{"history":[],"article":{"id":"4d6c3f5e-bf31-4bff-8c54-bec333f7d717","title":"Pauson–Khand reaction","slug":"pauson-khand-reaction","content":":::summary\n:::\n\n# \nThe **Pauson–Khand (PK) reaction** is a [chemical reaction](https://bliptext.com/articles/chemical-reaction), described as a[ [ 2+2+1] ](https://bliptext.com/articles/woodward-hoffmann-rules) [cycloaddition](https://bliptext.com/articles/cycloaddition).\nIn it, an [alkyne](https://bliptext.com/articles/alkyne), an [alkene](https://bliptext.com/articles/alkene), and [carbon monoxide](https://bliptext.com/articles/carbon-monoxide) combine into a α,β-[cyclopentenone](https://bliptext.com/articles/cyclopentenone) in the presence of a [metal-carbonyl](https://bliptext.com/articles/metal-carbonyl) catalyst\n[Ihsan Ullah Khand](https://bliptext.com/articles/ihsan-ullah-khand) (1935–1980) discovered the reaction around 1970, while working as a postdoctoral associate with [Peter Ludwig Pauson](https://bliptext.com/articles/peter-pauson) (1925–2013) at the [University of Strathclyde](https://bliptext.com/articles/university-of-strathclyde) in Glasgow.\nPauson and Khand's initial findings were intermolecular in nature, but the reaction has poor selectivity.\nSome modern applications instead apply the reaction for intramolecular ends.\nThe traditional reaction requires a stoichiometric amounts of [dicobalt octacarbonyl](https://bliptext.com/articles/dicobalt-octacarbonyl), stabilized by a [carbon monoxide](https://bliptext.com/articles/carbon-monoxide) [atmosphere](https://bliptext.com/articles/reducing-atmosphere).\nCatalytic metal quantities, enhanced reactivity and yield, or [stereoinduction](https://bliptext.com/articles/asymmetric-induction) are all possible with the right [chiral auxiliaries](https://bliptext.com/articles/chiral-auxiliary), choice of [transition metal](https://bliptext.com/articles/transition-metal) (Ti, Mo, W, Fe, Co, Ni, Ru, Rh, Ir and Pd), and additives.\n# [358x358px | upload.wikimedia.org/wikipedia/commons/3/32/Overview///PKR.png]\n\n# Mechanism\nWhile the mechanism has not yet been fully elucidated, Magnus' 1985 explanation is widely accepted for both mono- and dinuclear catalysts, and was corroborated by computational studies published by Nakamura and Yamanaka in 2001.\nThe reaction starts with [dicobalt hexacarbonyl acetylene complex](https://bliptext.com/articles/dicobalt-hexacarbonyl-acetylene-complex).\nBinding of an alkene gives a [metallacyclopentene](https://bliptext.com/articles/metallacyclopentanes) complex.\nCO then [migratorily inserts](https://bliptext.com/articles/migratory-insertion) into an M-C bond.\n[Reductive elimination](https://bliptext.com/articles/reductive-elimination) delivers the [cyclopentenone](https://bliptext.com/articles/cyclopentenone).\nTypically, the dissociation of carbon monoxide from the organometallic complex is rate limiting.\n# [

1:: Alkyne coordination, insertion and ligand dissociation to form an 18-electron complex;
2:: Ligand dissociation to form a 16-electron complex;
3:: Alkene coordination to form an 18-electron complex;
4:: Alkene insertion and ligand association (synperiplanar, still 18 electrons);
5:: CO migratory insertion;
6, 7:: Reductive elimination of metal (loss of [Co2(CO)6]);
8:: CO association, to regenerate the active organometallic complex.

