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.C.Tetrahedron Asymmetry 1998, 9, 3745-3749.(3) Yao, H.; Richardson, D.E.J.Am.Chem.Soc.2000, 122, 3220-3221.of explosion.The reaction is run at room temperature in solvents10.1021/ja004000a CCC: $20.00 © 2001 American Chemical SocietyPublished on Web 03/02/2001 2934 J.Am.Chem.Soc., Vol.123, No.12, 2001 Communications to the Editorthat are amenable to process chemistry, and no halogenated liquids Table 1.Epoxidations of Representative Alkenesor ones with low flash points are required.No organic ligands oradditives are used, and this facilitates isolation of the desiredepoxide.It is difficult to be certain that the process reported here iscompletely unprecedented because studies involving transition-metal salts and hydrogen peroxide are so ubiquitous.5 However,it is clear that these Mn-catalyzed reactions are much cleaner thanFenton s6 and related systems that generate hydroxyl radicals.7Several groups have reported epoxidation reactions using H2O2mediated by TACN-manganese complexes,8,9 but the catalyststend to be relatively inaccessible or require larger excesses ofhydrogen peroxide.9-11 One of these studies mentions MnCl2 asa control, and epoxidation activity was detected, but this findingwas not exploited.10 Most importantly, in prior studies of metal-catalyzed epoxidations the special importance of bicarbonate inthe media has either not been investigated, realized, or empha-sized.Investigations to elucidate the role of bicarbonate are inprogress.Our working hypothesis is that percarbonate (HCO4-)formed in situ12 combines with the manganese to give the activeintermediate.Nearly all of the existing methods for using hydrogen peroxideas an epoxidation reagent have clear disadvantages compared withthe one reported here.For instance, most of them involve acidicreagents that tend to decompose the epoxide products.13 One not-able exception is catalytic methyltrioxorhenium (MTO)14 bufferedwith pyridine.15 However, that procedure features a much moreexpensive catalyst and media that are explosive or environmentallyhazardous, that is, nitromethane or dichloromethane.Moreover,separation of acid-sensitive epoxides from pyridine is likely tobe inconvenient for many substrates.On the other hand, theprotocol reported here requires 10 equiv of H2O2 to drive thereaction to completion, whereas near stoichiometric amounts areused in the MTO/pyridine method.The two procedures are(4) Large-Scale Synthesis of Cyclooctene Oxide: DMF (1.68 L) and MnSO4(1.69 g, 0.01 mol) were placed in a 12 L three-neck flask, equipped with amechanical stirrer and a vent to an oil bubbler.Cyclooctene (110 g, 1.00 mol)was added all at once.The flask was then placed in a water bath at 20 °C(cryocooler).A 3 L two-neck flask equipped with a magnetic stirrer, wascharged with 20.6 g of NaHCO3, 0.123 g of Na2CO3, and 1.2 Lof H2O, andthe pH of the resulting solution was adjusted to 8.0 with 1 M HCl.The flaskwas then placed into a water bath maintained at 1 °C and then 1.1 L of 30%H2O2 was added all at once.The aqueous solution of buffer/peroxide wasthen added dropwise to the DMF solution over a period of 36 h via a cannula.CAUTION! The reaction exotherms if the buffer/peroxide solution is addedtoo quickly or if heat transfer from the receiving flask is