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ABSTRACT: Polysubstituted 5- and 6-membered carbocycles were synthesized by the title reaction. The one-pot dynamic relay process generates four new stereocenters, including a quaternary carbon center, in a highly enantioselective fashion (99.5:0.5→99:0.5 e.r.) by using a simple combination of palladium and chiral amine co-catalysts.
Angewandte Chemie International Edition 04/2013; · 13.45 Impact Factor
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ABSTRACT: A combination of palladium and a simple chiral amine is used as co-catalysts for the enantioselective conjugate addition of aryl boronic acids to α,β-unsaturated aldehydes. The synthetic utility of this co-catalyzed reaction was demonstrated in the short total syntheses of (R)-(-)-curcumene and 4-aryl-2-ones.
Angewandte Chemie International Edition 11/2012; · 13.45 Impact Factor
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ABSTRACT: A stereochemical divergent approach for the highly enantioselective synthesis of distinct bicy-clic products with multiple stereocenters from a racemate using a single chiral catalyst is disclosed. It is based on switches of the overall reaction path-ways in the chiral amine-catalyzed cascade reac-tions between racemic g-nitro ketones and a,b-un-saturated aldehydes using different achiral co-cata-lysts. The utility of the method is exemplified by the highly diasteroselective switch and stereocon-vergent deracemization process by combination of chiral amine and achiral hydrogen-bond-donating catalysts.
Advanced Synthesis & Catalysis 10/2012; 354(14-15):2865-2872. · 6.05 Impact Factor
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ABSTRACT: Metal-free selectivity: The first metal-free one-pot three-component highly chemo- and regioselective catalytic synthesis of homoallylboranes using simple N-heterocyclic carbenes (NHC) and amines is presented. The catalytic reaction between B(2) (pin)(2) , α,β-unsaturated aldehydes and 2-(triphenylphosphoranylidene)acetate esters proceeds through a catalytic metal-free β-boration/Wittig cascade sequence.
Chemistry 03/2012; 18(17):5175-9. · 5.93 Impact Factor
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ABSTRACT: The first direct intermolecular regiospecific and highly enantioselective α-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd(0) complexes and simple chiral amines as co-catalysts is disclosed. The co-catalytic asymmetric chemoselective and regiospecific α-allylic alkylation reaction is linked in tandem with in situ reduction to give the corresponding 2-alkyl alcohols with high enantiomeric ratios (up to 98:2 e.r.; e.r.=enantiomeric ratio). It is also an expeditious entry to valuable 2-alkyl substituted hemiacetals, 2-alkyl-butane-1,4-diols, and amines. The concise co-catalytic asymmetric total syntheses of biologically active natural products (e.g., Arundic acid) are disclosed.
Chemistry 03/2012; 18(10):2972-7. · 5.93 Impact Factor
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ABSTRACT: The concept of combining heterogeneous transition metal and amine catalysis for enantioselective cascade reactions has not yet been realized. This is of great advantage since it would allow for the recycling of expensive and non-environmentally friendly transition metals. We disclose that the use of a heterogeneous Pd-catalyst in combination with a simple chiral amine co-catalyst allows for highly enantioselective cascade transformations. The preparative power of this process has been demonstrated in the context of asymmetric cascade Michael/carbocyclization transformations that delivers cyclopentenes bearing an all carbon quaternary stereocenters in high yields with up to 30:1 dr and 99% ee. Moreover, a variety of highly enantioselective cascade hetero-Michael/carbocyclizations were developed for the one-pot synthesis of valuable dihydrofurans and pyrrolidines (up to 98% ee) by using bench-stable heterogeneous Pd and chiral amines as co-catalysts.
Scientific Reports 01/2012; 2:851.
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Angewandte Chemie International Edition 12/2011; 50(50):12036-41. · 13.45 Impact Factor
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ABSTRACT: Branching out! The first co-catalytic enantioselective (up to 98:2 e.r.) β-alkylation of α,β-unsaturated aldehydes by combination of simple chiral amine and copper catalysts provides β-branched aldehydes in a one-pot protocol. The methodology was applied to the short total syntheses of bisabolane sesquiterpenes (S)-(+)-curcumene, (E)-(S)-(+)-3-dehydrocurcumene and (S)-(+)-tumerone.