| upload.wikimedia.org/wikipedia/commons/2/2e/Mech///PKR.png]\n\n# Selectivity\nThe reaction works with both terminal and internal alkynes, although internal alkynes tend to give lower yields.\nThe order of reactivity for the alkene is\"(strained cyclic) > (terminal) > (disubstituted) > (trisubstituted).\"\nTetrasubstituted alkenes and alkenes with strongly [electron-withdrawing groups](https://bliptext.com/articles/electron-withdrawing-group) are unsuitable.\nWith unsymmetrical alkenes or alkynes, the reaction is rarely [regioselective](https://bliptext.com/articles/regioselective), although some patterns can be observed.\nFor mono-substituted alkenes, alkyne substituents typically direct: larger groups prefer the C2 position, and electron-withdrawing groups prefer the C3 position.\nBut the alkene itself struggles to discriminate between the C4 and C5 position, unless the C2 position is sterically congested or the alkene has a chelating heteroatom.\nThe reaction's poor selectivity is ameliorated in [intramolecular reactions](https://bliptext.com/articles/intramolecular-reaction).\nFor this reason, the intramolecular Pauson-Khand is common in total synthesis, particularly the formation of 5,5- and 6,5-membered fused [bicycles](https://bliptext.com/articles/bicyclic-molecule).\nGenerally, the reaction is highly syn-selective about the bridgehead hydrogen and substituents on the cyclopentane.\nAppropriate chiral ligands or auxiliaries can make the reaction enantioselective (see ).\n[BINAP](https://bliptext.com/articles/binap) is commonly employed.\n# [The PK reaction has poor regioselectivity with monosubstituted alkenes. Phenylacetylene and 1-octene produce at least 4 isomeric products. (\"tol\" = toluene) | upload.wikimedia.org/wikipedia/commons/7/75/Intermol///pkr.png]\n# [An electron-withdrawing group (ethyl benzoatyl) prefers the C3 position. (\"Tol\" = toluene) | upload.wikimedia.org/wikipedia/commons/1/1e/EWG///PKR.png]\n# [451x451px | upload.wikimedia.org/wikipedia/commons/7/71/General///pkr.png]\n# [474x474px | upload.wikimedia.org/wikipedia/commons/d/d7/Stereosel.///pkr.png]\n\n# Additives\nTypical Pauson-Khand conditions are elevated temperatures and pressures in aromatic hydrocarbon (benzene, toluene) or ethereal (tetrahydrofuran, 1,2-dichloroethane) solvents.\nThese harsh conditions may be attenuated with the addition of various additives.\n# [545x545px | upload.wikimedia.org/wikipedia/commons/d/dd/Cat///pkr.png]\n# [Adding silica improved this reaction rate by a factor of ≈50. | upload.wikimedia.org/wikipedia/commons/3/36/Comparison///drystate-thermal.png]\n\n## Absorbent surfaces\nAdsorbing the metallic complex onto silica or alumina can enhance the rate of decarbonylative ligand exchange as exhibited in the image below.\nThis is because the donor posits itself on a solid surface (i.e. silica).\nAdditionally using a solid support restricts conformational movement ([rotamer effect](https://bliptext.com/articles/conformational-isomerism)).\n\n## Lewis bases\nTraditional catalytic aids such as phosphine ligands make the cobalt complex too stable, but bulky phosphite ligands are operable.\nLewis basic additives, such as n-BuSMe, are also believed to accelerate the decarbonylative ligand exchange process.\nHowever, an alternative view holds that the additives make olefin insertion irreversible instead.\nSulfur compounds are typically hard to handle and smelly, but [n-dodecyl methyl sulfide](https://bliptext.com/articles/n-dodecyl-methyl-sulfide) and [tetramethylthiourea](https://bliptext.com/articles/tetramethylthiourea) do not suffer from those problems and can improve reaction performance.\n# [392x392px | upload.wikimedia.org/wikipedia/commons/3/3b/Sulfur///Additive.png]\n\n## Amine N-oxides\nThe two most common amine N-oxides are N-methylmorpholine N-oxide (NMO) and trimethylamine N-oxide (TMANO).\nIt is believed that these additives remove carbon monoxide ligands via nucleophilic attack of the N-oxide onto the CO carbonyl, oxidizing the CO into CO2, and generating an unsaturated organometallic complex.\nThis renders the first step of the mechanism irreversible, and allows for more mild conditions.