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{{merge from|Epoxidation with dioxiranes|discuss=Talk:Epoxidation with dioxiranes#Merge proposal|date=January 2024}}
{{merge from|Epoxidation with dioxiranes|discuss=Talk:Epoxidation with dioxiranes#Merge proposal|date=January 2024}}
'''Oxidation with dioxiranes''' refers to the introduction of oxygen into organic molecules through the action of a [[dioxirane]]. Dioxiranes are well known for their oxidation of alkenes to epoxides; however, they are also able to oxidize other unsaturated functionality, heteroatoms, and alkane C-H bonds.<ref>Adam, W.; Zhao, C.-G.; Jakka, K. ''[[Org. React.]]'' '''2007''', ''69'', 1. {{doi|10.1002/0471264180.or069.01}}</ref>
'''Oxidation with dioxiranes''' refers to the introduction of oxygen into organic molecules through the action of a [[dioxirane]]. Dioxiranes are well known for their oxidation of alkenes to epoxides; however, they are also able to oxidize other unsaturated functionality, heteroatoms, and alkane C-H bonds.<ref>Adam, W.; Zhao, C.-G.; Jakka, K. ''[[Org. React.]]'' '''2007''', ''69'', 1. {{doi|10.1002/0471264180.or069.01}}</ref>

'''Epoxidation with dioxiranes''' refers to the synthesis of [[epoxide]]s from [[alkene]]s using [[dioxirane]]s.<ref>Adam, W.; Saha-Moller, C.; Zhao, C.-G. ''[[Org. React.]]'' '''2003''', ''61'', 219. {{doi|10.1002/0471264180.or061.02}}</ref>

Dioxiranes are three-membered cyclic peroxides containing a weak oxygen-oxygen bond. Although they are able to effect oxidations of heteroatom functionality and even carbon-hydrogen bonds,<ref>Adam, W.; Zhao, C.-G.; Jakka, K. ''Org. React.'' '''2007''', ''69'', 1.</ref> they are most widely used as epoxidizing agents of alkenes. Dioxiranes are electrophilic oxidants that react more quickly with electron-rich than electron-poor double bonds; however, both classes of substrates can be epoxidized within a reasonable time frame. Dioxiranes may be prepared and isolated or generated ''in situ'' from ketones and potassium peroxymonosulfate ([[Oxone]]). ''In situ'' preparations may be catalytic in ketone, and if the ketone is chiral, enantioselective epoxidation takes place. The functional group compatibility of dioxiranes is limited somewhat, as side oxidations of amines and sulfides are rapid. Nonetheless, protocols for dioxirane oxidations are entirely metal free. The most common dioxiranes employed for synthesis are dimethyl dioxirane (DMD) and methyl(trifluoromethyl)dioxirane (TFD).
:[[File:DOEpoxGen.png]]

==Mechanism and stereochemistry==

The mechanism of epoxidation with dioxiranes most likely involves concerted oxygen transfer through a [[spiro compound|spiro]] transition state.<ref>Houk, K. N.; Liu, J.; DeMello, N. C.; Condroski, K. R. ''J. Am. Chem. Soc.'' '''1997''', ''119'', 10147.</ref> As oxygen transfer occurs, the plane of the oxirane is perpendicular to and bisects the plane of the alkene pi system. The configuration of the alkene is maintained in the product, ruling out long-lived radical intermediates. In addition, the spiro transition state has been used to explain the sense of selectivity in enantioselective epoxidations with chiral ketones.<ref name=Shi>Wang, Z.-X.; Tu, Y.; Frohn, M.; Zhang, J.-R.; Shi, Y. ''J. Am. Chem. Soc.'' '''1997''', ''119'', 11224.</ref>
:[[File:DOEpoxMech.png]]


Diastereoselective epoxidation may be achieved through the use of alkene starting materials with diastereotopic faces. When racemic 3-isopropylcyclohexene was subjected to DMD oxidation, the ''trans'' epoxide, which resulted from attack on the less hindered face of the double bond, was the major product.<ref>Adam, W.; Mitchell, C. M.; Saha-Möller, C. R. ''Eur. J. Org. Chem.'' '''1999''', 785.</ref>
:[[File:DOEpoxStereo1.png]]

==Scope and limitations==
Dioxiranes may either be prepared in advance or generated ''in situ'' for epoxidation reactions. In most cases, a two-phase system must be set up for ''in situ'' epoxidations, as KHSO<sub>5</sub> is not soluble in organic solvents. Thus, substrates or products sensitive to hydrolysis will not survive ''in situ'' epoxidations.<ref>Denmark, S. E.; Wu, Z. ''J. Org. Chem.'' '''1998''', ''63'', 2810.</ref> This section describes epoxidation conditions for alkenes with electron-donating or -withdrawing substituents, both of which may be epoxidized with dioxiranes in either the stoichiometric or catalytic mode.

