- Synthesis of novel 1,4-bissulfonamide ligands for enantioselective addition of diethylzinc to aldehydes
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Several novel chiral sulfonamide ligands based on (1R,2S,4R,5S)-1,4- diamino-2,5-dimethylcyclohexane skeleton have been synthesized and their application in the enantioselective addition of diethylzinc to aldehydes was investigated in the presence of Ti(O
- Yang, Minghua,Sun, Jiangtao,Zhu, Chengjian
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experimental part
p. 1697 - 1702
(2012/01/13)
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- Synthesis of optically active 2,5-dialkylcyclohexane-1,4-diols and their application in the asymmetric oxidation of sulfides
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A simple and efficient approach to obtain optically pure 1,4-diols was established. The asymmetric oxidation of sulfides to sulfoxides with cumyl hydroperoxide in moderate yields and moderate to high enantioselectivities (up to 84%) catalyzed by chiral Ti/ 1,4-diols complexes has been achieved. A 76% ee value was obtained in the asymmetric synthesis of esomeprazole. Georg Thieme Verlag Stuttgart.
- Sun, Jiangtao,Yang, Minghua,Dai, Zhenya,Zhu, Chengjian,Hu, Hongwen
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scheme or table
p. 2513 - 2518
(2009/04/11)
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- C2-Symmetric nitroxides and their potential as enantioselective oxidants
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The synthesis and evaluation of four C2-symmetric nitroxides are presented. The nitroxides were evaluated for their ability to mediate the oxidation of several alcohols and found to have good catalytic activity. One enantioenriched nitroxide was found to kinetically resolve selected secondary alcohols with very modest selectivities.
- Graetz, Benjamin,Rychnovsky, Scott,Leu, Wen-Hao,Farmer, Patrick,Lin, Rong
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p. 3584 - 3598
(2007/10/03)
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- Ozonolysis of 1,4-cyclohexadienes in the presence of methanol and acid. Mechanism and intermediates in the conversion of 1,4-cyclohexadiene derivatives to β-keto esters
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Conditions for the preparation of β-keto esters directly from 1,4-cyclohexadiene derivatives are described. This procedure is a further step in the application of the synthetic methodology, which consists of the combination of Birch reduction of available benzene derivatives followed by ozonolysis. In this work, the syntheses of derivatives of dimethyl γ-keto-α-aminoadipate and dimethyl β-keto glutamate from the corresponding 1,4-cyclohexadiene derivatives are described. The latter compounds are prepared from phenylalanine and phenylglycine, respectively. The study of the ozonolysis of simple alkyl derivatives of 1,4-cyclohexadiene in the presence of methanol, both in the presence and absence of acid, helped to establish the mechanism of this reaction. The proximity of the two double bonds, which are cleaved, leads to the intermediate formation of 1,2-dioxolane derivatives that could be identified by NMR spectroscopy. It is shown that regardless of the regioselectivity of the cleavage of the primary ozonide, which is formed, all 1,2-dioxolane derivatives can lead to β-keto esters. This is due to the equilibrium between these dioxolanes in the presence of methanol and acid.
- Gbara-Haj-Yahia, Isra,Zvilichovsky, Gury,Seri, Noa
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p. 4135 - 4139
(2007/10/03)
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- Enzymatic desymmetrization of a centrosymmetric diacetate
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An enantiomerically pure cyclohexanol was synthesized starting from para-xylene 1. The key steps are a stereoselective twofold hydroboration and a pig liver esterase (PLE)-catalyzed desymmetrization of the centrosymmetric cyclohexanediacetate 4.
- Boehm, C.,Austin, W. F.,Trauner, D.
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- Reaction of Azoalkanes with Isolable Cation Radical Salts
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Three tertiary azoalkanes related in the sense acyclic, cyclic, and bicyclic are shown to evolve nitrogen upon oxidation with stable cation radical salts.Thus azo-tert-octane (ATO), 3,3,6,6-tetramethyl-1,2-diazacyclohexene (TMDAC), and 1,4-dimethyl-2,3-diazabicyclooct-2-ene (Me2DBO) react rapidly with thianthrenium perchlorate (Th(.1+)ClO4(1-)), tris(p-bromophenyl)aminium hexachloroantimonate (TBPA(.1+)SbCl6(1-)), and TBPA(.1+)SbF6(1-).The ether and olefin products, which are formed in high yield in CH2Cl2/MeOH solvent, are not those expected from the usual free-radical decomposition of azoalkanes but instead implicate carbocations.Althrough the reaction stoichiometry clearly requires 2 equiv of cation radical salt to one of azoalkane, the mechanism is not yet clearly defined.A complication in these studies is found in the ability of certain cation radical salts to oxidize more azoalkane than expected based on the 2:1 stoichiometry.
- Engel, Paul S.,Robertson, Donald M.,Scholz, John N.,Shine, Henry J.