\n[Hydrates](https://bliptext.com/articles/hydrate) of the aforementioned amine N-oxides have similar effect.\nN-oxide additives can also improve enantio- and diastereoselectivity, although the mechanism thereby is not clear.\nScreiber_example.png, DCM = [dichloromethane](https://bliptext.com/articles/dichloromethane))\nA step in the total synthesis of epoxydictymene: temperature and ultrasound failed to improve the d.r. for the desired diastereomer (the red hydrogen).\nBut the N-oxide additive, while lower yielding, gave a d.r. of 11:1.\n]]\n# [391x391px | upload.wikimedia.org/wikipedia/commons/6/6f/Additives.png]\n\n# Alternative catalysts\n[(Co)4(CO)12](https://bliptext.com/articles/tetracobalt-dodecacarbonyl) and [Co3(CO)9(μ3-CH)](https://bliptext.com/articles/co3-co-9-ch) also catalyze the PK reaction although Takayama et al detail a reaction catalyzed by [dicobalt octacarbonyl](https://bliptext.com/articles/dicobalt-octacarbonyl).\nOne stabilization method is to generate the catalyst in situ.\nChung reports that [Co(acac)2](https://bliptext.com/articles/tris-acetylacetonato-cobalt-iii) can serve as a [precatalyst](https://bliptext.com/articles/precatalyst), activated by [sodium borohydride](https://bliptext.com/articles/sodium-borohydride).\n# [The key step in Takayama et al 's asymmetric total synthesis of the Lycopodium alkaloid huperzine-Q: Co2(CO)8 catalyzes an enyne cyclization. The siloxane ring ensures that only a single product enantiomer forms. | upload.wikimedia.org/wikipedia/commons/6/68/Syn///ex.png]\n\n## Other metals\n[catalyst](https://bliptext.com/articles/wilkinson-s-catalyst) requires a [silver triflate](https://bliptext.com/articles/silver-triflate) co-[catalyst](https://bliptext.com/articles/wilkinson-s-catalyst) to effect the Pauson–Khand reaction:\n[Molybdenum hexacarbonyl](https://bliptext.com/articles/molybdenum-hexacarbonyl) is a carbon monoxide donor in PK-type reactions between [allenes](https://bliptext.com/articles/allene) and [alkynes](https://bliptext.com/articles/alkyne) with [dimethyl sulfoxide](https://bliptext.com/articles/dimethyl-sulfoxide) in toluene.\nTitanium, nickel, and zirconium complexes admit the reaction.\nOther metals can also be employed in these transformations.\n# [PK reaction with Wilkinson's catalyst | upload.wikimedia.org/wikipedia/commons/d/d4/Ex///1///var.png]\n\n# Substrate tolerance\nIn general allenes, support the Pauson–Khand reaction; regioselectivity is determined by the choice of metal catalyst.\n[Density functional](https://bliptext.com/articles/density-functional-theory) investigations show the variation arises from different transition state metal geometries.\nHeteroatoms are also acceptable: Mukai et al 's total synthesis of physostigmine applied the Pauson–Khand reaction to a [carbodiimide](https://bliptext.com/articles/carbodiimide).\n[Cyclobutadiene](https://bliptext.com/articles/cyclobutadiene) also lends itself to a [ 2+2+1] cycloaddition, although this reactant is too active to store in bulk.\nInstead, [ceric ammonium nitrate](https://bliptext.com/articles/ceric-ammonium-nitrate) cyclobutadiene is generated in situ from [decomplexation](https://bliptext.com/articles/decomplexation) of stable [cyclobutadiene iron tricarbonyl](https://bliptext.com/articles/cyclobutadiene-iron-tricarbonyl) with (CAN).\nAn example of a newer version is the use of the [chlorodicarbonylrhodium(I) dimer](https://bliptext.com/articles/rhodium-carbonyl-chloride), [(CO)2RhCl]2, in the synthesis of [(+)-phorbol](https://bliptext.com/articles/phorbol) by [Phil Baran](https://bliptext.com/articles/phil-s-baran).\nIn addition to using a rhodium catalyst, this synthesis features an intramolecular cyclization that results in the normal 5-membered α,β-[cyclopentenone](https://bliptext.com/articles/cyclopentenone) as well as 7-membered ring.\n# [Molybdenum catalyzes a Pauson-Khand reaction at an allene's internal double bond. Rhodium would catalyze a reaction at this substrate's terminal double-bond instead. | upload.wikimedia.org/wikipedia/commons/9/96/Allene///ex.png]\n# [708x708px | upload.wikimedia.org/wikipedia/commons/5/5c/Physostigmine///.png]\n# [Pauson Khand reaction Seigal 2005 | upload.wikimedia.org/wikipedia/commons/4/4a/Can///ex.png]\n\n## Carbon monoxide generation in situ\nThe cyclopentenone motif can be prepared from aldehydes, carboxylic acids, and formates.