- Coupling Reaction of Enol Derivatives with Silyl Ketene Acetals Catalyzed by Gallium Trihalides
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A cross-coupling reaction between enol derivatives and silyl ketene acetals catalyzed by GaBr3took place to give the corresponding α-alkenyl esters. GaBr3showed the most effective catalytic ability, whereas other metal salts such as BF3?OEt2, AlCl3, PdCl2, and lanthanide triflates were not effective. Various types of enol ethers and vinyl carboxylates as enol derivatives are amenable to this coupling. The scope of the reaction with silyl ketene acetals was also broad. We successfully observed an alkylgallium intermediate by using NMR spectroscopy, suggesting a mechanism involving anti-carbogallation among GaBr3, an enol derivative, and a silyl ketene acetal, followed by syn-β-alkoxy elimination from the alkylgallium. Based on kinetic studies, the turnover-limiting step of the reaction using a vinyl ether and a vinyl carboxylate involved syn-β-alkoxy elimination and anti-carbogallation, respectively. Therefore, the leaving group had a significant effect on the progress of the reaction. Theoretical calculations analysis suggest that the moderate Lewis acidity of gallium would contribute to a flexible conformational change of the alkylgallium intermediate and to the cleavage of the carbon?oxygen bond in the β-alkoxy elimination process, which is the turnover-limiting step in the reaction between a vinyl ether and a silyl ketene acetal.
- Nishimoto, Yoshihiro,Kita, Yuji,Ueda, Hiroki,Imaoka, Hiroto,Chiba, Kouji,Yasuda, Makoto,Baba, Akio
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supporting information
p. 11837 - 11845
(2016/08/05)
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- ANALOGS OF DEHYDROPHENYLAHISTINS
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Analogs of dehydrophenylahistins are disclosed as are methods for making such compounds. Compositions and methods for treating various disease conditions including cancer and non-cancer diseases associated with vascular proliferation are also disclosed.
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- ANALOGS OF DEHYDROPHENYLAHISTINS AND THEIR THEAPEUTIC USE
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Compounds represented by the following structure (II) are disclosed: as are methods for making such compounds. Compositions and methods for treating various disease conditions including cancer and non-cancer diseases associated with vascular proliferation are also disclosed.
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- New synthesis of 2-alkyl-4,4-dimethyl-5-halomethylisoxazolidin-3-ones via intramolecular halocyclization of N-alkyl-2,2-dimethyl-3-butenohydroxamic acids
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N-Alkyl-2,2-dimethyl-3-butenohydroxamic acids and their cyclic derivatives were halocyclized by iodine monochloride, N-bromosuccinimide, or N-chlorosuccinimide to afford the corresponding 2-alkyl-4,4-dimethyl-5-halomethylisoxazolidinones and 5-membered ring fused isoxazolidinones in excellent yields.
- Kim, Hyoung Rae,Shin, Seung Il,Park, Hyun Ju,Jeon, Dong Ju,Ryu, Eung K.
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p. 789 - 791
(2007/10/03)
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- Formation of Lactones via a Radical Ring Closure Mechanism
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Suitable alkenoyloxymethyl iodides or selenides are converted into lactones upon treatment with tributyl-stannane or -germane; the reaction involves highly regioselective and stereoselective ring closure of alkenoyloxymethyl radicals (1).
- Beckwith, Athelstan L. J.,Pigou, Paul E.
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- Selective γ- Alkylation of Copper Enolates Derived from α,β-Unsaturated Acids: Factors Affecting Scope and Regio- and Stereoselectivity
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Copper dienolates derived from α,β-unsaturated acids undergo alkylation at the γ-carbon with high regioselectivity.A systematic investigation has been made of several factors that affect the γ-alkylation process of the dienolate derived tiglic acid (1): alterations in the nature of the counterion, in the stoichiometry of cuprous ion, and in the nature of the electrophile.Compared to allylic electrophiles, nonallylic electrophiles react with copper dienolates sluggishly and with little selectivity for the γ-carbon; vinylic epoxides, however, are particularly goodalkylating agents.They undergo allylic transposition and react at the γ-carbon of the dienolate with high selectivity (70-90 percent), generating an allylic unit that forms part of a 1,5-diene skeleton oxygenated at both ends.Tiglic (1) and crotonic (3) acids react with vinylic epoxides to form a 1,5-diene with entirely E stereochemistry at the 2,3 double bond, while senecioic acid (2) forms a 1,5-diene with mostly Z stereochemistry at the 2,3 double bond.Geometry at the 6,7 double bond depends both on the α,β-unsaturated acid used and on the structure of the epoxide.With allylic electrophiles under direct (SN2) attack, stereochemical analysis showed that some isomerization occurs around the 6,7 double bond (derived from the electrophile).Addition of cuprous ion to the lithium dianion of 2-hexenoic acid (17) was found to enhance the regioselectivity of γ alkylation, but a subsequent Michael addition reaction limits the potential of γ alkylation in this system.
- Savu, Patricia M.,Katzenellenbogen, John A.
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p. 239 - 250
(2007/10/02)
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