Although dioxiranes are highly electrophilic, they epoxidize both electron-rich and electron-poor alkenes in good yield (although the latter react much more slowly). Electron-poor epoxide products also exhibit enhanced hydrolytic stability, meaning that they can often survive ''in situ'' conditions. Epoxidations of electron-rich double bonds have yielded intermediates of [[Rubottom oxidation]]. Upon hydrolysis, these siloxyepoxides yield α-hydroxyketones.<ref>Adam, W.; Hadjiarapoglou, L.; Wang, X. ''Tetrahedron Lett.'' '''1989''', ''30'', 6497.</ref>
:[[File:DOEpoxScope1.png]]
Electron-poor double bonds take much longer to epoxidize. Heating may be used to encourage oxidation, although the reaction temperature should never exceed 50 °C, to avoid decomposition of the dioxirane.<ref>Adam, W.; Hadjiarapoglou, L.; Nestler, B. ''Tetrahedron Lett.'' '''1990''', ''31'', 331.</ref>
:[[File:DOEpoxScope2.png]]
Alkenes bound to both electron-withdrawing and -donating groups tend to behave like the former, requiring long oxidation times and occasionally some heating. Like electron-poor epoxides, epoxide products from this class of substrates are often stable with respect to hydrolysis.<ref>Yang, D.; Wong, M.-K.; Yip, Y.-C. ''J. Org. Chem.'' '''1995''', ''60'', 3887.</ref>
:[[File:DOEpoxScope3.png]]
In substrates containing multiple double bonds, the most electron-rich double bond can usually be selectively epoxidized.<ref>Messeguer, A.; Fusco, C.; Curci, R. ''Tetrahedron'' '''1993''', ''49'', 6299.</ref>
:[[File:DOEpoxScope4.png]]
Epoxidations employing aqueous Oxone and a catalytic amount of ketone are convenient if a specialized dioxirane must be used (as in asymmetric applications) or if isolation of the dioxirane is inconvenient. Hydrolytic decomposition of the epoxidation product may be used to good advantage.<ref>Denmark, S. E.; Forbes, D. C.; Hays, D. S.; DePue, J. S.; Wilde, R. G. ''J. Org. Chem.'' '''1995''', ''60'', 1391.</ref>
:[[File:DOEpoxScope5.png]]

==Synthetic applications==
Diastereoselective DMD epoxidation of a chiral unsaturated ketone was applied to the synthesis of verrucosan-2β-ol.<ref>Piers, E.; Boulet, S. L. ''Tetrahedron Lett.'' '''1997''', ''38'', 8815.</ref>
:[[File:DOEpoxSynth.png]]
Enantioselective dioxirane epoxidation is critical in a synthetic sequence leading to an analogue of glabrescol. The sequence produced the glabrescol analogue in 31% overall yield in only two steps.<ref>Xiong, Z.; Corey, E. J. ''J. Am. Chem. Soc.'' '''2000''', ''122'', 4831.</ref>
:[[File:DOEpoxStereoSeq.png]]

==Comparison with other methods==
Dioxirane epoxidation is highly versatile, and compares favorably to related peracid oxidations in many respects. Peracids generate acidic byproducts, meaning that acid-labile substrates and products must be avoided.<ref>Dryuk, V. G. ''Russ. Chem. Rev.'' '''1985''', ''54'', 986.</ref> Dioxirane epoxidations using isolated oxidant can be carried out under neutral conditions without the need for aqueous buffering. However, catalytic dioxirane oxidations do require water and are not suitable for hydrolytically unstable substrates.

