- ReBr(CO)5-catalyzed sequential addition-cyclization of 1,3-dicarbonyl compounds with electron-deficient internal alkynes affording trisubstituted 2H-pyran-2-ones
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The reaction of 1,3-dicarbonyl compounds such as acetoacetate, acetylacetone, dibenzoylmethane, and benzoylacetate with electron-deficient internal alkynes in the presence of catalytic amount of ReBr(CO)5 in toluene under neutral conditions resulted in the formation of 4,5,6-trisubstituted 2H-pyran-2-ones in moderate to high yield. The reaction took place via a two-step sequence including the rhenium(I)-catalyzed addition of the activated methylenes to alkynes to give enolic 2-alkenyl derivatives, and subsequently dealcoholic cyclization to form 2H-pyran-2-one derivatives.
- Zhao, Wen-Guo,Hua, Ruimao
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- A convenient procedure for the synthesis of 4,6-disubstituted 2-oxo-2H-pyran-5-carboxylic esters
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A simple procedure for the synthesis of 2H-pyran-2-ones 2a is described: The initial Michael addition product of β-ketoester anions with acetylenic esters readily cyclizes under the basic reaction conditions to give the α-pyrones 2a (Scheme 2).
- Covarrubias-Zuniga, Adrian,Maldonado, Luis A.,Diaz-Dominguez, Jose
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p. 1530 - 1538
(2007/10/03)
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- Studies on Metabolites of Macrophoma commelinae. IV. Substrate Specificity in the Biotransformation of 2-Pyrones to Substituted Benzoic Acids
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Substrate specificity in the novel biotransformation from 2-pyrone derivatives to substituted benzoic acids by Macrophoma commelinae (IFO 9570) was investigated by means of feeding experiments with various compounds.Among them, 2-pyrone derivatives substituted by an electron-donating group at C-4, by an electron-withdrawing group at C-5 and by an alkyl group at C-6 were converted to the corresponding benzoic acid derivatives in fairly good yields.The C3-unit precursors and intermediates were examined in stationary or shaking culture.Based on the experimental results obtained, a mechanism for this unique reaction is proposed. macrophoma commelinae IFO 9570; fungi; 2-pyrone; substituted benzoic acid; biotransformation; substrate specificity; aromatic ring formation; macrophomic acid
- Sakurai, Ikuo,Miyajima, Hisae,Akiyama, Katsuyoshi,Shimizu, Sakae,Yamamoto, Yuzuru
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p. 2003 - 2011
(2007/10/02)
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- Synthetic Approach to Aklavinone Using 2-Oxo-2H-pyran-5-carboxylate (Coumalate) Intermediates
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A novel approach for the preparation of aklavinone 5 is described in which the key step is the cycloaddition of a substituted coumalate with a ketene acetal to produce a masked A ring with the C and D rings attached.The 4-(arylmethyl)coumalate 53 was prepared from naphthalene-1,5-diol (6) by a seven step route involving as the key step the cyclocondensation of the methyl (arylmethyl)propiolate 52 with methyl 3-oxopentanoate 10.Cycloaddition of 53 with dimethyl ketene acetal 12 produced the potential A-ring precursor 67, which could not be cleanly reduced, thereby ending this scheme.The preparation of functionalized 4,6-dialkylpyrone-5-carboxylates and their use in the synthesis of bicyclic lactones and substituted benzoates via cycloaddition reactions are also described.
- Jung, Michael E.,Hagenah, Jeffrey A.
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p. 1889 - 1902
(2007/10/02)
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