\nThese examples typically employ rhodium as the catalyst, as it is commonly used in [decarbonylation](https://bliptext.com/articles/decarbonylation) reactions.\nThe decarbonylation and PK reaction occur in the same reaction vessel.","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-25T21:47:13.172Z","updated_at":"2025-01-25T21:47:13.172Z","search_vector":"'khand':2 'pauson':1 'reaction':3","search_content":" \n \n\n# \nThe **Pauson–Khand (PK) reaction** is a [chemical reaction](https://bliptext.com/articles/chemical-reaction), described as a[ [ 2+2+1] ](https://bliptext.com/articles/woodward-hoffmann-rules) [cycloaddition](https://bliptext.com/articles/cycloaddition).\nIn it, an [alkyne](https://bliptext.com/articles/alkyne), an [alkene](https://bliptext.com/articles/alkene), and [carbon monoxide](https://bliptext.com/articles/carbon-monoxide) combine into a α,β-[cyclopentenone](https://bliptext.com/articles/cyclopentenone) in the presence of a [metal-carbonyl](https://bliptext.com/articles/metal-carbonyl) catalyst\n[Ihsan Ullah Khand](https://bliptext.com/articles/ihsan-ullah-khand) (1935–1980) discovered the reaction around 1970, while working as a postdoctoral associate with [Peter Ludwig Pauson](https://bliptext.com/articles/peter-pauson) (1925–2013) at the [University of Strathclyde](https://bliptext.com/articles/university-of-strathclyde) in Glasgow.\nPauson and Khand's initial findings were intermolecular in nature, but the reaction has poor selectivity.\nSome modern applications instead apply the reaction for intramolecular ends.\nThe traditional reaction requires a stoichiometric amounts of [dicobalt octacarbonyl](https://bliptext.com/articles/dicobalt-octacarbonyl), stabilized by a [carbon monoxide](https://bliptext.com/articles/carbon-monoxide) [atmosphere](https://bliptext.com/articles/reducing-atmosphere).\nCatalytic metal quantities, enhanced reactivity and yield, or [stereoinduction](https://bliptext.com/articles/asymmetric-induction) are all possible with the right [chiral auxiliaries](https://bliptext.com/articles/chiral-auxiliary), choice of [transition metal](https://bliptext.com/articles/transition-metal) (Ti, Mo, W, Fe, Co, Ni, Ru, Rh, Ir and Pd), and additives.\n# [358x358px | upload.wikimedia.org/wikipedia/commons/3/32/Overview///PKR.png]\n\n# Mechanism\nWhile the mechanism has not yet been fully elucidated, Magnus' 1985 explanation is widely accepted for both mono- and dinuclear catalysts, and was corroborated by computational studies published by Nakamura and Yamanaka in 2001.\nThe reaction starts with [dicobalt hexacarbonyl acetylene complex](https://bliptext.com/articles/dicobalt-hexacarbonyl-acetylene-complex).\nBinding of an alkene gives a [metallacyclopentene](https://bliptext.com/articles/metallacyclopentanes) complex.\nCO then [migratorily inserts](https://bliptext.com/articles/migratory-insertion) into an M-C bond.\n[Reductive elimination](https://bliptext.com/articles/reductive-elimination) delivers the [cyclopentenone](https://bliptext.com/articles/cyclopentenone).\nTypically, the dissociation of carbon monoxide from the organometallic complex is rate limiting.\n# [ \n 1: Alkyne coordination, insertion and ligand dissociation to form an 18-electron complex; \n 2: Ligand dissociation to form a 16-electron complex; \n 3: Alkene coordination to form an 18-electron complex; \n 4: Alkene insertion and ligand association (synperiplanar, still 18 electrons); \n 5: CO migratory insertion; \n 6, 7: Reductive elimination of metal (loss of [Co2(CO)6]); \n 8: CO association, to regenerate the active organometallic complex. \n | upload.wikimedia.org/wikipedia/commons/2/2e/Mech///PKR.png]\n\n# Selectivity\nThe reaction works with both terminal and internal alkynes, although internal alkynes tend to give lower yields.\nThe order of reactivity for the alkene is\"(strained cyclic) > (terminal) > (disubstituted) > (trisubstituted).\"\nTetrasubstituted alkenes and alkenes with strongly [electron-withdrawing groups](https://bliptext.com/articles/electron-withdrawing-group) are unsuitable.