„Azomethin-Ylide“ – Versionsunterschied
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[[File:Azomethine ylide.png|thumb|Azomethine ylide]] |
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'''Azomethine ylides''' are nitrogen-based [[1,3-dipole]]s. They are used in [[1,3-dipolar cycloaddition]] reactions to form 5-membered [[heterocycle]]s, including [[pyrrolidine]]s and [[pyrroline]]s.<ref name = coldham /><ref>{{cite journal|last=Padwa|first=Albert|coauthors=Pearson, William H.; Harwood, L. M.; Vickers, R. J.|title=Chapter 3. Azomethine Ylides|journal=Synthetic Applications of 1,3-Dipolar Cycloaddition Chemistry Toward Heterocycles and Natural Products|year=2003|volume=59|doi=10.1002/0471221902.ch3|url=http://onlinelibrary.wiley.com/doi/10.1002/0471221902.ch3/}}</ref><ref>{{cite journal|last=Adrio|first=Javier|coauthors=Carretero, Juan C.|title=Novel dipolarophiles and dipoles in the metal-catalyzed enantioselective 1,3-dipolar cycloaddition of azomethine ylides|journal=Chemical Communications|year=2011|volume=47|issue=24|page=6784-6794|doi=10.1039/c1cc10779h}}</ref> These reactions are highly [[stereoselectivity|stereo]]- and [[regioselective]], and have the potential to form four new contiguous stereocenters. Azomethine [[ylides]] thus have high utility in total synthesis, and formation of chiral ligands and pharmaceuticals. Azomethine ylides can be generated from many sources, including aziridines, imines, and iminiums. They are often generated ''in situ'', and reacted with dipolarophiles. |
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== Structure == |
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The [[resonance structure]] below shows the [[1,3-dipole]] contribution, in which the two carbon atoms adjacent to the nitrogen have a negative or positive charge. The most common representation is that in which the nitrogen is positively charged, and the negative charge is shared between the two carbons atoms. The relative contributions of the different resonance structures depend on the substituents on the atoms. The carbon containing [[Polar effect|electron-withdrawing]] substituents will contain a more partial negative charge, due to the ability of the nearby electron-withdrawing group to stabilize the negative charge. |
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[[File:Azomethine ylide resonance.png|center|Resonance structures]] |
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Three different ylide shapes are possible, each leading to different stereochemistry in the products of [[1,3-dipolar cycloaddition]] reactions. W-shaped, U-shaped, and S-shaped ylides are possible.<ref name=coldham>{{cite journal|last=Coldham|first=Iain|coauthors=Hufton, Richard|title=Intramolecular Dipolar Cycloaddition Reactions of Azomethine Ylides|journal=Chemical Reviews|year=2005|volume=105|page=2765–2809|doi=10.1021/cr040004c|issue=7}}</ref> The W- and U-shaped ylides, in which the R substituents are on the same side, result in syn cycloaddition products, whereas S-shaped ylides result in anti products. In the examples below, the location of the R<sup>3</sup> substituent depends on its steric and electronic nature (see [[1,3-Dipolar cycloaddition#Regioselectivity|regioselectivity of 1,3 dipolar cycloadditions]]). The stereochemistry of R<sup>1</sup> and R<sup>2</sup> in the cycloaddition product are derived from the dipole. The stereochemistry of R3 is derived from the dipolarophile—-if the dipolarophile is more than mono-substituted (and [[prochiral]]), up to four new stereocenters can result in the product. |
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[[File:Azomethine ylide shapes.png|400px|center|Azomethine ylide shapes]] |
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== Generation == |
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=== From aziridines === |
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Azomethine ylides can be generated from ring opening of [[aziridines]].<ref>{{cite journal|last=Dauban|first=Philippe|coauthors=Malik Guillaume|title=A Masked 1,3-Dipole Revealed from Aziridines|journal=Angewandte Chemie International Edition|year=2009|volume=48|issue=48|page=9026–9029|doi=10.1002/anie.200904941|url=http://onlinelibrary.wiley.com/doi/10.1002/anie.200904941/abstract}}</ref> In accordance with the [[Woodward-Hoffmann rules]], the thermal 4-electron ring opening proceeds via a [[Conrotatory and disrotatory|conrotatory] process, whereas the photochemical reaction is disrotatory. |
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[[File:Aziridine opening.png|center|250px|Ring opening of aziridine to form azomethine ylide.]] |
