- Asymmetric Kulinkovich Hydroxycyclopropanation of Alkenes Mediated by Titanium(IV) TADDOLate Complexes
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Asymmetric Kulinkovich cyclopropanation of carboxylic esters with prochiral alkenes is reported. The process is mediated by titanium(IV) (4 R,5 R)-TADDOLate complexes and affords correspondingly (Z)- or (E)-cyclopropanols with up to 84-87% ee in the event of intra- or intermolecular olefin ligand exchange in intermediate titanacyclopropane [titanium(II)-alkene] species. Configuration of the olefin double bond is preserved in the cyclopropane products, pointing out on total retention of configuration at Ti-C bond in the cyclopropane forming step. The results have been interpreted in the framework of ate complex mechanism, suggesting formation of pentacoordinated titanium ate species as a prerequisite of high enantiocontrol.
- Iskryk, Marharyta,Barysevich, Maryia,O?eka, Maksim,Adamson, Jasper,Kananovich, Dzmitry
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- Tropolonate salts as acyl-transfer catalysts under thermal and photochemical conditions: Reaction scope and mechanistic insights
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Acyl-transfer catalysis is a frequently used tool to promote the formation of carboxylic acid derivatives, which are important synthetic precursors and target compounds in organic synthesis. However, there have been only a few structural motifs known to efficiently catalyze the acyl-transfer reaction. Herein, we introduce a different acyl-transfer catalytic paradigm based on the tropolone framework. We show that tropolonate salts, due to their strong nucleophilicity and photochemical activity, can promote the coupling reaction between alcohols and carboxylic acid anhydrides or chlorides to give products under thermal or blue light photochemical conditions. Kinetic studies and density functional theory calculations suggest interesting mechanistic insights for reactions promoted by this acyl-transfer catalytic system.
- Mai, Binh Khanh,Koenigs, Rene M.,Nguyen, Thanh Vinh,Lyons, Demelza J.M.,Empel, Claire,Pace, Domenic P.,Dinh, An H.
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p. 12596 - 12606
(2020/11/18)
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- TEMPO-Catalyzed Oxidative Amidation of Alcohols via Hexafluoroisopropyl Esters
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Stepwise oxidative amidation of alcohols using trichloroisocyanuric acid, a catalytic amount of TEMPO in combination with pyridine and hexafluoroisopropyl (HFIP) alcohol followed by amines is described. This procedure used HFIP esters as activating esters which were found to be very efficient acylating agents for amide bond formation. This process is compatible with a number of functional groups and acid-sensitive protecting groups.
- Vatèle, Jean-Michel
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supporting information
p. 2280 - 2284
(2015/09/28)
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- Unprecedented iron-catalyzed ester hydrogenation. Mild, selective, and efficient hydrogenation of trifluoroacetic esters to alcohols catalyzed by an iron pincer complex
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The synthetically important, environmentally benign hydrogenation of esters to alcohols has been accomplished in recent years only with precious-metal-based catalysts. Here we present the first iron-catalyzed hydrogenation of esters to the corresponding alcohols, proceeding selectively and efficiently in the presence of an iron pincer catalyst under remarkably mild conditions. The replacement of precious-metal catalysts by an iron complex was accomplished for the synthetically important, environmentally benign hydrogenation of esters to alcohols under mild conditions. The iron pincer complex (see scheme) selectively and efficiently catalyzes the hydrogenation of trifluoroacetates under remarkably mild conditions (5-25 bar and 40 °C).
- Zell, Thomas,Ben-David, Yehoshoa,Milstein, David
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supporting information
p. 4685 - 4689
(2014/05/20)
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- Aerobic oxidation of NHC-catalysed aldehyde esterifications with alcohols: Benzoin, not the Breslow intermediate, undergoes oxidation
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Benzoin (and neither the Breslow intermediate nor the NHC-aldehyde tetrahedral adduct) has been unambiguously identified as the oxidised species in aerobic NHC-catalysed aldehyde esterifications.
- Delany, Eoghan G.,Fagan, Claire-Louise,Gundala, Sivaji,Zeitler, Kirsten,Connon, Stephen J.
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p. 6513 - 6515
(2013/07/26)
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- Competing SN2 and Carbonyl Addition Pathways for Solvolyses of Benzoyl Chloride in Aqueous Media
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The further development of a convenient, conductimetric method for studying the rates of relatively fast solvolytic reactions in highly aqueous media is described.Rate and product data are reported for solvolyses of benzoyl chloride at 25 deg C in water and in binary aqueous mixtures with acetone, ethanol, methanol, trifluoroethanol, and hexafluoropropan-2-ol.Comparison of these kinetic data with rate data for the SN1 model, 1-adamantyl chloride, reveals sensitivity to solvent nucleophilicity even for highly aqueous media.In constrast with other nucleophilically solvent-assisted processes, the solvent effects are not satisfactorily correlated by one linear free energy relationship.Gas-phase thermochemical data show the feasibility of a direct heterolytic cleavage of the C-Cl bond in benzoyl chloride.Rate-product correlations for hydrolysis and aminolysis in 50percent w/w acetone-water are observed, providing that allowance is made for the medium effect of the added o-nitroaniline.These results are consistent with an SN2 mechanism, not SN1 and/or ion-pair mechanisms previously discussed.Another pathway, dominant in less aqueous media, is much less sensitive to changes in solvent ionizing power, consistent with earlier proposals for a carbonyl addition-elimination mechanism.
- Bentley, T. William,Carter, Gillian E.,Harris, H. Carl
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p. 983 - 990
(2007/10/02)
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