Some methods are well-suited to the oxidation of electron-rich or electron-poor double bonds, but few are as effective for both classes of substrate as dioxiranes. Weitz-Scheffer conditions (NaOCl, H<sub>2</sub>O<sub>2</sub>/KOH, tBuO<sub>2</sub>H/KOH) work well for oxidations of electron-poor double bonds,<ref>Patai, S.; Rappoport, Z. In ''The Chemistry of Alkenes''; Patai, S., Ed.; Wiley: New York, 1964, Vol. 1, pp. 512–517.</ref> and sulfonyl-substituted [[oxaziridine]]s are effective for electron-rich double bonds.<ref>Davis, F. A.; Sheppard, A. C.; Chen, B.-C.; Haque, M. S. ''J. Am. Chem. Soc.'' '''1990''', ''112'', 6679.</ref>

Metal-based oxidants are often more efficient than dioxirane oxidations in the catalytic mode; however, environmentally unfriendly byproducts are typically generated. In the realm of asymmetric methods, both the [[Sharpless epoxidation]]<ref>Katsuki, T.; Martin, V. S. ''Org. React.'' '''1996''', ''48'', 1.</ref> and [[Jacobsen epoxidation]]<ref>Jacobsen, E. N. In ''Comprehensive Organometallic Chemistry II''; Abel, E. W.; Stone, F. G. A.; Wilkinson, G.; Hegedus, L. S., Eds.; Pergamon: New York, 1995, Vol. 12, Chapter 11.1, pp. 1097–1135.</ref> surpass asymmetric dioxirane oxidations in enantioselectivity. Additionally, enzymatic epoxidations are more enantioselective than dioxirane-based methods; however, operational difficulties and low yields are sometimes associated with enzymatic oxidations<ref>Adam, W.; Lazarus, M.; Saha-Möller, C. R.; Weichold, O.; Hoch, U.; Häring, D.; Schreier P. In ''Advances in Biochemical Engineering/Biotechnology''; Faber, K., Ed.; Springer Verlag: Heidelberg, 1999, Vol. 63, pp. 73–108.</ref>

==Experimental conditions==
Dioxiranes are generated by combining the ketone precursor with a buffered aqueous solution of KHSO<sub>5</sub>. The volatile dioxiranes DMD and TFD are isolated via distillation of the crude reaction mixture. [[Baeyer-Villiger oxidation]] may compete with dioxirane formation. Once isolated, dioxiranes are kept in solutions of the corresponding ketones and dried with [[molecular sieve]]s. [[Air-free technique]] is unnecessary unless the substrate or product is air-sensitive or hydrolytically labile, and most oxidations are carried out in the open air in Erlenmeyer flasks.

Oxidations with ''in situ'' generated dioxiranes are more convenient than isolation methods, provided the substrate is stable towards hydrolysis. Reactions can either be carried out in truly biphasic media with mechanical stirring, or in a homogeneous medium derived from water and a miscible organic solvent, such as [[acetonitrile]]. Asymmetric epoxidations are commonly carried out under the latter conditions. Some ketone catalysts are more persistent under slightly basic homogeneous conditions.


==Mechanism and stereochemistry==
==Mechanism and stereochemistry==

Revision as of 14:21, 4 November 2024

Oxidation with dioxiranes refers to the introduction of oxygen into organic molecules through the action of a dioxirane. Dioxiranes are well known for their oxidation of alkenes to epoxides; however, they are also able to oxidize other unsaturated functionality, heteroatoms, and alkane C-H bonds.[1]

Epoxidation with dioxiranes refers to the synthesis of epoxides from alkenes using dioxiranes.[2]

Dioxiranes are three-membered cyclic peroxides containing a weak oxygen-oxygen bond. Although they are able to effect oxidations of heteroatom functionality and even carbon-hydrogen bonds,[3] they are most widely used as epoxidizing agents of alkenes. Dioxiranes are electrophilic oxidants that react more quickly with electron-rich than electron-poor double bonds; however, both classes of substrates can be epoxidized within a reasonable time frame. Dioxiranes may be prepared and isolated or generated in situ from ketones and potassium peroxymonosulfate (Oxone). In situ preparations may be catalytic in ketone, and if the ketone is chiral, enantioselective epoxidation takes place. The functional group compatibility of dioxiranes is limited somewhat, as side oxidations of amines and sulfides are rapid. Nonetheless, protocols for dioxirane oxidations are entirely metal free. The most common dioxiranes employed for synthesis are dimethyl dioxirane (DMD) and methyl(trifluoromethyl)dioxirane (TFD).