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In this ring opening reaction, there is an issue of [[torquoselectivity]]. Electronegative substituents prefer to rotate outwards, to the same side as the R substituent on the nitrogen, whereas electropositive substituents prefer to rotate inwards.<ref>{{cite journal|last=Banks|first=Harold D.|title=Torquoselectivity Studies in the Generation of Azomethine Ylides from Substituted Aziridines|journal=Journal of Organic Chemistry|year=2010|volume=75|issue=8|page=2510–2517|doi=10.1021/jo902600y}}</ref> |
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Note that with aziridines, ring opening can result in [[aziridine#1,3-dipole formation|a different 1,3-dipole]], in which a C-N bond (rather than the C-C bond) breaks.<ref>{{cite journal|last=Cardoso|first=Ana, L.|coauthors=Pinho e Melo, Teresa M. V. D.|title=Aziridines in Formal [3+2] Cycloadditions: Synthesis of Five-Membered Heterocycles|journal=European Journal of Organic Chemistry|year=2012|issue=33|page=6479-6501|doi=10.1002/ejoc.201200406|url=http://onlinelibrary.wiley.com/doi/10.1002/ejoc.201200406/}}</ref> |
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=== By deprotonation of iminium === |
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[[File:Deprotonation of iminium.png|center|400px|Deprotonation of iminium to form azomethine ylide.]] |
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An [[iminium]] ion, such as the one above, can be formed by condensation of an aldehyde with a secondary amine. A possible disadvantage of using this method is that the ester ends up in the cycloaddition product. An alternative is to use a carboxylic acid, which can easily be removed during the cycloaddition process by decarboxylation. |
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=== From imines === |
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==== By N-Metallation ==== |
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[[File:Azomethine ylide from imine.png|350px|center|Formation of azomethine ylides by N-metallation.]] |
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=== From münchnones === |
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Ylides can be formed from [[münchnone]]s, which are [[mesoionic]] heteocycles, and act as cyclic azomethine ylides. |
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[[File:Azomethine ylide from munchnone.png|500px|center|Formation of azomethine ylide from munchnone.]] |
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== 1,3-dipolar cycloaddtion reactions == |
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[[File:Azomethine ylide cycloaddition.png|center|400px|General cycloaddition reaction of azomethine ylide with alkene.]] |
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As with other cycloaddition reactions of a 1,3-dipolar with a π-system, [[1,3-dipolar cycloaddition]] using an azomethine ylide is a 6-electron process. According to the [[Woodward-Hoffman rules]], this addition is [[suprafacial]] with respect to both the dipole and [[1,3-Dipolar cycloaddition#Dipolarophile|dipolarophile]]. The reaction is generally viewed as [[Concerted reaction|concerted]], in which the two carbon-carbon bonds are being formed at the same time. However, depending on the nature of the dipole and dipolarophile, diradical or zwitterionic intermediates are possible.<ref>{{cite journal|last=Li|first=Yi|coauthors=Houk, Kendall N.; Gonzalez, Javier|title=Pericyclic Reaction Transition States|journal=ACC. Chem. Res.|year=1995|volume=20|issue=2|page=81-90|doi=10.1021/ar00050a004|url=http://pubs.acs.org/doi/pdf/10.1021/ar00050a004}}</ref> The endo product is generally favored, as in the isoelectronic [[Diels-Alder reaction]]. In these reactions, the azomethine ylide is typically viewed as the [[HOMO]], and the electron-deficient dipolarophile as the LUMO, although cycloaddition reactions with unactivated π-systems are known to occur. |
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1,3-dipolar cycloaddition reactions of azomethine ylides commonly use [[alkene]]s or [[alkyne]]s as dipolarophiles, to form [[pyrrolidines]] or [[pyrrolines]], respectively. A reaction of an azomethine ylide with an alkene is shown above, and results in a pyrrolidine. Whiel dipolarophiles are typically [[Carbonyl#α,β-Unsaturated carbonyl compounds|α,β-unsaturated carbonyl]] compounds, there have been many recent advances in developing new types of dipolarophiles.<ref>{{cite journal|last=Adrio|first=Javier|coauthors=Carreter, Juan C.|title=Novel dipolarophiles and dipoles in the metal-catalyzed enantioselective 1,3-dipolar cycloaddition of azomethine ylides|journal=Chem. Commun.|year=2011|volume=47|page=6784–6794|doi=10.1039/c1cc10779h}}</ref> |
