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Quaternary Stereocenter (quaternary + stereocenter)
Selected AbstractsSynthesis of an Optically Active Decahydro-6-isoquinolone Scaffold with a Quaternary StereocenterEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2004Jens Christoffers Abstract A straightforward synthesis of optically active decahydro-6-isoquinolone derivative 3, containing a quaternary stereocenter, is reported. The starting (R)-configured enantiopure enone 2, which is readily accessible through a copper-catalyzed, L -valine amide mediated Michael reaction and a subsequent Robinson annulation, was hydrogenated with Pd/C in iPrOH to give the decahydroisoquinolone 4. Treatment of 4 with ethyleneglycol in the presence of PPTS yielded the dioxolane-protected derivative 7. A sequence of ester reduction with LiAlH4 and subsequent Ley oxidation of the resulting primary alcohol 10 accomplished the synthesis. Enantiomerically pure aldehyde 3, with three groups for further functionalization, was thus obtained in 63% overall yield. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Total Synthesis of LFA-1 Antagonist BIRT-377 via Organocatalytic Asymmetric Construction of a Quaternary Stereocenter.CHEMINFORM, Issue 29 2005Naidu S. Chowdari Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of an Optically Active Decahydro-6-isoquinolone Scaffold with a Quaternary StereocenterEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2004Jens Christoffers Abstract A straightforward synthesis of optically active decahydro-6-isoquinolone derivative 3, containing a quaternary stereocenter, is reported. The starting (R)-configured enantiopure enone 2, which is readily accessible through a copper-catalyzed, L -valine amide mediated Michael reaction and a subsequent Robinson annulation, was hydrogenated with Pd/C in iPrOH to give the decahydroisoquinolone 4. Treatment of 4 with ethyleneglycol in the presence of PPTS yielded the dioxolane-protected derivative 7. A sequence of ester reduction with LiAlH4 and subsequent Ley oxidation of the resulting primary alcohol 10 accomplished the synthesis. Enantiomerically pure aldehyde 3, with three groups for further functionalization, was thus obtained in 63% overall yield. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A Direct Intermolecular Cross-Benzoin Type Reaction: N-Heterocyclic Carbene-Catalyzed Coupling of Aromatic Aldehydes with Trifluoromethyl KetonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Dieter Enders Abstract A direct intermolecular cross-benzoin-type condensation catalyzed by an N-heterocyclic carbene has been developed. The cross-coupling of commercially available aromatic aldehydes and trifluoromethyl ketones results in ,-hydroxy-,-trifluoromethyl ketones bearing a quaternary stereocenter with excellent chemoselectivity and good to excellent yields. [source] Enantioselective Organocatalytic Michael Addition of ,-Substituted Cyanoacetates to ,,,-Unsaturated SelenonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Francesca Marini Abstract A novel enantioselective (up to 90% ee) Michael addition of ,-substituted cyanoacetates to ,,,-unsaturated selenones in the presence of bifunctional urea and thiourea organocatalysts is described. The Michael adducts, containing an all-carbon quaternary stereocenter, are smoothly converted into synthetically useful polyfunctional compounds by taking advantage of the excellent leaving group ability of the selenone group. [source] Catalytic Asymmetric Synthesis of 3-(,-Hydroxy-,-carbonyl) Oxindoles by a ScIII -Catalyzed Direct Aldol-Type ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2010Ke Shen Abstract A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N, -dioxide,Sc(OTf)3 (Tf=trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93,% yield, 99:1 diastereomeric ratio (dr), and >99,% enantiomeric excess (ee)) under mild conditions, to deliver 3-(,-hydroxy-,-carbonyl) oxindoles with vicinal quaternary,tertiary or quaternary,quaternary stereocenters. Even with 1,mol,% catalyst loading or on scaleup (10,mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and ScIII -based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed. [source] | ||||||||||