\nWith unsymmetrical alkenes or alkynes, the reaction is rarely [regioselective](https://bliptext.com/articles/regioselective), although some patterns can be observed.\nFor mono-substituted alkenes, alkyne substituents typically direct: larger groups prefer the C2 position, and electron-withdrawing groups prefer the C3 position.\nBut the alkene itself struggles to discriminate between the C4 and C5 position, unless the C2 position is sterically congested or the alkene has a chelating heteroatom.\nThe reaction's poor selectivity is ameliorated in [intramolecular reactions](https://bliptext.com/articles/intramolecular-reaction).\nFor this reason, the intramolecular Pauson-Khand is common in total synthesis, particularly the formation of 5,5- and 6,5-membered fused [bicycles](https://bliptext.com/articles/bicyclic-molecule).\nGenerally, the reaction is highly syn-selective about the bridgehead hydrogen and substituents on the cyclopentane.\nAppropriate chiral ligands or auxiliaries can make the reaction enantioselective (see ).\n[BINAP](https://bliptext.com/articles/binap) is commonly employed.\n# [The PK reaction has poor regioselectivity with monosubstituted alkenes. Phenylacetylene and 1-octene produce at least 4 isomeric products. (\"tol\" = toluene) | upload.wikimedia.org/wikipedia/commons/7/75/Intermol///pkr.png]\n# [An electron-withdrawing group (ethyl benzoatyl) prefers the C3 position. (\"Tol\" = toluene) | upload.wikimedia.org/wikipedia/commons/1/1e/EWG///PKR.png]\n# [451x451px | upload.wikimedia.org/wikipedia/commons/7/71/General///pkr.png]\n# [474x474px | upload.wikimedia.org/wikipedia/commons/d/d7/Stereosel.///pkr.png]\n\n# Additives\nTypical Pauson-Khand conditions are elevated temperatures and pressures in aromatic hydrocarbon (benzene, toluene) or ethereal (tetrahydrofuran, 1,2-dichloroethane) solvents.\nThese harsh conditions may be attenuated with the addition of various additives.\n# [545x545px | upload.wikimedia.org/wikipedia/commons/d/dd/Cat///pkr.png]\n# [Adding silica improved this reaction rate by a factor of ≈50. | upload.wikimedia.org/wikipedia/commons/3/36/Comparison///drystate-thermal.png]\n\n## Absorbent surfaces\nAdsorbing the metallic complex onto silica or alumina can enhance the rate of decarbonylative ligand exchange as exhibited in the image below.\nThis is because the donor posits itself on a solid surface (i.e. silica).\nAdditionally using a solid support restricts conformational movement ([rotamer effect](https://bliptext.com/articles/conformational-isomerism)).\n\n## Lewis bases\nTraditional catalytic aids such as phosphine ligands make the cobalt complex too stable, but bulky phosphite ligands are operable.\nLewis basic additives, such as n-BuSMe, are also believed to accelerate the decarbonylative ligand exchange process.\nHowever, an alternative view holds that the additives make olefin insertion irreversible instead.\nSulfur compounds are typically hard to handle and smelly, but [n-dodecyl methyl sulfide](https://bliptext.com/articles/n-dodecyl-methyl-sulfide) and [tetramethylthiourea](https://bliptext.com/articles/tetramethylthiourea) do not suffer from those problems and can improve reaction performance.\n# [392x392px | upload.wikimedia.org/wikipedia/commons/3/3b/Sulfur///Additive.png]\n\n## Amine N-oxides\nThe two most common amine N-oxides are N-methylmorpholine N-oxide (NMO) and trimethylamine N-oxide (TMANO).\nIt is believed that these additives remove carbon monoxide ligands via nucleophilic attack of the N-oxide onto the CO carbonyl, oxidizing the CO into CO2, and generating an unsaturated organometallic complex.\nThis renders the first step of the mechanism irreversible, and allows for more mild conditions.\n[Hydrates](https://bliptext.com/articles/hydrate) of the aforementioned amine N-oxides have similar effect.\nN-oxide additives can also improve enantio- and diastereoselectivity, although the mechanism thereby is not clear.\nScreiber_example.png, DCM = [dichloromethane](https://bliptext.com/articles/dichloromethane))\nA step in the total synthesis of epoxydictymene: temperature and ultrasound failed to improve the d.r. for the desired diastereomer (the red hydrogen).\nBut the N-oxide additive, while lower yielding, gave a d.r. of 11:1.