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When the dipole and dipolarophile are part of the same molecule, an [[intramolecular]] cyclization reaction can lead to a polycyclic product of considerable complexity.<ref name=coldham /> If the dipolarophile is tethered to a carbon of the dipole, a fused bicycle is formed. If it is tethered to the nitrogen, a bridged structure results. The intramolecular nature of the reaction can also be useful in that regioselectivity is often constrained. Another advantage to intramolecular reactions is that the dipolarophile need not be electron-deficient—-examples of cyclization reactions with electron-rich, alkyl-substituted dipolarophiles have been reported. |
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====Stereoselectivity of cycloadditions==== |
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Unlike most 1,3-dipolar cycloaddition reactions, in which the stereochemistry of the dipole is lost or non-existent, azomethine ylides are able to retain their stereochemistry. This is generally done by ring opening of an aziridine, and subsequent trapping by a dipolarophile before the stereochemistry can scramble. |
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Like other 1,3-dipolar cycloaddition reactions, azomethine ylide cycloadditions can form endo or exo products. This selectivity can be highly tuned using metal catalysis.<ref>{{cite journal|last=Zhang|first=Xumu|coauthors=Malati Raghunath, Wenzhong Gao|title=Cu(I)-Catalyzed Highly Exo-selective and Enantioselective [3 + 2] Cycloaddition of Azomethine Ylides with Acrylates|journal=Organic Letters|year=2005|volume=7|issue=19|page=4241-4244|doi=10.1021/ol0516925|url=http://pubs.acs.org/doi/abs/10.1021/ol0516925}}</ref> <ref>{{cite journal|last=Fukuzawa|first=Shin-ichi|coauthors=Ichiro Oura, Kenta Shimizu, Kenichi Ogata|title=Highly Endo-Selective and Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylide with α-Enones Catalyzed by a Silver(I)/ThioClickFerrophos Complex|journal=Organic Letters|year=2010|volume=12|issue=8|page=1752-1755|doi=10.1021/ol100336q|url=http://pubs.acs.org/doi/abs/10.1021/ol100336q}}</ref> |
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====Enantioselective synthesis==== |
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[[Enantioselective synthesis|Enantioselective]] cycloaddition of azomethine ylides using chiral catalysts was first described in a seminal work by Allway and Grigg in 1991.<ref>{{cite journal|last=Allway|first=Philip|coauthors=Grigg, Ronald|title=Chiral cobalt(II) and manganese(II) catalysts for the 1,3-dipolar cycloaddition reactions of azomethine ylides derived from arylidene imines of glycine|journal=Tetrahedron Letters|year=1991|volume=32|issue=41|page=5817-20|doi=10.1016/S0040-4039(00)93563-9}}</ref> This powerful method was later further developed by Jørgensen and Zhang. These reactions generally use Zn, Ag, Cu, Ni, and Ca complexes. |
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Using chiral [[Metal phosphine complex|phosphine catalysts]], enantiomerically pure spiroindolinones can be synthesized. The method described by Gong, et al. leads to an unexpected regiochemical outcome that does not follow electronic effects. This is attributed to favorable [[pi stacking]] with the catalyst.<ref>{{cite journal|last=Gong|first=Liu-Zhu|coauthors=Chen, Xiao-Hua; Wei, Qiang; Luo, Shi-Wei; Xiao, Han|title=Organocatalytic Synthesis of Spiro[pyrrolidin-3,3′-oxindoles] with High Enantiopurity and Structural Diversity|journal=J. Am. Chem. Soc.|year=2009|volume=131|issue=38|page=13819–13825|doi=10.1021/ja905302f|url=http://pubs.acs.org/doi/abs/10.1021/ja905302f}}</ref> |
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== Other reactions == |
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=== Electrocyclizations === |
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[[Conjugated system|Conjugated]] azomethine ylides are capable of 1,5- and 1,7-[[electrocyclization]]s.<ref>{{cite journal |
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|last=Nedolya |
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|first=N. A. |
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|coauthors=Trofimov, B. A. |
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|title=[1,7]-Electrocyclization reactions in the synthesis of azepine derivatives |
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|journal=Chemistry of Heterocyclic Compounds |
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|year=2013 |
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|volume=49 |
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|issue=1 |
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|page=152-176 |
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|doi=10.1007/s10593-013-1236-y}}</ref> |
