- Pd(II)-catalyzed sequential C-C/C-O bond formations: A new strategy to construct trisubstituted furans
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Palladium-catalyzed oxidative difunctionalization of enol ethers with 1,3-dicarbonyl compounds to construct trisubstituted furans in one step under mild conditions is described. The reaction is thought to proceed through a C-C bond formation along with a C-O bond closing the ring structure. Oxygen is the sole oxidant regenerating the Pd(II) catalyst.
- Zheng, Meifang,Huang, Liangbin,Wu, Wanqing,Jiang, Huanfeng
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p. 1838 - 1841
(2013/06/04)
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- Oxidative deprotection of silylethers, acetals and ketals by oxygen or air in presence of manganese and cobalt salts of 4-aminobenzoic acid supported on silica gel as catalyst
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Oxidative deprotection of silylethers, acetals and ketals, to their corresponding alcohols, aldehydes and ketones have been achieved using oxygen or air in the presence of cobalt and manganese salts of 4-aminobenzoic acid supported an silica gel as catalysts. Reactions are clean and catalysts can be recovered easily and reused repeatedly.
- Hashemi, Mohammed M.,Kalantari, Fariba
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p. 1857 - 1863
(2007/10/03)
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- Enolization of aldehydes and ketones: Structural effects on concerted acid-base catalysis
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The third-order term (k(AB)) for the concerted acid-base catalyzed enolization of a selection of simple aldehydes and ketones has been measured in a series of substituted acetic acids at 25°C at constant ionic strength 2.0 (NaNO3). While there is no direct correlation of the magnitude of the third-order term with either the rate constants for acid (k(A)) or base (k(B)) catalysis, a simple log-log relationship exists between the product of the consecutive rate constants (k(A)·k(B)) and the concerted (third order) rate constants (k(AB)). This implies that the concerted pathway is important only when both the general acid and the general base terms are significant; this will be useful in designing other systems which might show such concerted catalysis. In the case of aldehydes, a slope of 0.97 was found for this plot, which compares to the result for 4-substituted cyclohexanones (0.51) and other ketones (0.59), as measured in acetic acid buffers. The resultant Bronsted β(AB) value of 0.20 found for propanal (2) is consistent with the overall observation that concerted catalysis is largely independent of the buffering species, and that process is overall base catalyzed. The solvent isotope effect on the concerted acid-base catalyzed enolization rate term, k(AB)(H2O)/k(AB)(D2O) = 1.33, indicates that the transition state for proton transfer to the carbonyl is more advanced than in the case of ketones. In general we have found that carbonyl compounds with large measured (or estimated) enol contents show significant third-order terms.
- Hegarty, Anthony F.,Dowling, Joseph P.,Eustace, Stephen J.,McGarraghy, Michelle
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p. 2290 - 2296
(2007/10/03)
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- Mechanistic Change in Acid-Catalyzed Hydrolysis of Silyl Vinyl Ethers
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tert-Butyldimethylsilyl vinyl ethers t-BuMe2SiOCR=CH2 hydrolyze in 50percent CH3CN - H2O with general and specific acid catalysis and a linear dependence of log kH+ on ?p+(R), indicating that the reaction occurs with rate-determing proton transfer to carbon (the ADE2 mechanism).By contrast the rates of trimethylsilyl vinyl ethers Me3SiOCR=CH2 are not correlated by ?p+(R) but still depend on proton and general acid concentrations.Nucleophilic attack on silicon is implicated in the rate-determing step of the latter compounds, and the possibilities for the details of this process are considered.
- Novice, Marilyn H.,Seikaly, Hani R.,Seiz, Annette D.,Tidwell, Thomas T.
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p. 5835 - 5838
(2007/10/02)
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