inadequate to maintainthe desired temperature.The reaction mixture was extracted into Et2O (900mL × 4), washed with brine (900 mL), and dried (Na2SO4).The organicfraction was concentrated, and residual DMF was fractionally distilled fromit at 5 mmHg.The final product was purified via bulb-to-bulb distillation at5 mmHg and 57 °C oven temperature, 84.5 g, mp ) 53-55 °C.Small-ScaleEpoxidation Procedure: Similar to the above except that 23 mL of DMF and17 mL of 0.2 M NaHCO3(aq) were used per 1 mmol of substrate.The aqueousmixture of H2O2 and NaHCO3 was added dropwise over a period of 16 h.aUnless otherwise specified, the reactions were performed using 0.01(5) Jones, C.W.Applications of Hydrogen Peroxide and DeriVatiVes; MPGequiv of MnSO4 on a 1 mmol scale; yields determined by NMR or GCBooks Ltd.: Cornwall, UK, 1999.b cversus an internal standard.1 mol scale.The corresponding(6) Boguslavskaya, L.S.Russ.Chem.ReV.1965, 34, 503-15.danthraquinone (35%) was also observed.trans-3-Phenylpropenal was(7) Sheldon, R.A.; Kochi, J.K.Metal-Catalyzed Oxidations of Organicet fCompounds; Academic Press: New York, 1981.also observed (16%).BuOH used in place of DMF.Isolated as theg h(8) Vos, D.E.D.; Meinershagen, J.L.; Bein, T.Angew.Chem., Int.Ed.methyl ester.001 equiv of MnSO4 were used.1 mol scale.Engl.1996, 35, 2211-3; Vos, D.E.D.; Sels, B.F.; Reynaers, M.; Rao, Y.V.S.; Jacobs, P.A.Tetrahedron Lett.1998, 39, 3221-4.(9) Bolm, C.; Kadereit, D.; Valacchi, M.Synlett 1997, 687-8.complementary insofar as aliphatic terminal alkenes are epoxi-(10) Hage, R.; Iburg, J.E.; Kerschner, J.; Koek, J.H.; Lempers, E.L.M.;dized by MTO/pyridine, whereas selective epoxidation of theMartens, R.J.; Racheria, U.S.; Russell, S.W.; Swarthoff, T.; Vliet, M.R.P.v.; Warnaar, J.B.; Wolf, L.v.d.; Krijnen, B.Nature 1994, 369, 637-9.nonterminal alkenes in the presence of monosubstituted, aliphatic(11) Quee-Smith, V.C.; DelPizzo, L.; Jureller, S.H.; Kerschner, J.L.;alkenes is possible in the Mn-catalyzed reactions.In summary,Hage, R.Inorg.Chem.1996, 35, 6461-5; Vos, D.D.; Bein, T.Chem.the epoxidation protocol presented here has the potential to fulfillCommun.1996, 917-8; Vos, D.E.D.; Wildeman, S.d.; Sels, B.F.; Grobet,P.J.; Jacobs, P.A.Angew.Chem., Int.Ed.1999, 38, 980-3; Brinksma, J.; unmet needs in exploratory syntheses and large-scale reactions.Hage, R.; Kerschner, J.; Feringa, B.L.Chem.Commun.2000, 537-8.Acknowledgment.We thank Dr.D.E.Richardson, University of(12) Richardson, D.E.; Yao, H.; Frank, K.M.; Bennett, D.A.J.Am.Chem.Florida, for helpful discussions.This research was supported by TheSoc.2000, 122, 1729-39.Robert A.Welch Foundation.(13) Jorgensen, K.A.Chem.ReV.1989, 89, 431-58; Sato, K.; Aoki, M.;Supporting Information Available: Outlines of optimization pro-Ogawa, M.; Hashimoto, T.; Noyori, R.J.Org.Chem.1996, 61, 8310-1.(14) Herrmann, W.A.; Fischer, R.W.; Marz, D.W.Angew.Chem., Int.cedures, pilot kinetic study to show dependence of reaction rate onEd.Engl.1991, 30, 1638-41.manganese concentration (PDF).This material is available free of charge(15) Rudolph, J.; Reddy, K.L.; Chiang, J.P.; Sharpless, K.B.J.Am.Chem.via the Internet at http://pubs.acs.org.Soc.1997, 119, 6189-90; Adolfsson, H.; Converso, A.; Sharpless, K.B.Tetrahedron Lett.1999, 40, 3991-4.JA004000A [ Pobierz caÅ‚ość w formacie PDF ]