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An example of a 1,7-electrocyclization of a diphenylethenyl-substituted azomethine ylide is shown below. This reaction proceeds in good yield, depending on sterics and on the extent of the electron-withdrawing ability of the substituent on the N of the ylide.<ref>{{cite journal|last=Nyerges|first=Miklós|title=1,7-Electrocyclization reactions of stabilized α,β:γ,δ-unsaturated azomethine ylides|journal=Tetrahedron|year=2006|volume=16|issue=24|page=5725–5735|doi=10.1016/j.tet.2006.03.088|url=http://www.sciencedirect.com/science/article/pii/S0040402006005072#}}</ref> |
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[[File:Ylide 1,7 electrocyclization.png|center|1000px|1,7 electrocyclization of azomethine ylide]] |
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The compounds resulting from this type of electrocyclization have been used as dienes in Diels-Alder reactions to attach compounds to [[fullerene]]s. <ref>{{cite journal|last=Nierengarten|first=Jean-François|title=An unexpected Diels–Alder reaction on the fullerene core rather than an expected 1,3-dipolar cycloaddition|journal=Chem. Commun.|year=2002|issue=7|page=712-713|doi=10.1039/B201122K|url=http://pubs.rsc.org/en/content/articlelanding/2002/cc/b201122k#}}</ref> |
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== Use in synthesis == |
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=== Total synthesis of martinellic acid === |
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[[File:Martinellic acid synthesis.jpg|center|Step of martinellic acid synthesis using azomethine ylide.]] |
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A cycloaddition of an azomethine ylide with an unactivated alkene was used in total synthesis of martinellic acid. The cycloaddition step formed two rings, including a pyrrolidine, and two stereocenters.<ref>{{cite journal|last=Snider|first=BB|coauthors=Ahn Y, O'Hare SM|title=Total synthesis of (+/-)-martinellic acid|journal=Organic Letters|year=2001|volume=3|issue=26|page=4217–20|doi=10.1021/ol016884o|url=http://pubs.acs.org/doi/abs/10.1021/ol016884o}}</ref> |
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=== Total synthesis of spirotryprostatin A === |
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[[File:Application of azomethine ylide in the synthesis of spirotryprostatin.tif|center|1000px|Step of spirotryprostatin synthesis using azomethine ylide.]] |
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In the synthesis of spirotryprostatin A, an azomethine ylide is formed from condensation of an amine with an aldehyde. The ylide then reacts with an electron-deficient alkene on an indolinone, resulting in formation of a [[spirocycle|spirocyclic]] pyrrolidine and four contiguous stereocenters. <ref>{{cite journal|last=Williams|first=Robert|title=Concise, Asymmetric Total Synthesis of Spirotryprostatin A|journal=Organic Letters|year=2003|volume=5|issue=17|page=3135-37|doi=10.1021/ol0351910|url=http://pubs.acs.org/doi/abs/10.1021/ol0351910}}</ref> |
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=== Synthesis of benzodiazepinones === |
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[[File:Benzodiazepinones from azomethine ylides.png|center|600px|Synthesis of benzodiazepinones from azomethine ylide cyclizations]] |
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Cyclization of an azomethine ylide with a carbonyl affords a spirocyclic [[oxazolidine]], which loses CO<sub>2</sub> to form a 7-membered ring. These high-utility [[decarboxilation|decarboxilative]] multi-step reactions are common in azomethine ylide chemistry. <ref>{{cite journal|last=Ryan|first=John H|title=1,3-Dipolar cycloaddition-decarboxylation reactions of an azomethine ylide with isatoic anhydrides: formation of novel benzodiazepinones|journal=Organic Letters|year=2011|volume=13|issue=3|page=486-489|doi=10.1021/ol102824k|url=http://pubs.acs.org/doi/pdf/10.1021/ol102824k}}</ref> |
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== References == |
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{{reflist}} |
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[[:Category:Organic chemistry]] |
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Version vom 2. Dezember 2013, 02:56 Uhr
Weiterleitung nach:
Azomethine ylides are nitrogen-based 1,3-dipoles. They are used in 1,3-dipolar cycloaddition reactions to form 5-membered heterocycles, including pyrrolidines and pyrrolines.[1][2][3] These reactions are highly stereo- and regioselective, and have the potential to form four new contiguous stereocenters. Azomethine ylides thus have high utility in total synthesis, and formation of chiral ligands and pharmaceuticals. Azomethine ylides can be generated from many sources, including aziridines, imines, and iminiums. They are often generated in situ, and reacted with dipolarophiles.