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p. 6178 - 6187
(2007/10/02)
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- Composition of Mixtures of Hydrocarbons after BIRCH-Reduction of Substituted Benzenes and Acid Catalyzed Addition of Alcohols to Alkylsubstituted Cyclohexenes and Carbohexa-1,4-dienes
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10 different benzene hydrocarbons 1, indane, tetraline, anisol and phenol are reduced by sodium in liquid ammonia in the presence of methanol to the BIRCH products 2.The product mixture compositions are determined through capillary GLC.On storage at +6 deg C some rearomatization of the 1,4-cyclohexadienes 2 occurs.Data of the 1H- and 13C-.n.m.r. spectra and also mass spectra of the BIRCH 1,4-dienes 2 are given.For comparison 4-alkoxycyclohexenes 4 and 1-alkoxy-1-methylcyclohexanes 8 are prepared and spectroscopically characterized.Acid-catalyzed addition of alcohols to the 1,4-cyclohexadienes systems is a slow process and gives the 4-alkoxy-4-alkylcyclohex-1-enes (4) only in moderate yields up to 30percent.Most of the products are dimers 5 and also oligomers 6 of the parent hydrocarbons 2.
- Beger, J.,Thomas, B.,Vogel, T.,Kirmse, K.,Lang, R.
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p. 481 - 488
(2007/10/02)
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- REVERSAL OF THE REGIOSELECTIVITY OF THE BIRCH REDUCTION OF XYLENES
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The "Photo-Birch" reduction of o-, m-, and p-xylene, using NaBH4, 1,3-dicyanobenzene, and photolysis, gives 1,4-dienes as products.The regioselectivity of these reactions is greatly different from the normal Birch reduction.
- Epling, Gary A.,Florio, Emily
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p. 1469 - 1472
(2007/10/02)
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- A SAFE AND CONVENIENT NEW PROCEDURE FOR REDUCING AROMATIC COMPOUNDS TO BIRCH-TYPE PRODUCTS
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Aromatic compounds can be reduced by a calcium-amine-t-butyl alcohol system to products which are identical to those obtained by a Birch reduction of the same substrates.
- Benkeser, Robert A.,Laugal, James A.,Rappa, Angela
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p. 2089 - 2092
(2007/10/02)
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- Synthesis of Polycyclic Homocyclopropylcarbinols by Reductive Cyclization of Bromocyclopropyl Epoxides
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A new synthetic route to polycyclic homocyclopropylcarbinols has been realized by lithiation of bromocyclopropyl epoxides with n-butyllithium and subsequent intramolecular attack of the metalated cyclopropane ring onto the epoxide.A series of seven bromoc
- Last, Larry A.,Fretz, E. Robert,Coates, Robert M.
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p. 3211 - 3219
(2007/10/02)
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- Tricyclo2,8>octan-3-one: Photochemisch hergestellte Bausteine zur enantiospezifischen Totalsynthese cyclopentanoider Naturstoffe
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Bi- und tricyclopentanoide Naturstoffe stehen seit einigen Jahren als Zielstrukturen im Vordergrund des Interesses praeparativ arbeitender Chemiker.Mangels abwandelbarer Synthesemethoden wurden bisher meist nur produktbezogene Einzelloesungen erreicht, wobei in der Regel racemische Endstufen erhalten wurden.Das hier vorgestellte neue Konzept geht von einem einfachen Grundbaustein, dem Tricyclo2,8>octan-3-on, aus und erschliesst erstmals einen enantiospezifischen Zugang zu verschiedenen cyclopentanoiden Verbindungen.Das Tricyclooctanon ist in hoher Ausbeute aus Benzol erhaeltlich; dabei ist die Triplett-sensibilisierte Oxa-di-$ p-methan-Umlagerung von Bicyclooctenon die photochemische Schluesselreaktion.Racematspaltungen koennen problemlos auf der Bicyclooctenon-Stufe vorgenommen werden.Die strukturellen Eigenschaften des Tricyclooctanons erfuellen die Anforderungen an einen zentralen Synthesebaustein: Isomerisierungs- und Aufbaureaktionen lassen sich in hohen Ausbeuten regio- und stereoselektiv ausfuehren.Erste abgeschlossene Anwendungsbeispiele, Totalsynthesen von Boschnialacton, Allodolicholacton, Irido- und Isoridomyrmecin sowie von O-Acetyl-loganinaglucon, und erfolgversprechende Ansaetze zur Synthese von Coriolin, von 6a-Carbaprostacyclin und Homologen sowie von 9,11-Dehydrooestron demonstrieren das einzigartige Synthesepotential des Tricyclooctanons fuer Totalsynthesen polycyclopentanoider Verbindungen.
- Demuth, Martin,Schaffner, Kurt
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p. 809 - 825
(2007/10/02)
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