- Selective Pinacol Coupling on Regeneratable Supported Acids in Sole Water
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Efficient pinacol coupling was developed in sole water, using a reusable heterogeneous supported acid source and zinc as cheap available metal source. This medium can be easily regenerated up to 10-fold without loss of activity. Moreover, supported acids enhance the selectivity of the pinacol coupling reaction compared with homogeneous acids.
- Sotto, Nicolas,Billamboz, Muriel,Chevrin-Villette, Carole,Len, Christophe
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p. 6375 - 6380
(2015/06/30)
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- Catalytic enantioselective allylation of dienals through the intermediacy of unsaturated π-allyl complexes
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(Chemical Equation Presented) The nickel-catalyzed enantioselective addition of allylboronic acid pinacol ester [allylB(pin)] to >,β,γ,δ-unsaturated aldehydes is described. This reaction results in a remarkable inversion of substrate olefin geometry, providing the Z,E-configured reaction product in good enantioselectivity and olefin stereoselectivity. The reaction appears to proceed by conversion of the dienal to an unsaturated B-allyl complex followed by reductive elimination via transition state II. Enantioselectivities range from 73-94% ee for a range of δ-substituted dienals when chiral ligand L3 is employed.
- Zhang, Ping,Morken, James P.
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supporting information; scheme or table
p. 12550 - 12551
(2010/01/30)
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- Aggregation behavior of tetraenoic fatty acids in aqueous solution
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(Chemical Equation Presented) Why so blue? Unique blue-shifted UV absorptions were used to follow the aggregation of C24 tetraene fatty acids in aqueous solution. Aggregation takes place through three distinct states (i.e. K→T1→T2; see picture). It is suggested that all of these aggregates are lamellar-type in a local sense but differ in the packing mode of the fatty acid backbone.
- Wang, Yonghui,Ma, Jianguo,Cheon, Hwan-Sung,Kishi, Yoshito
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p. 1333 - 1336
(2008/04/05)
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- Carbenoid pathways in copper-catalyzed intramolecular cyclopropanations of phenyliodonium ylides
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The enantioselectivity of the copper-catalyzed intramolecular cyclopropanation of allyl diazomalonates and the corresponding phenyliodonium ylides was investigated with a series of chiral, non-racemic ligands. The reaction of 6b in the presence of the bis[dihydrooxazole] ligand Xa in refluxing 1,2-dichloroethane proceeded to 8b with an enantiomer excess (ee) of up to 72% under optimized conditions. In contrast, 8b resulting from reaction of ylide 7b with the same ligand, but in CH2Cl2 at 0°, had an ee of only 30%. With other ligands, diazomalonate 6b reacted with a lower enantioselectivity than ylide 7b, however. The intramolecular cyclopropanation of the acetoacetate-derived phenyliodonium ylide 15b afforded 16b with 68% ee with ligand Xa, but the corresponding diazo compound was unreactive when exposed to chiral copper catalysts. The observation of asymmetric induction in the Cu-catalyzed reactions of the ylides 7 and 15 is consistent with a carbenoid mechanism however, the discrepancy of the enantioselectivities observed between diazomalonate 6b and ylide 7b suggests a competing unselective pathway for cyclopropanation outside of the coordination sphere of copper.
- Mueller, Paul,Bolea, Christelle
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p. 1093 - 1111
(2007/10/03)
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- COMPOUNDS WITH A HERBAL ODOR III. CIS-ALKENES WITH AN OXYGEN FUNCTION AT THE β POSITION AND THEIR SYNTHESIS BY HYDROGENATION OF DIENE PRECURSORS AT CHROMIUM HEXACARBONYL
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During the hydrogenation of dienes with oxygen functions at the α position in the presence of chromium hexacarbonyl 1,4-addition of hydrogen to the diene system occurs, and this leads to the corresponding cis-monoene derivatives.In the case of dienes with hydroxyl, alkoxyl, acetal, and ester groups the product yield approaches quantitative; the hydrogenation of similar oxo and acyloxy derivatives is less satisfactory.Many representatives of the synthesized compounds, in which the cis-disubstituted double bond is separated from the oxygen-containing functional group by two carbon atoms, have a herbal odor.
- Vasil'ev, A. A.,Cherkaev, G. V.
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p. 834 - 840
(2007/10/02)
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- Total Synthesis of Frustulosin and Aurocitrin
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The regioselective total syntheses of the novel fungal antibiotics frustulosin (1) and aurocitrin (2) were accomplished from 3,6-dihydroxy-2-iodobenzaldehyde (10) which was prepared by a regiodirected metalation of 2,5-dimethylbenzyl vinyl ether to establish the 1,2,3,4-tetrasubstitution pattern of these compounds.The unsaturated side chains of these hydroquinone antibiotics were attached by using the iodo aldehyde functionalities.The structures of these antibiotics are confirmed by synthesis.
- Ronald, Robert C.,Lansinger, Janet M.,Lillie, Thomas S.,Wheeler, Carl J.
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p. 2541 - 2549
(2007/10/02)
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- Structural Dynamics of Pentadienyl Metal-Compounds Bearing a Terminal Alkyl Substituent: Both 'Stereoselective' and 'Stereodefensive' Synthesis of a Natural Perfume
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The (2Z,4E)-, (2E,4Z)- and (2E,4E)-isomers of 2,4-decandien-1-ol (5) have been obtained with high and predictable stereochemical homogeneity starting from both (Z)- and (E)-1,4-decadiene.These hydrocarbons were hydroxylated in a reaction sequence consisting of metallation (by means of s-butyllithium or butyllithium/potassium-t-butoxide, giving rise to organometallic intermediates of specific conformations), dimethoxyborylation and oxidation.The different decadienols as well as (2E,4Z)-2,4-undecadien-1-ol were converted into the isovalerates, the ester derived from (2E,4Z)-2,4-decadien-1-ol being a natural flavor component.
- Bosshardt, Herbert,Schlosser, Manfred
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p. 2393 - 2403
(2007/10/02)
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