Structure
The resonance structure below shows the 1,3-dipole contribution, in which the two carbon atoms adjacent to the nitrogen have a negative or positive charge. The most common representation is that in which the nitrogen is positively charged, and the negative charge is shared between the two carbons atoms. The relative contributions of the different resonance structures depend on the substituents on the atoms. The carbon containing electron-withdrawing substituents will contain a more partial negative charge, due to the ability of the nearby electron-withdrawing group to stabilize the negative charge.
Three different ylide shapes are possible, each leading to different stereochemistry in the products of 1,3-dipolar cycloaddition reactions. W-shaped, U-shaped, and S-shaped ylides are possible.[1] The W- and U-shaped ylides, in which the R substituents are on the same side, result in syn cycloaddition products, whereas S-shaped ylides result in anti products. In the examples below, the location of the R3 substituent depends on its steric and electronic nature (see regioselectivity of 1,3 dipolar cycloadditions). The stereochemistry of R1 and R2 in the cycloaddition product are derived from the dipole. The stereochemistry of R3 is derived from the dipolarophile—-if the dipolarophile is more than mono-substituted (and prochiral), up to four new stereocenters can result in the product.
Generation
From aziridines
Azomethine ylides can be generated from ring opening of aziridines.[4] In accordance with the Woodward-Hoffmann rules, the thermal 4-electron ring opening proceeds via a [[Conrotatory and disrotatory|conrotatory] process, whereas the photochemical reaction is disrotatory.
In this ring opening reaction, there is an issue of torquoselectivity. Electronegative substituents prefer to rotate outwards, to the same side as the R substituent on the nitrogen, whereas electropositive substituents prefer to rotate inwards.[5]
Note that with aziridines, ring opening can result in a different 1,3-dipole, in which a C-N bond (rather than the C-C bond) breaks.[6]
By deprotonation of iminium
An iminium ion, such as the one above, can be formed by condensation of an aldehyde with a secondary amine. A possible disadvantage of using this method is that the ester ends up in the cycloaddition product. An alternative is to use a carboxylic acid, which can easily be removed during the cycloaddition process by decarboxylation.
From imines
By N-Metallation
From münchnones
Ylides can be formed from münchnones, which are mesoionic heteocycles, and act as cyclic azomethine ylides.
1,3-dipolar cycloaddtion reactions
As with other cycloaddition reactions of a 1,3-dipolar with a π-system, 1,3-dipolar cycloaddition using an azomethine ylide is a 6-electron process. According to the Woodward-Hoffman rules, this addition is suprafacial with respect to both the dipole and dipolarophile. The reaction is generally viewed as concerted, in which the two carbon-carbon bonds are being formed at the same time. However, depending on the nature of the dipole and dipolarophile, diradical or zwitterionic intermediates are possible.[7] The endo product is generally favored, as in the isoelectronic Diels-Alder reaction. In these reactions, the azomethine ylide is typically viewed as the HOMO, and the electron-deficient dipolarophile as the LUMO, although cycloaddition reactions with unactivated π-systems are known to occur.
1,3-dipolar cycloaddition reactions of azomethine ylides commonly use alkenes or alkynes as dipolarophiles, to form pyrrolidines or pyrrolines, respectively. A reaction of an azomethine ylide with an alkene is shown above, and results in a pyrrolidine. Whiel dipolarophiles are typically α,β-unsaturated carbonyl compounds, there have been many recent advances in developing new types of dipolarophiles.[8]
When the dipole and dipolarophile are part of the same molecule, an intramolecular cyclization reaction can lead to a polycyclic product of considerable complexity.[1] If the dipolarophile is tethered to a carbon of the dipole, a fused bicycle is formed. If it is tethered to the nitrogen, a bridged structure results. The intramolecular nature of the reaction can also be useful in that regioselectivity is often constrained. Another advantage to intramolecular reactions is that the dipolarophile need not be electron-deficient—-examples of cyclization reactions with electron-rich, alkyl-substituted dipolarophiles have been reported.
