- Pendant Alkoxy Groups on N-Aryl Substitutions Drive the Efficiency of Imidazolylidene Catalysts for Homoenolate Annulation from Enal and Aldehyde
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Hydrogen-transfer in the tetrahedral intermediate generated from an imidazolylidene catalyst and α,β-unsaturated aldehyde forms a conjugated Breslow intermediate. This is a critical step affecting the efficiency of the NHC-catalyzed γ-butyrolactone formation via homoenolate addition to aryl aldehydes. A novel type of imidazolylidene catalyst with pendant alkoxy groups on the ortho-N-aryl groups is described. Catalyst of this sort facilitates the formation of the conjugated Breslow intermediate. Studies of the rate constants for homoenolate annulation affording γ-butyrolactones, reveal that introduction of the oxygen atoms in the appropriate position of the N-aryl substituents can increase the efficiency of imidazolylidene catalysts. Structural and mechanistic studies revealed that pendant alkoxy groups can be located close to the proton of the tetrahedral intermediate, thereby facilitating the proton transfer.
- Kyan, Ryuji,Mase, Nobuyuki,Narumi, Tetsuo,Sato, Kohei
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p. 19031 - 19036
(2020/08/25)
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- Twist does a twist to the reactivity: Stoichiometric and catalytic oxidations with twisted tetramethyl-IBX
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The methyl groups in TetMe-IBX lower the activation energy corresponding to the rate-determining hypervalent twisting (theoretical calculations), and the steric relay between successive methyl groups twists the structure, which manifests in significant solubility in common organic solvents. Consequently, oxidations of alcohols and sulfides occur at room temperature in common organic solvents. In situ generation of the reactive TetMe-IBX from its precursor iodo-acid, i.e., 3,4,5,6-tetramethyl-2-iodobenzoic acid, in the presence of oxone as a co-oxidant facilitates the oxidation of diverse alcohols at room temperature.
- Moorthy, Jarugu Narasimha,Senapati, Kalyan,Parida, Keshaba Nanda,Jhulki, Samik,Sooraj, Kunnikuruvan,Nair, Nisanth N.
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experimental part
p. 9593 - 9601
(2012/01/03)
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- Thermal decomposition modes for four-coordinate ruthenium phosphonium alkylidene olefin metathesis catalysts
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The four-coordinate ruthenium phosphonium alkylidenes 1-Cy and 1-iPr, differing in the substituent on the phosphorus center, were observed to decompose thermally in the presence of 1,1-dichloroethylene to produce [H 3CPR3][Cl]. The m
- Leitao, Erin M.,Dubberley, Stuart R.,Piers, Warren E.,Wu, Qiao,McDonald, Robert
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supporting information; experimental part
p. 11565 - 11572
(2009/12/07)
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- Syntheses, Enrichment of Enantiomers, and Barriers to Racemization of Twisted 9,10-Phenanthrenquinones
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The known syntheses of the 9,10-phenanthrenequinones 10a-c were improved by the chlorotrimethylsilane modification of the acyloin condensation of biaryl diesters.The novel quinones 4a, 4b, and 12 were prepared.For the first time, enantiomers (M and P) of this class of compounds were enriched semipreparatively by liquid chromatography on optically active sorbents.The barriers to thermal racemization amount to 90-130 kJ mol-1 (Table 2) and are thus higher than the barriers for the corresponding phenanthrene hydrocarbons by roughly 20 kJ mol -1.The reasons for this increase are discussed in terms of repulsive interactions in the trans ition state of helix inversion.
- Fritsch, Rainer,Hartmann, Erwin,Andert, Doris,Mannschreck, Albrecht
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p. 849 - 856
(2007/10/02)
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