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.C.Tetrahedron Asymmetry 1998, 9, 3745-3749.(3) Yao, H.; Richardson, D.E.J.Am.Chem.Soc.2000, 122, 3220-3221.of explosion.The reaction is run at room temperature in solvents10.1021/ja004000a CCC: $20.00 © 2001 American Chemical SocietyPublished on Web 03/02/2001 2934 J.Am.Chem.Soc., Vol.123, No.12, 2001 Communications to the Editorthat are amenable to process chemistry, and no halogenated liquids Table 1.Epoxidations of Representative Alkenesor ones with low flash points are required.No organic ligands oradditives are used, and this facilitates isolation of the desiredepoxide.It is difficult to be certain that the process reported here iscompletely unprecedented because studies involving transition-metal salts and hydrogen peroxide are so ubiquitous.5 However,it is clear that these Mn-catalyzed reactions are much cleaner thanFenton s6 and related systems that generate hydroxyl radicals.7Several groups have reported epoxidation reactions using H2O2mediated by TACN-manganese complexes,8,9 but the catalyststend to be relatively inaccessible or require larger excesses ofhydrogen peroxide.9-11 One of these studies mentions MnCl2 asa control, and epoxidation activity was detected, but this findingwas not exploited.10 Most importantly, in prior studies of metal-catalyzed epoxidations the special importance of bicarbonate inthe media has either not been investigated, realized, or empha-sized.Investigations to elucidate the role of bicarbonate are inprogress.Our working hypothesis is that percarbonate (HCO4-)formed in situ12 combines with the manganese to give the activeintermediate.Nearly all of the existing methods for using hydrogen peroxideas an epoxidation reagent have clear disadvantages compared withthe one reported here.For instance, most of them involve acidicreagents that tend to decompose the epoxide products.13 One not-able exception is catalytic methyltrioxorhenium (MTO)14 bufferedwith pyridine.15 However, that procedure features a much moreexpensive catalyst and media that are explosive or environmentallyhazardous, that is, nitromethane or dichloromethane.Moreover,separation of acid-sensitive epoxides from pyridine is likely tobe inconvenient for many substrates.On the other hand, theprotocol reported here requires 10 equiv of H2O2 to drive thereaction to completion, whereas near stoichiometric amounts areused in the MTO/pyridine method.The two procedures are(4) Large-Scale Synthesis of Cyclooctene Oxide: DMF (1.68 L) and MnSO4(1.69 g, 0.01 mol) were placed in a 12 L three-neck flask, equipped with amechanical stirrer and a vent to an oil bubbler.Cyclooctene (110 g, 1.00 mol)was added all at once.The flask was then placed in a water bath at 20 °C(cryocooler).A 3 L two-neck flask equipped with a magnetic stirrer, wascharged with 20.6 g of NaHCO3, 0.123 g of Na2CO3, and 1.2 Lof H2O, andthe pH of the resulting solution was adjusted to 8.0 with 1 M HCl.The flaskwas then placed into a water bath maintained at 1 °C and then 1.1 L of 30%H2O2 was added all at once.The aqueous solution of buffer/peroxide wasthen added dropwise to the DMF solution over a period of 36 h via a cannula.CAUTION! The reaction exotherms if the buffer/peroxide solution is addedtoo quickly or if heat transfer from the receiving flask