Stereoselectivity of cycloadditions
Unlike most 1,3-dipolar cycloaddition reactions, in which the stereochemistry of the dipole is lost or non-existent, azomethine ylides are able to retain their stereochemistry. This is generally done by ring opening of an aziridine, and subsequent trapping by a dipolarophile before the stereochemistry can scramble.
Like other 1,3-dipolar cycloaddition reactions, azomethine ylide cycloadditions can form endo or exo products. This selectivity can be highly tuned using metal catalysis.[9] [10]
Enantioselective synthesis
Enantioselective cycloaddition of azomethine ylides using chiral catalysts was first described in a seminal work by Allway and Grigg in 1991.[11] This powerful method was later further developed by Jørgensen and Zhang. These reactions generally use Zn, Ag, Cu, Ni, and Ca complexes. Using chiral phosphine catalysts, enantiomerically pure spiroindolinones can be synthesized. The method described by Gong, et al. leads to an unexpected regiochemical outcome that does not follow electronic effects. This is attributed to favorable pi stacking with the catalyst.[12]
Other reactions
Electrocyclizations
Conjugated azomethine ylides are capable of 1,5- and 1,7-electrocyclizations.[13] An example of a 1,7-electrocyclization of a diphenylethenyl-substituted azomethine ylide is shown below. This reaction proceeds in good yield, depending on sterics and on the extent of the electron-withdrawing ability of the substituent on the N of the ylide.[14]
The compounds resulting from this type of electrocyclization have been used as dienes in Diels-Alder reactions to attach compounds to fullerenes. [15]
Use in synthesis
Total synthesis of martinellic acid
A cycloaddition of an azomethine ylide with an unactivated alkene was used in total synthesis of martinellic acid. The cycloaddition step formed two rings, including a pyrrolidine, and two stereocenters.[16]
Total synthesis of spirotryprostatin A
In the synthesis of spirotryprostatin A, an azomethine ylide is formed from condensation of an amine with an aldehyde. The ylide then reacts with an electron-deficient alkene on an indolinone, resulting in formation of a spirocyclic pyrrolidine and four contiguous stereocenters. [17]
Synthesis of benzodiazepinones
Cyclization of an azomethine ylide with a carbonyl affords a spirocyclic oxazolidine, which loses CO2 to form a 7-membered ring. These high-utility decarboxilative multi-step reactions are common in azomethine ylide chemistry. [18]
References
- ↑ a b c Iain Coldham, Hufton, Richard: Intramolecular Dipolar Cycloaddition Reactions of Azomethine Ylides. In: Chemical Reviews. 105. Jahrgang, Nr. 7, 2005, S. 2765–2809, doi:10.1021/cr040004c.
- ↑ Albert Padwa, Pearson, William H.; Harwood, L. M.; Vickers, R. J.: Chapter 3. Azomethine Ylides. In: Synthetic Applications of 1,3-Dipolar Cycloaddition Chemistry Toward Heterocycles and Natural Products. 59. Jahrgang, 2003, doi:10.1002/0471221902.ch3 (wiley.com).
- ↑ Javier Adrio, Carretero, Juan C.: Novel dipolarophiles and dipoles in the metal-catalyzed enantioselective 1,3-dipolar cycloaddition of azomethine ylides. In: Chemical Communications. 47. Jahrgang, Nr. 24, 2011, S. 6784–6794, doi:10.1039/c1cc10779h.
- ↑ Philippe Dauban, Malik Guillaume: A Masked 1,3-Dipole Revealed from Aziridines. In: Angewandte Chemie International Edition. 48. Jahrgang, Nr. 48, 2009, S. 9026–9029, doi:10.1002/anie.200904941 (wiley.com).
- ↑ Harold D. Banks: Torquoselectivity Studies in the Generation of Azomethine Ylides from Substituted Aziridines. In: Journal of Organic Chemistry. 75. Jahrgang, Nr. 8, 2010, S. 2510–2517, doi:10.1021/jo902600y.