Chemistry 07/2011; 17(32):8784-8. · 5.93 Impact Factor
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ABSTRACT: The development, scope, and application of the highly enantioselective organocatalytic aziridination of α,β-unsaturated aldehydes is presented. The aminocatalytic azirdination of α,β-unsaturated aldehydes enables the asymmetric formation of β-formyl aziridines with up to >19:1 d.r. and 99% ee. The aminocatalytic aziridination of α-monosubstituted enals gives access to terminal α-substituted-α-formyl aziridines in high yields and up to 99% ee. In the case of the organocatalytic aziridination of disubstituted α,β-unsaturated aldehydes, the transformations were highly diastereo- and enantioselective and give nearly enantiomerically pure β-formyl-functionalized aziridine products (99% ee). A highly enantioselective one-pot cascade sequence based on the combination of asymmetric amine and N-heterocyclic carbene catalysis (AHCC) is also disclosed. This one-pot three-component co-catalytic transformation between α,β-unsaturated aldehydes, hydroxylamine derivatives, and alcohols gives the corresponding N-tert-butoxycarbonyl and N-carbobenzyloxy-protected β-amino acid esters with ee values ranging from 92-99%. The mechanisms and stereochemistry of all these catalytic transformations are also discussed.
Chemistry 07/2011; 17(28):7904-17. · 5.93 Impact Factor
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Angewandte Chemie International Edition 06/2011; 50(33):7624-30. · 13.45 Impact Factor
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Advanced Synthesis & Catalysis 05/2011; 353(7):1096 - 1108. · 6.05 Impact Factor
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Advanced Synthesis & Catalysis 02/2011; 353(2‐3):245 - 252. · 6.05 Impact Factor
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Advanced Synthesis & Catalysis 12/2010; 352(18):3201 - 3207. · 6.05 Impact Factor
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Chemistry 11/2010; 16(47):13930-4. · 5.93 Impact Factor
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Chemistry 11/2010; 16(47):13935-40. · 5.93 Impact Factor
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Advanced Synthesis & Catalysis 08/2010; 352(13):2291 - 2298. · 6.05 Impact Factor
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ABSTRACT: A simple and direct method for derivatization of solid polysaccharides is presented. The novel methodology is based on the combination of organic acid-catalyzed esterification or etherification and photochemical thiol-ene click derivatization of a heterogeneous polysaccharide. The solid cellulose was "organoclick" modified with aryl, alkyl and polyester groups, respectively. The modification allows for a highly modular and metal free surface modification of solid polysaccharides.
Macromolecular Rapid Communications 04/2010; 31(8):740-4. · 4.60 Impact Factor
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ABSTRACT: In natural environments such as atmospheric aerosols, organic compounds coexist with inorganic salts but, until recently, were not thought to interact chemically. We have recently shown that inorganic ammonium ions, NH(4)(+), act as catalysts for acetal formation from glyoxal, a common atmospheric gas. In this work, we report that inorganic ammonium ions, NH(4)(+), and carbonate ions, CO(3)(2-), are also efficient catalysts for the aldol condensation of carbonyl compounds. In the case of NH(4)(+) this was not previously known, and was patented prior to this article. The kinetic results presented in this work show that, for the concentrations of ammonium and carbonate ions present in tropospheric aerosols, the aldol condensation of acetaldehyde and acetone could be as fast as in concentrated sulfuric acid and might compete with their reactions with OH radicals. These catalytic processes could produce significant amounts of polyconjugated, light-absorbing compounds in aerosols, and thus affect their direct forcing on climate. For organic gases with large Henry's law coefficients, these reactions could also result in a significant uptake and in the formation of secondary organic aerosols (SOA). This work reinforces the recent findings that inorganic salts are not inert towards organic compounds in aerosols and shows, in particular, that common ones, such as ammonium and carbonate salts, might even play important roles in their chemical transformations.
Physical Chemistry Chemical Physics 04/2010; 12(15):3864-72. · 3.57 Impact Factor
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ABSTRACT: The first examples of one-pot highly chemo- and enantioselective dynamic kinetic asymmetric transformations (DYKATs) involving alpha,beta-unsaturated aldehydes and propargylated carbon acids are presented. These DYKATs, which proceed by a combination of catalytic iminium activation, enamine activation, and Pd(0)-catalyzed enyne cycloisomerization, give access to functionalized cyclopentenes with up to 99 % ee and can be used for the generation of all-carbon quaternary stereocenters.
Chemistry 02/2010; 16(5):1585-91. · 5.93 Impact Factor
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ABSTRACT: The asymmetric construction of optically active amine compounds is of paramount interest for the chemical industry and academic research. This review describes the use of catalytic asymmetric transformations, such as Mannich-type, Michael, cycloaddition and transfer-hydrogenation reactions using small organic molecules (eg, amino acids, secondary amines, peptides, thioureas and phosphoric acids) as catalysts, for the construction of important compounds for medicinal chemistry that exhibit anticancer, antibiotic or antiviral activity.
Current opinion in drug discovery & development 11/2009; 12(6):824-47. · 4.20 Impact Factor