Mechanism and stereochemistry

The mechanism of epoxidation with dioxiranes most likely involves concerted oxygen transfer through a spiro transition state.[4] As oxygen transfer occurs, the plane of the oxirane is perpendicular to and bisects the plane of the alkene pi system. The configuration of the alkene is maintained in the product, ruling out long-lived radical intermediates. In addition, the spiro transition state has been used to explain the sense of selectivity in enantioselective epoxidations with chiral ketones.[5]


Diastereoselective epoxidation may be achieved through the use of alkene starting materials with diastereotopic faces. When racemic 3-isopropylcyclohexene was subjected to DMD oxidation, the trans epoxide, which resulted from attack on the less hindered face of the double bond, was the major product.[6]

Scope and limitations

Dioxiranes may either be prepared in advance or generated in situ for epoxidation reactions. In most cases, a two-phase system must be set up for in situ epoxidations, as KHSO5 is not soluble in organic solvents. Thus, substrates or products sensitive to hydrolysis will not survive in situ epoxidations.[7] This section describes epoxidation conditions for alkenes with electron-donating or -withdrawing substituents, both of which may be epoxidized with dioxiranes in either the stoichiometric or catalytic mode.

Although dioxiranes are highly electrophilic, they epoxidize both electron-rich and electron-poor alkenes in good yield (although the latter react much more slowly). Electron-poor epoxide products also exhibit enhanced hydrolytic stability, meaning that they can often survive in situ conditions. Epoxidations of electron-rich double bonds have yielded intermediates of Rubottom oxidation. Upon hydrolysis, these siloxyepoxides yield α-hydroxyketones.[8]

Electron-poor double bonds take much longer to epoxidize. Heating may be used to encourage oxidation, although the reaction temperature should never exceed 50 °C, to avoid decomposition of the dioxirane.[9]

Alkenes bound to both electron-withdrawing and -donating groups tend to behave like the former, requiring long oxidation times and occasionally some heating. Like electron-poor epoxides, epoxide products from this class of substrates are often stable with respect to hydrolysis.[10]

In substrates containing multiple double bonds, the most electron-rich double bond can usually be selectively epoxidized.[11]

Epoxidations employing aqueous Oxone and a catalytic amount of ketone are convenient if a specialized dioxirane must be used (as in asymmetric applications) or if isolation of the dioxirane is inconvenient. Hydrolytic decomposition of the epoxidation product may be used to good advantage.[12]

Synthetic applications

Diastereoselective DMD epoxidation of a chiral unsaturated ketone was applied to the synthesis of verrucosan-2β-ol.[13]

Enantioselective dioxirane epoxidation is critical in a synthetic sequence leading to an analogue of glabrescol. The sequence produced the glabrescol analogue in 31% overall yield in only two steps.[14]

Comparison with other methods

Dioxirane epoxidation is highly versatile, and compares favorably to related peracid oxidations in many respects. Peracids generate acidic byproducts, meaning that acid-labile substrates and products must be avoided.[15] Dioxirane epoxidations using isolated oxidant can be carried out under neutral conditions without the need for aqueous buffering. However, catalytic dioxirane oxidations do require water and are not suitable for hydrolytically unstable substrates.

Some methods are well-suited to the oxidation of electron-rich or electron-poor double bonds, but few are as effective for both classes of substrate as dioxiranes. Weitz-Scheffer conditions (NaOCl, H2O2/KOH, tBuO2H/KOH) work well for oxidations of electron-poor double bonds,[16] and sulfonyl-substituted oxaziridines are effective for electron-rich double bonds.[17]

Metal-based oxidants are often more efficient than dioxirane oxidations in the catalytic mode; however, environmentally unfriendly byproducts are typically generated. In the realm of asymmetric methods, both the Sharpless epoxidation[18] and Jacobsen epoxidation[19] surpass asymmetric dioxirane oxidations in enantioselectivity. Additionally, enzymatic epoxidations are more enantioselective than dioxirane-based methods; however, operational difficulties and low yields are sometimes associated with enzymatic oxidations[20]

Experimental conditions

Dioxiranes are generated by combining the ketone precursor with a buffered aqueous solution of KHSO5. The volatile dioxiranes DMD and TFD are isolated via distillation of the crude reaction mixture. Baeyer-Villiger oxidation may compete with dioxirane formation. Once isolated, dioxiranes are kept in solutions of the corresponding ketones and dried with molecular sieves. Air-free technique is unnecessary unless the substrate or product is air-sensitive or hydrolytically labile, and most oxidations are carried out in the open air in Erlenmeyer flasks.