- ↑ Ana, L. Cardoso, Pinho e Melo, Teresa M. V. D.: Aziridines in Formal [3+2] Cycloadditions: Synthesis of Five-Membered Heterocycles. In: European Journal of Organic Chemistry. Nr. 33, 2012, S. 6479–6501, doi:10.1002/ejoc.201200406 (wiley.com).
- ↑ Yi Li, Houk, Kendall N.; Gonzalez, Javier: Pericyclic Reaction Transition States. In: ACC. Chem. Res. 20. Jahrgang, Nr. 2, 1995, S. 81–90, doi:10.1021/ar00050a004 (acs.org [PDF]).
- ↑ Javier Adrio, Carreter, Juan C.: Novel dipolarophiles and dipoles in the metal-catalyzed enantioselective 1,3-dipolar cycloaddition of azomethine ylides. In: Chem. Commun. 47. Jahrgang, 2011, S. 6784–6794, doi:10.1039/c1cc10779h.
- ↑ Xumu Zhang, Malati Raghunath, Wenzhong Gao: Cu(I)-Catalyzed Highly Exo-selective and Enantioselective [3 + 2] Cycloaddition of Azomethine Ylides with Acrylates. In: Organic Letters. 7. Jahrgang, Nr. 19, 2005, S. 4241–4244, doi:10.1021/ol0516925 (acs.org).
- ↑ Shin-ichi Fukuzawa, Ichiro Oura, Kenta Shimizu, Kenichi Ogata: Highly Endo-Selective and Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylide with α-Enones Catalyzed by a Silver(I)/ThioClickFerrophos Complex. In: Organic Letters. 12. Jahrgang, Nr. 8, 2010, S. 1752–1755, doi:10.1021/ol100336q (acs.org).
- ↑ Philip Allway, Grigg, Ronald: Chiral cobalt(II) and manganese(II) catalysts for the 1,3-dipolar cycloaddition reactions of azomethine ylides derived from arylidene imines of glycine. In: Tetrahedron Letters. 32. Jahrgang, Nr. 41, 1991, S. 5817-20, doi:10.1016/S0040-4039(00)93563-9.
- ↑ Liu-Zhu Gong, Chen, Xiao-Hua; Wei, Qiang; Luo, Shi-Wei; Xiao, Han: Organocatalytic Synthesis of Spiro[pyrrolidin-3,3′-oxindoles] with High Enantiopurity and Structural Diversity. In: J. Am. Chem. Soc. 131. Jahrgang, Nr. 38, 2009, S. 13819–13825, doi:10.1021/ja905302f (acs.org).
- ↑ N. A. Nedolya, Trofimov, B. A.: [1,7]-Electrocyclization reactions in the synthesis of azepine derivatives. In: Chemistry of Heterocyclic Compounds. 49. Jahrgang, Nr. 1, 2013, S. 152–176, doi:10.1007/s10593-013-1236-y.
- ↑ Miklós Nyerges: 1,7-Electrocyclization reactions of stabilized α,β:γ,δ-unsaturated azomethine ylides. In: Tetrahedron. 16. Jahrgang, Nr. 24, 2006, S. 5725–5735, doi:10.1016/j.tet.2006.03.088 (sciencedirect.com).
- ↑ Jean-François Nierengarten: An unexpected Diels–Alder reaction on the fullerene core rather than an expected 1,3-dipolar cycloaddition. In: Chem. Commun. Nr. 7, 2002, S. 712–713, doi:10.1039/B201122K (rsc.org).
- ↑ BB Snider, Ahn Y, O'Hare SM: Total synthesis of (+/-)-martinellic acid. In: Organic Letters. 3. Jahrgang, Nr. 26, 2001, S. 4217–20, doi:10.1021/ol016884o (acs.org).
- ↑ Robert Williams: Concise, Asymmetric Total Synthesis of Spirotryprostatin A. In: Organic Letters. 5. Jahrgang, Nr. 17, 2003, S. 3135-37, doi:10.1021/ol0351910 (acs.org).
- ↑ John H Ryan: 1,3-Dipolar cycloaddition-decarboxylation reactions of an azomethine ylide with isatoic anhydrides: formation of novel benzodiazepinones. In: Organic Letters. 13. Jahrgang, Nr. 3, 2011, S. 486–489, doi:10.1021/ol102824k (acs.org [PDF]).