- Carbohydrate-derived iminium salt organocatalysts for the asymmetric epoxidation of alkenes
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A new family of carbohydrate-based dihydroisoquinolinium salts has been prepared and tested for potential as asymmetric catalysts for the epoxidation of unfunctionalized alkene substrates, providing up to 57% ee in the product epoxides.
- Bulman Page, Philip C.,Chan, Yohan,Liddle, John,Elsegood, Mark R.J.
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p. 7283 - 7305
(2017/09/13)
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- N-Substituted 3,4-dihydroisoquinolinium ionic liquids as catalysts in alkenes epoxidation reactions
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Because of their high reactivity, epoxides are one of the most important groups of organic compounds. These substances are synthesised primarily by the catalytic oxidation of alkenes in the liquid or gaseous phase. This study investigated new catalytic systems for epoxidation reactions using functionalised ionic liquids. These ionic liquids serve as oxygen transfer agents during the reactions. Several N-substituted 3,4-dihydroisoquinolinium ionic liquids were synthesised, and their potential as catalysts for epoxidation reactions was investigated. Cyclic alkenes such as cyclohexene and cyclooctene were used as model olefins.
- Baj, Stefan,Be?ch, MacIej,Gibas, Miros?aw
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scheme or table
p. 197 - 205
(2012/09/08)
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- Cascade condensation, cyclization, intermolecular dipolar cycloaddition by multi-component coupling and application to a synthesis of (±)-crispine A
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A general approach for the synthesis of various nitrogen-containing heterocyclic compounds is described using an intermolecular dipolar cycloaddition reaction of azomethine ylides and nitrones. Stabilized and non-stabilized azomethine ylide dipoles or the related nitrones were generated by condensation of 4-, 5- or 6-halo-aldehydes with a readily available amino-acid, amino-ester or hydroxylamine to give an imine followed by cyclization and either decarboxylation or loss of a proton. After intermolecular cycloaddition with an activated dipolarophile, bicyclic or polycyclic (if the ylide dipole and/or dipolarophile contain a ring) amines were produced. A short synthesis of the alkaloid (±)-crispine A was achieved based on this tandem/domino 3-component coupling chemistry.
- Coldham, Iain,Jana, Samaresh,Watson, Luke,Martin, Nathaniel G.
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scheme or table
p. 1674 - 1679
(2009/06/27)
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- Highly efficient catalysts for epoxidation mediated by iminium salts
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A range of substituted dihydroisoquinolinium salts has been tested in the catalytic epoxidation of several alkenes. Catalyst loadings as low as 0.5 mol% have been used in the epoxidation of 1-phenylcyclohexene. Georg Thieme Verlag Stuttgart.
- Bulman Page, Philip C.,Buckley, Benjamin R.,Appleby, Louise F.,Alsters, Paul A.
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p. 3405 - 3411
(2007/10/03)
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- Functionalized iminium salt systems for catalytic asymmetric epoxidation
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A range of dihydroisoquinolinium salts containing alcohol, ether, and acetal functionalities in the nitrogen substituent has been prepared and tested as asymmetric epoxidation catalysts, providing ee's of up to ca. 60%.
- Page,Rassias,Barros,Ardakani,Buckley,Bethell,Smith,Slawin
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p. 6926 - 6931
(2007/10/03)
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- Dihydroisoquinolinium salts: Catalysts for asymmetric epoxidation
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A range of dihydroisoquinolinium salts were prepared and tested as asymmetric epoxidation catalysts. The factors affecting enantioselectivity of catalytic asymmetric epoxidation process were also discussed. The asymmetric epoxidation reaction employed alkaline hydrogen peroxide and a chiral polypeptide derived from a naturally occurring amino acid, leucine.
- Page, Philip C. Bulman,Rassias, Gerasimos A.,Barros, David,Bethell, Donald,Schilling, Mark B.
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p. 3325 - 3334
(2007/10/03)
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- Development of large-scale syntheses of ropinirole in the pursuit of a manufacturing process
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Two plant syntheses of ropinirole {4-[2-(di-n-propyIamino)-ethyl]-1,3-dihydro-2H-indolin-2-one hydrochloride, SK&F-101468-A} using the ferric chloride mediated cyclisation of β-nitrostyrenes to form 3-chlorooxindoles as the key step are described. The first synthesis suffered the severe limitation of the final-step chemistry being nonselective in the reaction between di-n-propylamine and the bromide precursor to ropinirole as both substitution and elimination pathways were promoted and by-product formation at a level of 40% resulted. This problem was rectified in the latter synthesis by the more selective reaction between di-n-propylamine and the sulfonate ester precursor promoting ropinirole formation to a level of 88%. This second synthesis is now used as the commercial route, and problems (and their solutions) identified during the development of this route are now described. The identification of novel by-products which enabled the Sommelet oxidation step to be optimised is also reported. A unimolecular decomposition mechanism during hydrolysis of the hexaminium salt to form the key benzaldehyde intermediate is proposed and substantiated with experimental data.
- Hayler, John D.,Howie, Simon L. B.,Giles, Robert G.,Negus, Alan,Oxley, Paul W.,Walsgrove, Timothy C.,Whiter
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- Some synthetic approaches to ropinirole (SK and F 101468-A): A potent dopamine receptor agonist
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Three new routes to ropinirole (SK and F 101468-A, 1) are described each involving the preparation of 3-chlorooxindole intermediates of type 3 from β-nitrostyrenes as the pivotal step. The superiority of sulphonate esters 17a-c as direct precursors to 1 over the bromide 11 is also described.
- Hayler,Howie,Giles,Negus,Oxley,Walsgrove,Walsh,Dagger,Fortunak,Mastrocola
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p. 875 - 882
(2007/10/02)
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- Intramolecular Generation of Oxonium Ylides from Functionalized Arylcarbenes
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Arylcarbenes carrying alkoxyalkyl groups in the ortho position have been generated by flash pyrolysis and photolysis of appropriate tosylhydrazone sodium salts.In the gas phase and in a aprotic solvents, interaction of the carbenes with the lone electron pairs of oxygen competes efficiently with insertion into C-H bonds.Both five- and six-membered cyclic oxonium ylides have been generated.The ylides 23, 37, 61b, and 74 undergo 1,2 shifts of benzyl groups with ease, even if ring contraction to highly strained benzocyclobutenes is involved (23, 74).The oxonium ylides37 and 61b strongly prefer the nonconcerted Stevens rearrangement to the sigmatropic Sommelet rearrangement, in contrast to analogous ammonium ylides.Alkyl shifts occur to a very minor extent, if at all.Evidence is presented that alcohols intercept both the carbenes and the oxonium ylides.Protonation of the ylides leads to cyclic oxonium ions, which undergo nucleophilic cleavage of the C-O bonds.Acid catalyzed decomposition of the appropriate diazo compounds gives rise to six-membered, but not to five-membered, cyclic oxonium ions, thus confirming the different intramolecular reactivities of arylcarbenes and benzyl cations.The efficiency of carbene interception increases with increasing acidity of the medium, suggesting nucleophilic behavior (protonation) of the arylcarbenes.
- Kirmse, Wolfgang,Kund, Klaus
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p. 1465 - 1473
(2007/10/02)
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