Showing papers by "Armando Córdova published in 2012"

Direct regiospecific and highly enantioselective intermolecular α-allylic alkylation of aldehydes by a combination of transition-metal and chiral amine catalysts.

Abstract: The first direct intermolecular regiospecific and highly enantioselective a-allylic alkylation of linear aldehydes by a combination of achiral bench-stable Pd0 complexes and simple chiral amines as ...

One‐Pot Three‐Component Highly Selective Synthesis of Homoallylboronates by Using Metal‐Free Catalysis

Abstract: One-Pot Three-Component Highly Selective Synthesis of Homoallylboronates by Using Metal-Free Catalysis

Intergrown New Zeolite Beta Polymorphs with Interconnected 12- Ring Channels Solved by Combining Electron Crystallography and Single-Crystal X‑ray Diffraction

Abstract: Two new polymorphs of zeolite beta, denoted as SU-78A and SU-78B, were synthesized by employing dicyclohexylammonium hydroxides as organic structure-directing agents. The structure was solved by combining transmission electron microscopy and single-crystal X-ray diffraction. SU-78 is an intergrowth of SU-78A and SU-78B and contains interconnected 12-ring channels in three directions. The two polymorphs are built from the same building layer, similar to that for the zeolite beta family. The layer stacking in SU-78, however, is different from those in zeolite beta polymorph A, B, and C, showing new zeolite framework topologies. SU-78 is thermally stable up to 600 °C.

Highly enantioselective cascade transformations by merging heterogeneous transition metal catalysis with asymmetric aminocatalysis.

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.

Highly Enantioselective Cascade Transformations by Merging Heterogeneous Transition Metal Catalysis with Asymmetric

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.

Concise Catalytic Asymmetric Total Synthesis of Biologically Active Tropane Alkaloids

Abstract: A general strategy for the total asymmetric synthesis of valuable tropane alkaloids by catalytic stereoselective transformations is disclosed. The power of this approach is exemplified by the conci ...

One‐Step Catalytic Enantioselective α‐Quaternary 5‐Hydroxyproline Synthesis: An Asymmetric Entry to Highly Functionalized α‐Quaternary Proline Derivatives

Abstract: The highly enantioselective cascade reaction between N-protected a-cyanoglycine esters and a,beta-unsaturated aldehydes is disclosed. The reaction represents a one-step entry to polysubstituted 5-h ...

Direct Catalytic Asymmetric Synthesis of Pyrazolidine Derivatives

Abstract: A highly enantioselective, metal-free cascade reaction between di-1,2-N-protected hydrazine and α,β-unsaturated aldehydes is disclosed. The catalytic, asymmetric cascade transformation is a direct ...

Achiral Co-Catalyst Induced Switches in Catalytic Asymmetric Reactions on Racemic Mixtures (RRM): From Stereodivergent RRM to Stereoconvergent Deracemization by Combination of Hydrogen Bond Donating and Chiral Amine Catalysts

Abstract: A stereochemical divergent approach for the highly enantioselective synthesis of distinct bicyclic products with multiple stereocenters from a racemate using a single chiral catalyst is disclosed. ...

Direct Regiospecific and Highly Enantioselective Intermolecular α-Allylic Alkylation of Aldehydes by a Combination of Transition-Metal and Chiral Amine Catalysts.

Abstract: The present allylic alkylation of various linear aldehydes (II), catalyzed by an achiral palladium complex and a chiral amine as co-catalyst, gives the corresponding alcohols after in situ reduction with NaBH4.

One-Pot Three-Component Catalytic Enantioselective Synthesis of Homoallylboronates.

Abstract: The novel one-pot procedure is includes asymmetric hydroboration of α,β-unsaturated aldehydes followed by Wittig olefination to yield chiral homoallyl boronates.

Dynamic One‐Pot Three‐Component Catalytic Asymmetric Transformation by Combination of Hydrogen‐Bond‐Donating and Amine Catalysts.

Abstract: The reaction of aldehydes, protected α-cyanoglycinate esters, and enals is catalyzed by a combination of a chiral amine and an oxime derived from cyanoacetate ester as a hydrogen bond donating co-catalyst.

One‐Pot Three‐Component Highly Selective Synthesis of Homoallylboronates by Using Metal‐Free Catalysis.

Abstract: The first one-pot three-component reaction of α,β-unsaturated aldehydes with bis(pinacolatoborane) (II) and triphenylphosphoranylideneacetate (III) is presented, which proceeds readily in the presence of catalytic amounts of N,N′-dicyclohexylimidazolium salt.

One‐Step Catalytic Enantioselective α‐Quaternary 5‐Hydroxyproline Synthesis: An Asymmetric Entry to Highly Functionalized α‐Quaternary Proline Derivatives.

Abstract: The highly enantioselective cascade reaction between N-protected a-cyanoglycine esters and a,beta-unsaturated aldehydes is disclosed. The reaction represents a one-step entry to polysubstituted 5-h ...

Highly Enantioselective Co‐Catalytic Direct Aldol Reactions by Combination of Hydrogen‐Bond Donating and Acyclic Amino Acid Catalysts.

Abstract: Amino acid AMA in combination with the thiourea THU promotes the asymmetric aldol reaction of aldehydes with ketones.