Oxidations with in situ generated dioxiranes are more convenient than isolation methods, provided the substrate is stable towards hydrolysis. Reactions can either be carried out in truly biphasic media with mechanical stirring, or in a homogeneous medium derived from water and a miscible organic solvent, such as acetonitrile. Asymmetric epoxidations are commonly carried out under the latter conditions. Some ketone catalysts are more persistent under slightly basic homogeneous conditions.

Mechanism and stereochemistry

Prevailing mechanisms

Epoxidations of alkynes and allenes proceed by concerted mechanisms analogous to epoxidations of simple alkenes.[21] Often, these epoxidized products are unstable and undergo further oxidation reactions via different mechanisms, such as Y-H insertion.

Kinetic studies of heteroatom oxidations have demonstrated that their mechanisms likely proceed by an SN2 process, rather than a single-electron-transfer pathway. An example of heteroatom oxidation is the nucleophilic decomposition of DMD by N-oxides, a side reaction that regenerates the reduced starting material and converts the oxidizing agent to dioxygen and acetone.[22]

(2)

Concerning the mechanism of C-H and Si-H oxidations, two mechanisms have been proposed. The debate centers on whether the oxidation takes place via concerted oxenoid-type insertion or via radical intermediates. A large body of evidence (including analogous oxidations of alkenes and peracid epoxidation) supports the concerted mechanism;[23] however, recent observations of radical reactivity have been made. Complete retention of configuration in oxidations of chiral alkanes rules out the involvement of free, uncaged radicals. However, products of radical decomposition pathways have been observed in some DMD oxidations, suggesting radical intermediates.[24]

(3)

Stereoselective variants

Enantioselective dioxirane oxidations may rely on chiral, non-racemic dioxiranes, such as Shi's fructose-based dioxirane. Enantioselective oxidation of meso-diols with Shi's catalyst, for instance, produces chiral α-hydroxy ketones with moderate enantioselectivity.[25]

(4)

Scope and limitations

Dioxiranes oxidize a wide variety of functional groups. This section describes the substrate scope of dioxirane epoxidation and the products that most commonly result.

Oxidations of alkynes, allenes, arenes, and other unique unsaturated functionality may yield epoxides or other oxidized products. Oxidation of allenes affords allene dioxides or products of intramolecular participation.[26] Minor amounts of side products derived from additional oxidation or rearrangement were also observed.

(6)

In oxidations of heteroaromatic compounds, the products obtained depend on reaction conditions. Thus, at low temperatures, acetylated indoles are simply epoxidized in high yield (unprotected indoles undergo N-oxidation). However, when the temperature is raised to 0 °C, rearranged products are obtained.[27]

(7)

DMD may oxidize heteroatoms to the corresponding oxides (or products of oxide decomposition). Often, the results of these oxidations depend on reaction conditions. Tertiary amines cleanly give the corresponding N-oxides.[28] Primary amines give nitroalkanes upon treatment with 4 equivalents of DMD, but azoxy compounds upon treatment with only 2 equivalents.[29] Secondary amines afford either hydroxylamines or nitrones.[30]

(8)

Oxidation of nitronate anions, generated in situ from nitroalkanes, leads to carbonyl compounds in an example of an oxidative Nef reaction.[31]

(9)

Sulfide oxidation in the presence of a single equivalent of DMD leads to sulfoxides.[32] Increasing the amount of DMD used (2 or more equivalents) leads to sulfones. Both nitrogen and sulfur are more susceptible to oxidation than carbon-carbon multiple bonds.