is inadequate to maintainthe desired temperature.The reaction mixture was extracted into Et2O (900mL × 4), washed with brine (900 mL), and dried (Na2SO4).The organicfraction was concentrated, and residual DMF was fractionally distilled fromit at 5 mmHg.The final product was purified via bulb-to-bulb distillation at5 mmHg and 57 °C oven temperature, 84.5 g, mp ) 53-55 °C.Small-ScaleEpoxidation Procedure: Similar to the above except that 23 mL of DMF and17 mL of 0.2 M NaHCO3(aq) were used per 1 mmol of substrate.The aqueousmixture of H2O2 and NaHCO3 was added dropwise over a period of 16 h.aUnless otherwise specified, the reactions were performed using 0.01(5) Jones, C.W.Applications of Hydrogen Peroxide and DeriVatiVes; MPGequiv of MnSO4 on a 1 mmol scale; yields determined by NMR or GCBooks Ltd.: Cornwall, UK, 1999.b cversus an internal standard.1 mol scale.The corresponding(6) Boguslavskaya, L.S.Russ.Chem.ReV.1965, 34, 503-15.danthraquinone (35%) was also observed.trans-3-Phenylpropenal was(7) Sheldon, R.A.; Kochi, J.K.Metal-Catalyzed Oxidations of Organicet fCompounds; Academic Press: New York, 1981.also observed (16%).BuOH used in place of DMF.Isolated as theg h(8) Vos, D.E.D.; Meinershagen, J.L.; Bein, T.Angew.Chem., Int.Ed.methyl ester.001 equiv of MnSO4 were used.1 mol scale.Engl.1996, 35, 2211-3; Vos, D.E.D.; Sels, B.F.; Reynaers, M.; Rao, Y.V.S.; Jacobs, P.A.Tetrahedron Lett.1998, 39, 3221-4.(9) Bolm, C.; Kadereit, D.; Valacchi, M.Synlett 1997, 687-8.complementary insofar as aliphatic terminal alkenes are epoxi-(10) Hage, R.; Iburg, J.E.; Kerschner, J.; Koek, J.H.; Lempers, E.L.M.;dized by MTO/pyridine, whereas selective epoxidation of theMartens, R.J.; Racheria, U.S.; Russell, S.W.; Swarthoff, T.; Vliet, M.R.P.v.; Warnaar, J.B.; Wolf, L.v.d.; Krijnen, B.Nature 1994, 369, 637-9.nonterminal alkenes in the presence of monosubstituted, aliphatic(11) Quee-Smith, V.C.; DelPizzo, L.; Jureller, S.H.; Kerschner, J.L.;alkenes is possible in the Mn-catalyzed reactions.In summary,Hage, R.Inorg.Chem.1996, 35, 6461-5; Vos, D.D.; Bein, T.Chem.the epoxidation protocol presented here has the potential to fulfillCommun.1996, 917-8; Vos, D.E.D.; Wildeman, S.d.; Sels, B.F.; Grobet,P.J.; Jacobs, P.A.Angew.Chem., Int.Ed.1999, 38, 980-3; Brinksma, J.; unmet needs in exploratory syntheses and large-scale reactions.Hage, R.; Kerschner, J.; Feringa, B.L.Chem.Commun.2000, 537-8.Acknowledgment.We thank Dr.D.E.Richardson, University of(12) Richardson, D.E.; Yao, H.; Frank, K.M.; Bennett, D.A.J.Am.Chem.Florida, for helpful discussions.This research was supported by TheSoc.2000, 122, 1729-39.Robert A.Welch Foundation.(13) Jorgensen, K.A.Chem.ReV.1989, 89, 431-58; Sato, K.; Aoki, M.;Supporting Information Available: Outlines of optimization pro-Ogawa, M.; Hashimoto, T.; Noyori, R.J.Org.Chem.1996, 61, 8310-1.(14) Herrmann, W.A.; Fischer, R.W.; Marz, D.W.Angew.Chem., Int.cedures, pilot kinetic study to show dependence of reaction rate onEd.Engl.1991, 30, 1638-41.manganese concentration (PDF).This material is available free of charge(15) Rudolph, J.; Reddy, K.L.; Chiang, J.P.; Sharpless, K.B.J.Am.Chem.via the Internet at http://pubs.acs.org.Soc.1997, 119, 6189-90; Adolfsson, H.; Converso, A.; Sharpless, K.B.Tetrahedron Lett.1999, 40, 3991-4.JA004000A [ Pobierz caÅ‚ość w formacie PDF ]