- Use of flash vacuum thermolysis in a stereocontrolled synthesis of optically active alkyl-substituted cyclopentenones with fragrant properties
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The synthesis of four pairs of enantiopure antipodal substituted cyclopentenones is described. The synthetic sequences first comprise the preparation of a tricyclo[5.2.1.02,6]deca-4,8-dienone system, a subsequent kinetic enzymatic resolution of the appropriately functionalized tricyclic system, followed by a series of chemical transformations to install the desired substituents, and finally a retro Diels-Alder reaction using flash vacuum thermolysis to give the target products in high chemical and optical yields. The strategy makes effective use of the concept of transient chirality involving complete stereochemical control over reactions with the chiral tricyclic systems before thermal removal of the cyclopentadiene.
- Zwanenburg, Binne,Volkers, Andries A.,Klunder, Antonius J. H.
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p. 1234 - 1242
(2014/10/16)
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- Chemoselective epoxidation of electron rich and electron deficient olefins catalyzed by meso-tetraarylporphyrin iron(iii) chlorides in imidazolium ionic liquids
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The oxygenation of substrates containing both electron rich and electron deficient olefins (1a-b) catalyzed by 5,10,15,20-tetraarylporphyrinatoiron(iii) chlorides [TAPFe(iii)Cl] with H2O2 gave epoxides at both electron rich and deficient olefin (2a-b, 3a-b), while with iodosyl benzene (PhIO) gave the epoxides only at electron rich olefin (3a-b) in imidazolium ionic liquids (ILs). Further reaction of 2a-b with sodium hydroxide in methanol gave 4a-b by base catalysed rearrangement of enedione epoxides. Similar reaction of 4a-b with H2O2 or PhIO gave the major epoxides of electron deficient olefins and electron rich olefins. The ferric peroxy anions (TAP-FeIII-OO-) are effective intermediates in the epoxidation of electron deficient olefins, whereas the high valent oxoferrylporphyrin π-cation radicals (TAP-FeIVO+) are involved in the epoxidation of electron rich olefins. The ILs provide the special microenvironments by the interactions of cations and anions, in which the generation of the active intermediates from TAPFe(iii)Cl/[Bmim][PF 6] and monooxygen donors could be accelerated significantly. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012.
- Singh, Pradeep Pratap,Ambika,Chauhan
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experimental part
p. 650 - 655
(2012/05/04)
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- Polymer-supported Oxone and tert-butyl hydroperoxide: new reagents for the epoxidation of α,β-unsaturated aldehydes and ketones
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Efficient, mild and selective epoxidation of α,β-unsaturated aldehydes and ketones was performed using polyvinylpyrrolidonesupported Oxone (Oxone/PVP) and ButOOH/PVP.
- Pourali, Ali Reza
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experimental part
p. 113 - 115
(2010/06/19)
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- Synthetic access to the chlorocyclopentane cores of the proposed original and revised structures of palau'amine
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(Chemical Equation Presented) Core knowledge: The synthesis of the functionalized cores of both the originally proposed and revised structures of palau'amine have been achieved (see structures). A Diels-Alder/[3,3]-sigmatropic rearrangement sequence and a Beckmann rearrangement enable the stereo-controlled formation of the highly congested cores.
- Bultman, Michael S.,Ma, Jun,Gin, David Y.
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supporting information; experimental part
p. 6821 - 6824
(2009/04/07)
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- Enantioselective total synthesis of epoxyquinone natural products (-)-phyllostine, (+)-epoxydon, (+)-epiepoxydon and (-)-panepophenanthrin: Access to versatile chiral building blocks through enzymatic kinetic resolution
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A new enzyme mediated protocol to access versatile chiral building blocks for the synthesis of epoxyquinone natural products is delineated. Total syntheses of (-)-phyllostine, (+)-epoxydon, (+)-epiepoxydon and (-)-panepophenanthrin have been accomplished to demonstrate the efficacy of this approach.
- Mehta, Goverdhan,Islam, Kabirul
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p. 7683 - 7687
(2007/10/03)
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- Enantioselective total synthesis of (-)-epoxyquinols a and B. Novel, convenient access to chiral epoxyquinone building blocks through enzymatic desymmetrization
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Following our recent total synthesis of the biologically potent natural products epoxyquinols A and B in racemic form, we have now accomplished the total synthesis of the (-)-epoxyquinols A and B, anti-podes of the angiogenesis inhibiting natural products, through a protocol that involves enzymatic desymmetrization of a versatile epoxyquinone derivative, readily available from the Diels-Alder adduct of cyclopentadiene and p-benzoquinone.