(10)

Although alkanes are typically difficult to functionalize directly, C-H insertion with TFD is an efficient process in many cases. The order of reactivity of C-H bonds is: allylic > benzylic > tertiary > secondary > primary. Often, the intermediate alcohols produced are oxidized further to carbonyl compounds, although this can be prevented by trapping in situ with an anhydride. Chiral alkanes are functionalized with retention of configuration.[33]

(11)

Dioxiranes oxidize primary alcohols to either the aldehyde or carboxylic acid;[34] however, DMD selectively oxidizes secondary over primary alcohols. Thus, vicinal diols may be transformed into α-hydroxy ketones with dioxirane oxidation.[35]

(12)

Epoxidation is usually more facile than C-H oxidation, although sterically hindered allyl groups may undergo selective C-H oxidation instead of epoxidation of the allylic double bond.[36]

Comparison with other methods

A variety of alternative heteroatom oxidation reagents are known, including peroxides (often employed with a transition metal catalyst) and oxaziridines. These reagents do not suffer from the over-oxidation problems and decomposition issues associated with dioxiranes; however, their substrate scope tends to be more limited. Nucleophilic decomposition of dioxiranes to singlet oxygen is a unique problem associated with dioxirane heteroatom oxidations. Although chiral dioxiranes do not provide the same levels of enantioselectivity as other protocols, such as Kagan's sulfoxidation system,[37] complexation to a chiral transition metal complex followed by oxidation affords optically active sulfoxides with good enantioselectivity.

Oxidation of arenes and cumulenes leads initially to epoxides. These substrates are resistant to many epoxidation reagents, including oxaziridines, hydrogen peroxide, and manganese oxo compounds. Organometallic oxidants also react sluggishly with these compounds, with the exception of methyltrioxorhenium.[38] Peracids also react with arenes and cumulenes, but cannot be employed with substrates containing acid-sensitive functionality.

The direct oxidative functionalization of C-H bonds is an ongoing problem in oxidation chemistry. Among metal-free systems, dioxiranes are the best oxidants for the conversion of C-H bonds to alcohols or carbonyls. However, some catalytic transition-metal systems, such as White's palladium-sulfoxide system, are able to oxidize C-H bonds selectively.[39]

