- Studies of the Electronic Effects of Zinc Cluster Catalysts and Their Application to the Transesterification of β-Keto Esters
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The electronic effects of tetranuclear zinc cluster catalysts on transesterification were investigated by changing the carboxylate ligands in the clusters. High catalyst activity crucially depended on the balance between Lewis acidity and Br?nsted basicity of the catalyst; this was consistent with the dual activation of both the electrophile and nucleophile by the cooperative zinc centers. In addition, tetranuclear zinc cluster catalysts achieved the transesterification of β-keto esters with unprecedented levels of broad substrate generality, in which a newly developed pentafluoropropionate-bridged zinc cluster and 4-dimethylaminopyridine additive greatly improved the reactivity of sterically congested α- and α,α-disubstituted β-keto esters. Lewis versus Br?nsted: High catalyst activity of zinc clusters on transesterification crucially depend on a balance between Lewis acidity and Br?nsted basicity of the catalyst. Zinc clusters, including a newly developed pentafluoropropionate-bridged zinc cluster, achieved the transesterification of β-keto esters with unprecedented levels of broad substrate generality (see figure).
- Agura, Kazushi,Hayashi, Yukiko,Wada, Mari,Nakatake, Daiki,Mashima, Kazushi,Ohshima, Takashi
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supporting information
p. 1548 - 1554
(2016/06/01)
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- Borrowing hydrogen: Iridium-catalysed reactions for the formation of C-C bonds from alcohols
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Alcohols have been employed as substrates for C-C bond-forming reactions which involve initial activation by the temporary removal of hydrogen to form an aldehyde. The intermediate aldehyde is converted into an alkene via a Horner-Wadsworth-Emmons reaction, nitroaldol and aldol reactions. The 'borrowed hydrogen' is then returned to the alkene to form a C-C bond. The Royal Society of Chemistry 2006.
- Black, Phillip. J.,Cami-Kobeci, Gerta,Edwards, Michael G.,Slatford, Paul A.,Whittlesey, Michael K.,Williams, Jonathan M. J.
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p. 116 - 125
(2007/10/03)
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- Intramolecular cyclopropanation reactions en route to novel P- heterocycles
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The first examples of intramolecular cyclopropanation reactions on a phosphonate template catalyzed by Rh2(OAc)4 are described. These reactions proceed in excellent yield and give mixtures of the P-heterocycles cis-2a-d and trans-2a-d with moderate levels of diastereoselectivity. The diastereoselectivity of this transformation is dependent upon the size of the alkyl group R contained in the alkyl α-diazodiallylphosphonoacetate starting materials 1a-d.
- Hanson, Paul R.,Sprott, Kevin T.,Wrobleski, Aaron D.
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p. 1455 - 1458
(2007/10/03)
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- Efficient stereoselective synthesis of the epoxyacid fragment of the azinomycins
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Three concise enantioselective synthetic routes to the C17-C21 epoxyacid segment of the azinomycins are presented and were based on a Sharpless asymmetric epoxidation/kinetic resolution of racemic allylic alcohol (±)-3 that occurred with reversal of the expected sense of enantioselection.
- Coleman, Robert S.,Sarko, Christopher R.,Gittinger, Jens P.
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p. 5917 - 5920
(2007/10/03)
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- EFFICIENT ESTER EXCHANGE REACTION OF PHOSPHONOACETATES
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A novel method for the preparation of differentially substituted phosphonoacetates and phosphonoacetamides using 4-DMAP catalyzed ester exchange reaction has been developed.
- Hatakeyama, Susumi,Satoh, Kumiko,Sakurai, Kuniya,Takano, Seiichi
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p. 2713 - 2716
(2007/10/02)
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