- Mehta, Goverdhan,Islam, Kabirul
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p. 3611 - 3615
(2007/10/03)
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- Total synthesis of the novel angiogenesis inhibitors epoxyquinols A and B
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The synthesis of the recently discovered angiogenesis inhibitors epoxyquinols A and B, having novel polyketide derived dimeric structures, has been accomplished from the readily available Diels-Alder adduct of cyclopentadiene and p-benzoquinone through a short, simple and flexible strategy that is diversity oriented and can be adapted to an asymmetric variant.
- Mehta, Goverdhan,Islam, Kabirul
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p. 3569 - 3572
(2007/10/03)
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- Intermediates and improved processes for the preparation of neplanocin A
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Intermediate compounds, including 2-(t-butyldimethylsilyloxymethyl)-3,4-[(dimethylmethylene)dioxy]-5-hydroxy-tricyclo[5.2.1.02,6]dec-8-ene, which are useful for the synthesis of neplanocin A having strong antitumor activity. Improved processes for the preparation of neplanocin A, starting from optically active 2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.02,6]deca-3,8-diene and via a key step comprising a retro-Diels-Alder reaction of the above intermediate.
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- A new catalytic and enantioselective desymmetrization of symmetrical methylidene cycloalkene oxides
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(equation presented) Chiral copper complexes of C2-symmetrical phosphoroamidites were found to be highly effective catalysts for both kinetic resolution and novel desymmetrization reactions of new methylidene epoxycycloalkanes.
- Bertozzi, Fabio,Crotti, Paolo,Macchia, Franco,Pineschi, Mauro,Arnold, Alexander,Feringa, Ben L.
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p. 933 - 936
(2007/10/03)
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- Stereoselctive Total Syntheses of Conduritols-F and -A from Tricyclo2,7>undeca-4,9-dien-3,6-dione
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Effective syntheses of conduritols-F and A have been accomplished starting from cyclopentadiene/benzoquinone adduct 6.Key intermediates are tricyclic acetates 9 and 15 which, when subjected to flash vacuum thermolysis, afford epoxycyclohexene diacetate 10 and cyclohexadiene diacetate 17, respectively.Conduritol-F is obtained from 10 by hydrolysis while conduritol-A is produced from 17 by osmylation.In both cases the final step involves removal of the acetate groups by amidation with ammonia.
- Mgani, Quintino A.,Klunder, Antonius J. H.,Nkunya, Mayunga H. H.,Zwanenburg, Binne
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p. 4661 - 4664
(2007/10/02)
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- NUCLEOPHILIC ELIMINATIVE RING FISSION OF BRIDGEHEAD SUBSTITUTED 1,3-BISHOMOCUBYL ACETATES
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The base induced cage fission of three different types of functionalized bridgehead substituted 1,3-bishomocubyl acetates, viz A, B and C is described.The synthesis of two 6-functionalized 1,3-bishomocubyl 4-acetates (type A), viz 4-acetoxypentacyclo2,5.03,9.04,8>decan-6-one 5 and its ethylene acetal 6 has been accomplished starting from the readily available Diels-Alder adduct 4.The synthesis of three 1,3-bishomocubyl 8-acetates (type B), viz 8-acetoxypentacyclo2,5.03,9.04,8>decan-6-one 15, its ethylene acetal 16 and the parent acetate 20has been carried out starting from the cyclopentadiene-benzoquinone adduct 7.Base induced homoketonization of 6, 16 and 20 leads regio- and stereospecifically to the thermodynamically favored half cage ketones 22, 28 and 31, respectively.In constrast, the cage opening of the β-ketoacetates 5 and 15 is essentially directed by the β-ketone function.In the case of 5, regiospecific cleavage of the central C4-C5 bond is observed producing in a stereospecific manner diketone 25 in quantitative yield.Under similar conditions, acetate 15 gives a complex mixture of cage opened products arising from further fragmentation of the initially formed diketone 34.Deuterium labeling experiments reveal an anti-Bredt behavior of half cage ketones 28 and 31.The synthesis of a bridgehead acetate of type C has been accomplished by stereoselective reduction of ketone acetate 5 with LiAlH(t-OBu)3 followed by mesylation.A mixture of epimers 36a and 36b (ratio 1:4) is obtained from which the predominant anti-epimer 36b could be isolated.An X-ray analysis established its structure.Base induced cage fission of 36b leads regiospecifically totetracyclo2,5.04,8>decenone 37.In constrast the syn-epimer 36a, under similar conditions, only affords the bridgehead alcohol 38.
- Klunder, A. J. H.,Valk, W. C. G. M. de,Verlaak, J. M. J.,Schellekens, J. W. M.,Noordik, J. H.,et al.
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p. 963 - 973
(2007/10/02)
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