References

  1. ^ Adam, W.; Zhao, C.-G.; Jakka, K. Org. React. 2007, 69, 1. doi:10.1002/0471264180.or069.01
  2. ^ Adam, W.; Saha-Moller, C.; Zhao, C.-G. Org. React. 2003, 61, 219. doi:10.1002/0471264180.or061.02
  3. ^ Adam, W.; Zhao, C.-G.; Jakka, K. Org. React. 2007, 69, 1.
  4. ^ Houk, K. N.; Liu, J.; DeMello, N. C.; Condroski, K. R. J. Am. Chem. Soc. 1997, 119, 10147.
  5. ^ Wang, Z.-X.; Tu, Y.; Frohn, M.; Zhang, J.-R.; Shi, Y. J. Am. Chem. Soc. 1997, 119, 11224.
  6. ^ Adam, W.; Mitchell, C. M.; Saha-Möller, C. R. Eur. J. Org. Chem. 1999, 785.
  7. ^ Denmark, S. E.; Wu, Z. J. Org. Chem. 1998, 63, 2810.
  8. ^ Adam, W.; Hadjiarapoglou, L.; Wang, X. Tetrahedron Lett. 1989, 30, 6497.
  9. ^ Adam, W.; Hadjiarapoglou, L.; Nestler, B. Tetrahedron Lett. 1990, 31, 331.
  10. ^ Yang, D.; Wong, M.-K.; Yip, Y.-C. J. Org. Chem. 1995, 60, 3887.
  11. ^ Messeguer, A.; Fusco, C.; Curci, R. Tetrahedron 1993, 49, 6299.
  12. ^ Denmark, S. E.; Forbes, D. C.; Hays, D. S.; DePue, J. S.; Wilde, R. G. J. Org. Chem. 1995, 60, 1391.
  13. ^ Piers, E.; Boulet, S. L. Tetrahedron Lett. 1997, 38, 8815.
  14. ^ Xiong, Z.; Corey, E. J. J. Am. Chem. Soc. 2000, 122, 4831.
  15. ^ Dryuk, V. G. Russ. Chem. Rev. 1985, 54, 986.
  16. ^ Patai, S.; Rappoport, Z. In The Chemistry of Alkenes; Patai, S., Ed.; Wiley: New York, 1964, Vol. 1, pp. 512–517.
  17. ^ Davis, F. A.; Sheppard, A. C.; Chen, B.-C.; Haque, M. S. J. Am. Chem. Soc. 1990, 112, 6679.
  18. ^ Katsuki, T.; Martin, V. S. Org. React. 1996, 48, 1.
  19. ^ Jacobsen, E. N. In Comprehensive Organometallic Chemistry II; Abel, E. W.; Stone, F. G. A.; Wilkinson, G.; Hegedus, L. S., Eds.; Pergamon: New York, 1995, Vol. 12, Chapter 11.1, pp. 1097–1135.
  20. ^ Adam, W.; Lazarus, M.; Saha-Möller, C. R.; Weichold, O.; Hoch, U.; Häring, D.; Schreier P. In Advances in Biochemical Engineering/Biotechnology; Faber, K., Ed.; Springer Verlag: Heidelberg, 1999, Vol. 63, pp. 73–108.
  21. ^ Adam, W.; Saha-Moller, C.; Jakka, K. Org. React. 2002, 61, 219.
  22. ^ Adam, W.; Briviba, K.; Duschek, F.; Golsch, D.; Kiefer, W.; Sies, H. J. Chem. Soc., Chem. Commun. 1995, 1831.
  23. ^ Mello, R.; Fiorentino, M.; Fusco, C.; Curci, R. J. Am. Chem. Soc. 1989, 111, 6749.
  24. ^ Bravo, A.; Fontana, F.; Fronza, G.; Minisci, F.; Zhao, L. J. Org. Chem. 1998, 63, 254.
  25. ^ Adam, W.; Saha-Möller, C. R.; Zhao, C.-G. J. Org. Chem. 1999, 64, 7492.
  26. ^ Crandall, J. K.; Batal, D. J.; Lin, F.; Reix, T.; Nadol, G. S.; Ng, R. A. Tetrahedron 1992, 48, 1427.
  27. ^ Adam, W.; Ahrweiler, M.; Peters, K.; Schmiedeskamp, B. J. Org. Chem. 1994, 59, 2733.
  28. ^ Ferrer, M.; Sánchez-Baeza, F.; Messeguer, A. Tetrahedron 1997, 53, 15877.
  29. ^ Murray, R. W.; Singh, M.; Rath, N. Tetrahedron: Asymmetry 1996, 7, 1611.
  30. ^ Murray, R. W.; Singh, M.; Jeyaraman, R. J. Am. Chem. Soc. 1992, 114, 1346.
  31. ^ Pinnick, Harold W. (1990). "The Nef Reaction". Organic Reactions. Vol. 38. pp. 655–792. doi:10.1002/0471264180.or038.03. ISBN 978-0-471-26418-7.
  32. ^ Murray, R. W.; Jeyaraman, R. J. Org. Chem. 1985, 50, 2847.
  33. ^ Asensio, G.; Mello, R.; González-Núñez, M. E.; Castellano, G.; Corral, J. Angew. Chem. Int. Ed. Engl. 1996, 35, 217.
  34. ^ Curci, R. J. Am. Chem. Soc. 1991, 113, 2205.
  35. ^ Bovicelli, P.; Lupattelli, P.; Sanetti, A.; Mincione, E. Tetrahedron Lett. 1994, 35, 8477.
  36. ^ Adam, W.; Prechtl, F.; Richter, M. J.; Smerz, A. K. Tetrahedron Lett. 1995, 36, 4991.
  37. ^ Pitchen, P.; Dunach, E.; Deshmukh, M. N.; Kagan, H. B. J. Am. Chem. Soc. 1984, 106, 8188.
  38. ^ Adam, W.; Mitchell, C. M.; Saha-Möller, C. R.; Weichold, O. In Structure and Bonding, Metal-Oxo and Metal-Peroxo Species in Catalytic Oxidations; Meunier, B., Ed.; Springer Verlag: Berlin Heidelberg, 2000; Vol. 97, pp 237–285.
  39. ^ N.A. Vermeulen; M.S. Chen; and M.C. White. Tetrahedron 2009, 65, 3078.
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