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High Chemical Yields (high + chemical_yield)
Selected AbstractsHighly Efficient and Practical Pyrrolidine,Camphor-Derived Organocatalysts for the Direct ,-Amination of AldehydesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 29 2010Pang-Min Liu Abstract A series of pyrrolidine,camphor-derived organocatalysts (1,4) were designed and synthesised. These organocatalysts were used for direct ,-amination of aldehydes with dialkyl azodicarboxylates to give the desired ,-aminated products in high chemical yields (up to 92,%) and with high to excellent levels of stereoselectivity (up to >99,% ee). The reactions proceeded rapidly (within 5 min) with low catalyst loading (5 mol-%) at ambient temperature. Enantioselective aminations of asymmetric ,,,-disubstituted aldehydes in the catalytic system were studied, with reasonable to high stereoselectivities (up to 75,% ee) being obtained. The utility of this methodology was demonstrated with the synthesis of derivatives of ,-amino-,-butyrolactone and a tetrasubstitutedcyclohexane-derived amino alcohol with high stereoselectivities. Transition models were proposed for the asymmetric ,-amination reactions; they involve hydrogen-bond interactions between the nucleophilic enamine formed in situ and the nitrogen source. [source] Highly Enantioselective Conjugate Addition of Ketones to Alkylidene Malonates Catalyzed by a Pyrrolidinyl,Camphor-Derived OrganocatalystEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2010Dhananjay R. Magar Abstract Pyrrolidinyl,camphor derivatives have been proven to be efficient organocatalysts for enantioselective conjugate addition of ketones to alkylidene malonates, affording high chemical yields (up to 95,%) of the corresponding products with high to excellent levels of diastereoselectivity (up to >99:1,dr) and enantioselectivity (up to 96,%,ee) under solvent-free reaction conditions at ambient temperature. [source] Gold-Catalyzed Cycloisomerization of ,-Aminoallenes to 3-Pyrrolines ,Optimization and Mechanistic Studies,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2006Nobuyoshi Morita Abstract The gold-catalyzed cycloisomerization of various ,-aminoallenes affords the corresponding 3-pyrrolines in good to high chemical yields and , if the amino group is unprotected , with complete axis-to-center chirality transfer. Diminished levels of chirality transfer were observed in cases of N -protected substrates, which may be the result of partial epimerization of the allene in the presence of the gold precatalyst. The low reactivity of the intramolecular hydroamination of unprotected ,-aminoallenes with AuCl3 was improved by use of gold(I) halides as the precatalyst. Mechanistic studies suggest that a gold(I) compound (formed by oxidation of the aminoallene) is the catalytically active species even if the reaction is started with a gold(III) precatalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Pyrrolidine-Camphor Derivative as an Organocatalyst for Asymmetic Michael Additions of ,,,-Disubstituted Aldehydes to ,-Nitroalkenes: Construction of Quaternary Carbon-Bearing Aldehydes under Solvent-Free ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Chihliang Chang Abstract A novel pyrrolidine-camphor organocatalyst 3 was designed, synthesized and proven to be an efficient catalyst for the asymmetric Michael reaction. Treatment of ,,,-disubstituted aldehydes with ,-nitroalkenes in the presence of 20,mol% organocatalyst 3 and 20,mol% benzoic acid under solvent-free conditions provided the desired Michael product possessing an all-carbon quaternary center with high chemical yields (up to 99% yield) and high levels of enantioselectivities (up to 95% ee). [source] An Efficient and Convenient Synthesis of Ethyl 1-(4-Methoxyphenyl)-5-phenyl-1H -1,2,3-triazole-4-carboxylateCHEMISTRY - AN ASIAN JOURNAL, Issue 2 2010Jung-Hsuan Chen Abstract The "click chemistry" of using organic azides and terminal alkynes is arguably the most efficient and straightforward route to the synthesis of 1,2,3-triazoles. In this paper, an alternative and direct access to ethyl 1-(4-methoxyphenyl)-5-phenyl-1H -1,2,3-triazole-4-carboxylate is described. Treatment of ethyl diazoacetate with 4-methoxyaniline derived aryl imines in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene provided fully substituted 1,2,3-triazoles in good to high chemical yields. The base-mediated reaction tolerates various substituted phenyl imines as well as ethyl diazoacetate or the more bulky diazoacetamide. A reasonable mechanism is proposed that involves the addition of an imine nitrogen atom to the terminal nitrogen atom of the diazo compound, followed by aromatization to give the 1,2,3-triazole. The presence of the 4-carboxy group is advantageous as it can be easily transformed into other functional groups. [source] | ||||||||||