightDecide whether a suprafacial [2+2] cycloaddition of two alkenes is allowed thermally or photochemically.
- Pericyclic steps from 7-dehydrocholesterol to vitamin D3Classify the photochemical and thermal pericyclic steps that convert 7-dehydrocholesterol into vitamin D3, with their stereochemical modes.
- Thermal [4+4] cycloaddition of two butadienesApply the Woodward–Hoffmann electron-count rule to decide whether a suprafacial–suprafacial [4+4] cycloaddition is thermally or photochemically allowed.
Compare 1
- Rank dienophiles toward cyclopentadieneRank dienophiles by the number and strength of conjugated electron-withdrawing groups.
Calculate 1
- Electrons in a Cope rearrangementCount the electrons that move in the cyclic transition state of a Cope rearrangement.
Find the error 1
- Diagnose a stereochemistry errorDiagnose a proposed Diels–Alder product that breaks the stereospecificity of suprafacial addition.
Interpret the evidence 1
- The thermal selection ruleApply the 4n+2 rule to predict which thermal all-suprafacial reactions are allowed.
Work backward 3
- Disconnect a cyclohexene anhydrideIdentify the diene and dienophile that a cyclohexene product comes from by a retro-Diels–Alder disconnection.
- Diels–Alder disconnection of a cis-cyclohexene diesterChoose the diene and dienophile whose Diels–Alder reaction gives dimethyl cis-cyclohex-4-ene-1,2-dicarboxylate with the correct relative stereochemistry.
- Claisen precursor for 4-methylhex-5-en-2-oneIdentify the allyl vinyl ether whose Claisen rearrangement gives the γ,δ-unsaturated ketone 4-methylhex-5-en-2-one, accounting for allylic transposition.
Explain why 3
- Why a bulky diene failsExplain how a diene that cannot reach the s-cis conformation fails to react.
- Why heat cracks dicyclopentadiene by retro-Diels–AlderExplain with ΔG = ΔH − TΔS why a Diels–Alder adduct such as dicyclopentadiene reverts to its diene and dienophile on strong heating.
- Why light reverses the selection ruleExplain why photochemical pericyclic reactions follow the opposite selection rule to thermal ones.
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