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High Diastereo (high + diastereo)
Selected AbstractsProlylprolinol-Catalyzed Asymmetric Michael Addition of Aliphatic Aldehydes to NitroalkenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010Dengfu Lu Abstract Several novel prolylprolinol catalysts have been designed and synthesized. This type of compound showed high catalytic efficiency on promoting the direct addition of unmodified aldehydes to nitroalkenes. Among the catalysts surveyed, the least bulky member (8d) exhibited the best performance on both efficiency and stereoselectivity, providing the products with up to 97% ee value with 1.5,5,mol% catalyst loading. Additionally, computational studies of the transition state have been conducted to explain the high diastereo- and enantioselectivity. [source] Organocatalyzed Conjugate Addition of Carbonyl Compounds to Nitrodienes/Nitroenynes and Synthetic ApplicationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010Sébastien Belot Abstract The purpose of this study is to point out the synthetic utility of a new class of Michael acceptors (nitrodienes and nitroenynes). The highly enantioselective organocatalytic Michael addition of carbonyl compounds to these functionalized nitroolefins has been carried out in the presence of (S)-diphenylprolinol silyl ether to achieve some interesting building blocks in high selectivities. The adducts thus obtained can be easily converted by taking advantage of the corresponding unsaturated carbon-carbon bond. In presence of the double bond, metathesis or electrophilic activation could be carried out whereas in the presence of the triple bond electrophilic activation could be conducted. We thus focused on a gold-catalyzed cyclization of the bis-homopropargylic alcohol to afford the corresponding substituted tetrahydrofuran. Then, we also demonstrated that organic and gold catalysts were compatible in a one-pot process. Indeed, we developed a one-pot enantioselective organocatalytic Michael addition to a nitroenyne followed by a gold-catalyzed acetalization/cyclization to achieve tetrahydrofuranyl ethers in high diastereo- and enantioselectivities with excellent yields. [source] Highly Enantioselective Organocatalytic syn - and anti -Aldol Reactions in Aqueous MediumADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Monika Raj Abstract We have synthesized chiral diamines that efficiently catalyze the syn - and anti -aldol reactions in aqueous medium with high diastereo- and enantioselectivities. The product, thus obtained, was further reduced selectively to give syn -configured 1,2,3-triol, an important subunit present in various monosaccharides and natural products such as (+)-boronolide. [source] Amine-Catalyzed Asymmetric Epoxidation of ,,,-Unsaturated AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2007Gui-Ling Zhao Abstract The direct organocatalytic enantioselective epoxidation of ,,,-unsaturated aldehydes with different peroxides is presented. Proline, chiral pyrrolidine derivatives, and amino acid-derived imidazolidinones catalyze the asymmetric epoxidation of ,,,-unsaturated aldehydes. In particular, protected commercially available ,,,-diphenyl- and ,,,-di(,-naphthyl)-2-prolinols catalyze the asymmetric epoxidation reactions of ,,,-unsaturated aldehydes with high diastereo- and enantioselectivities to furnish the corresponding 2-epoxy aldehydes in high yield with up to 97:3 dr and 98,% ee. The use of non-toxic catalysts, water and hydrogen peroxide, urea hydroperoxide or sodium percarbonate as the oxygen sources could make this reaction environmentally benign. In addition, one-pot direct organocatalytic asymmetric tandem epoxidation-Wittig reactions are described. The reactions were highly diastereo- and enantioselective and provide a rapid access to 2,4-diepoxy aldehydes. Moreover, a highly stereoselective one-pot organocatalytic asymmetric cascade epoxidation-Mannich reaction, which proceeds via the combination of iminium and enamine activation, is presented. The mechanism and stereochemistry of the amino acid- and chiral pyrrolidine-catalyzed direct asymmetric epoxidation of ,,,-unsaturated aldehydes are also discussed. [source] Aqueous Asymmetric Mukaiyama Aldol Reaction Catalyzed by Chiral Gallium Lewis Acid with Trost-Type Semi-Crown LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Hui-Jing Li Abstract The combination of Ga(OTf)3 with chiral semi-crown ligands (1a,e) generates highly effective chiral gallium Lewis acid catalysts for aqueous asymmetric aldol reactions of aromatic silyl enol ethers with aldehydes. A ligand-acceleration effect was observed. Water is essential for obtaining high diastereoselectivity and enantioselectivity. The p -phenyl substituent in aromatic silyl enol ether (2,h) plays an important role and increases the enantioselectivity up to 95% ee. Although aliphatic silyl enol ethers provided low enantioselectivities and silylketene acetal is easily hydrolyzed in aqueous alcohol, the aldol reactions of silylketene thioacetal (12) with aldehydes in the presence of gallium-Lewis acid catalysts give the ,-hydroxy thioester with reasonable yields and high diastereo- (up to 99,:,1) and enantioselectivities (up to 96% ee). [source] Copper-Catalyzed Diastereo- and Enantioselective Sequential Reactions of Propargylic Acetates with (E)-2,4-PentadienylamineCHEMCATCHEM, Issue 2 2010Gaku Hattori Natural selection: The copper-catalyzed diastereo- and enantioselective sequential reactions of propargylic acetates with (E)-2,4-pentadienylamine give the corresponding 1,2-disubstituted tetrahydroisoindoles in high yields with high diastereo- and enantioselectivities, in which only a single copper works as a catalyst to promote both steps: the propargylic amination and intramolecular [4+2] cycloaddition. [source] Bifunctional-Thiourea-Catalyzed Diastereo- and Enantioselective Aza-Henry ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006Xuenong Xu Dr. Abstract Bifunctional thiourea 1,a catalyzes aza-Henry reaction of nitroalkanes with N -Boc-imines to give syn -,-nitroamines with good to high diastereo- and enantioselectivity. Apart from the catalyst, the reaction requires no additional reagents such as a Lewis acid or a Lewis base. The N-protecting groups of the imines have a determining effect on the chirality of the products, that is, the reaction of N -Boc-imines gives R adducts as major products, whereas the same reaction of N -phosphonoylimines furnishes the corresponding S adducts. Various types of nitroalkanes bearing aryl, alcohol, ether, and ester groups can be used as nucleophiles, providing access to a wide range of useful chiral building blocks in good yield and high enantiomeric excess. Synthetic versatility of the addition products is demonstrated by the transformation to chiral piperidine derivatives such as CP-99,994. [source] | ||||||||||