\n]]\n# [391x391px | upload.wikimedia.org/wikipedia/commons/6/6f/Additives.png]\n\n# Alternative catalysts\n[(Co)4(CO)12](https://bliptext.com/articles/tetracobalt-dodecacarbonyl) and [Co3(CO)9(μ3-CH)](https://bliptext.com/articles/co3-co-9-ch) also catalyze the PK reaction although Takayama et al detail a reaction catalyzed by [dicobalt octacarbonyl](https://bliptext.com/articles/dicobalt-octacarbonyl).\nOne stabilization method is to generate the catalyst in situ.\nChung reports that [Co(acac)2](https://bliptext.com/articles/tris-acetylacetonato-cobalt-iii) can serve as a [precatalyst](https://bliptext.com/articles/precatalyst), activated by [sodium borohydride](https://bliptext.com/articles/sodium-borohydride).\n# [The key step in Takayama et al 's asymmetric total synthesis of the Lycopodium alkaloid huperzine-Q: Co2(CO)8 catalyzes an enyne cyclization. The siloxane ring ensures that only a single product enantiomer forms. | upload.wikimedia.org/wikipedia/commons/6/68/Syn///ex.png]\n\n## Other metals\n[catalyst](https://bliptext.com/articles/wilkinson-s-catalyst) requires a [silver triflate](https://bliptext.com/articles/silver-triflate) co-[catalyst](https://bliptext.com/articles/wilkinson-s-catalyst) to effect the Pauson–Khand reaction:\n[Molybdenum hexacarbonyl](https://bliptext.com/articles/molybdenum-hexacarbonyl) is a carbon monoxide donor in PK-type reactions between [allenes](https://bliptext.com/articles/allene) and [alkynes](https://bliptext.com/articles/alkyne) with [dimethyl sulfoxide](https://bliptext.com/articles/dimethyl-sulfoxide) in toluene.\nTitanium, nickel, and zirconium complexes admit the reaction.\nOther metals can also be employed in these transformations.\n# [PK reaction with Wilkinson's catalyst | upload.wikimedia.org/wikipedia/commons/d/d4/Ex///1///var.png]\n\n# Substrate tolerance\nIn general allenes, support the Pauson–Khand reaction; regioselectivity is determined by the choice of metal catalyst.\n[Density functional](https://bliptext.com/articles/density-functional-theory) investigations show the variation arises from different transition state metal geometries.\nHeteroatoms are also acceptable: Mukai et al 's total synthesis of physostigmine applied the Pauson–Khand reaction to a [carbodiimide](https://bliptext.com/articles/carbodiimide).\n[Cyclobutadiene](https://bliptext.com/articles/cyclobutadiene) also lends itself to a [ 2+2+1] cycloaddition, although this reactant is too active to store in bulk.\nInstead, [ceric ammonium nitrate](https://bliptext.com/articles/ceric-ammonium-nitrate) cyclobutadiene is generated in situ from [decomplexation](https://bliptext.com/articles/decomplexation) of stable [cyclobutadiene iron tricarbonyl](https://bliptext.com/articles/cyclobutadiene-iron-tricarbonyl) with (CAN).\nAn example of a newer version is the use of the [chlorodicarbonylrhodium(I) dimer](https://bliptext.com/articles/rhodium-carbonyl-chloride), [(CO)2RhCl]2, in the synthesis of [(+)-phorbol](https://bliptext.com/articles/phorbol) by [Phil Baran](https://bliptext.com/articles/phil-s-baran).\nIn addition to using a rhodium catalyst, this synthesis features an intramolecular cyclization that results in the normal 5-membered α,β-[cyclopentenone](https://bliptext.com/articles/cyclopentenone) as well as 7-membered ring.\n# [Molybdenum catalyzes a Pauson-Khand reaction at an allene's internal double bond. Rhodium would catalyze a reaction at this substrate's terminal double-bond instead. | upload.wikimedia.org/wikipedia/commons/9/96/Allene///ex.png]\n# [708x708px | upload.wikimedia.org/wikipedia/commons/5/5c/Physostigmine///.png]\n# [Pauson Khand reaction Seigal 2005 | upload.wikimedia.org/wikipedia/commons/4/4a/Can///ex.png]\n\n## Carbon monoxide generation in situ\nThe cyclopentenone motif can be prepared from aldehydes, carboxylic acids, and formates.\nThese examples typically employ rhodium as the catalyst, as it is commonly used in [decarbonylation](https://bliptext.com/articles/decarbonylation) reactions.\nThe decarbonylation and PK reaction occur in the same reaction vessel.","revisionCount":0},"hasMore":false,"nextCursor":null}

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