- A synthetic model for the [4+2] cycloaddition in the biosynthesis of the brevianamides, paraherquamides, and related compounds
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The reactivity of model systems for the proposed [4+2] cycloaddition in the biosynthesis of the brevianamides, paraherquamides, and marcfortines is explored. The model for the intermolecular reaction reveals that the cycloaddition takes place under mild conditions only if activated, very reactive dienophiles are used. When relatively unreactive dienophiles such as cyclopentene and cyclohexene are used, harsh reaction conditions and/or a Lewis acid catalyst are necessary for the reaction. In contrast, the model for the intramolecular reaction demonstrates that the cycloaddition takes place within a few hours at room temperature, even in the absence of a Lewis acid catalyst. Conclusions drawn from these results are discussed in relation to the biosynthesis of the aforementioned metabolites. (C) 2000 Elsevier Science Ltd.
- Sanz-Cervera, Juan F.,Williams, Robert M.,Alberto Marco,María López-Sánchez, José,González, Florenci,Eugenia Martínez, María,Sancenón, Félix
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p. 6345 - 6358
(2007/10/03)
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- Asymmetric Catalytic Hydrogenations of N-Pyruvoyl-(S)-proline Esters
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Asymmetric catalytic hydrogenations of the entitled compounds were carried out over palladium on charcoal in various solvents to afford N--(S)-proline esters with a d.e.(=diastereoisomeric excess) of up to 59percent.The stereochemistry of the catalytic hydrogenation was explained by the "chelation mechanism." And the effects of temperature and bulkiness of the ester groups on the asymmetric induction were also described.
- Munegumi, Toratane,Fujita, Manabu,Maruyama, Tetsuya,Shiono, Shozo,Takasaki, Michiaki,Harada, Kaoru
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p. 249 - 254
(2007/10/02)
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