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Full-Text Articles in Physical Sciences and Mathematics
Enantioselective Total Syntheses Of (−)-Taiwaniaquinone H And (−)-Taiwaniaquinol B By Iridium-Catalyzed Borylation And Palladium-Catalyzed Asymmetric Α-Arylation, Xuebin Liao, Levi M. Stanley, John F. Hartwig
Enantioselective Total Syntheses Of (−)-Taiwaniaquinone H And (−)-Taiwaniaquinol B By Iridium-Catalyzed Borylation And Palladium-Catalyzed Asymmetric Α-Arylation, Xuebin Liao, Levi M. Stanley, John F. Hartwig
Levi M. Stanley
We report a concise, enantioselective total synthesis of (−)-taiwaniaquinone H and the first enantioselective total synthesis of (−)-taiwaniaquinol B by a route that includes asymmetric palladium-catalyzed α-arylation of a ketone with an aryl bromide that was generated by sterically controlled halogenation via iridium-catalyzed C−H borylation. This asymmetric α-arylation creates the benzylic quaternary stereogenic center present in the taiwaniaquinoids. The synthesis was completed efficiently by developing a Lewis acid-promoted cascade to construct the [6,5,6] tricyclic core of an intermediate common to the synthesis of a number of taiwaniaquinoids. Through the preparation of these compounds, we demonstrate the utility of constructing benzylic …
Mechanistically Driven Development Of Iridium Catalysts For Asymmetric Allylic Substitution, John F. Hartwig, Levi M. Stanley
Mechanistically Driven Development Of Iridium Catalysts For Asymmetric Allylic Substitution, John F. Hartwig, Levi M. Stanley
Levi M. Stanley
Enantioselective allylic substitution reactions comprise some of the most versatile methods for preparing enantiomerically enriched materials. These reactions form products that contain multiple functionalities by creating carbon−nitrogen, carbon−oxygen, carbon−carbon, and carbon−sulfur bonds. For many years, the development of catalysts for allylic substitution focused on palladium complexes. However, studies of complexes of other metals have revealed selectivities that often complement those of palladium systems. Most striking is the observation that reactions with unsymmetrical allylic electrophiles that typically occur with palladium catalysts at the less hindered site of an allylic electrophile occur at the more hindered site with catalysts based on other …
Iridium-Catalyzed Kinetic Asymmetric Transformations Of Racemic Allylic Benzoates, Levi M. Stanley, Chen Bai, Mitsuhiro Ueda, John F. Hartwig
Iridium-Catalyzed Kinetic Asymmetric Transformations Of Racemic Allylic Benzoates, Levi M. Stanley, Chen Bai, Mitsuhiro Ueda, John F. Hartwig
Levi M. Stanley
Versatile methods for iridium-catalyzed, kinetic asymmetric substitution of racemic, branched allylic esters are reported. These reactions occur with a variety of aliphatic, aryl, and heteroaryl allylic benzoates to form the corresponding allylic substitution products in high yields (74−96%) with good to excellent enantioselectivity (84−98% ee) with a scope that encompasses a range of anionic carbon and heteroatom nucleophiles. These kinetic asymmetric processes occur with distinct stereochemical courses for racemic aliphatic and aromatic allylic benzoates, and the high reactivity of branched allylic benzoates enables enantioselective allylic substitutions that are slow or poorly selective with linear allylic electrophiles.
Diels−Alder Cycloaddition Strategy For Kinetic Resolution Of Chiral Pyrazolidinones, Mukund P. Sibi, Keisuke Kawashima, Levi M. Stanley
Diels−Alder Cycloaddition Strategy For Kinetic Resolution Of Chiral Pyrazolidinones, Mukund P. Sibi, Keisuke Kawashima, Levi M. Stanley
Levi M. Stanley
A rare example of the application of a catalytic, enantioselective Diels−Alder cycloaddition to affect a kinetic resolution has been developed. Chiral pyrazolidinones are resolved with high selectivity through a process that utilizes a relay of stereochemical information from a permanent chiral center to a fluxional chiral center to enhance the inherent selectivity of the chiral Lewis acid catalyst.
Enantioselective, Iridium-Catalyzed Monoallylation Of Ammonia, Mark J. Pouy, Levi M. Stanley, John F. Hartwig
Enantioselective, Iridium-Catalyzed Monoallylation Of Ammonia, Mark J. Pouy, Levi M. Stanley, John F. Hartwig
Levi M. Stanley
Highly enantioselective, iridium-catalyzed monoallylations of ammonia are reported. These reactions occur with electron-neutral, -rich, and -poor cinnamyl carbonates, alkyl and trityloxy-substituted allylic carbonates, and dienyl carbonates in moderate to good yields and excellent enantioselectivities. This process is enabled by the use of an iridium catalyst that does not require a Lewis acid for activation and that is stable toward a large excess of ammonia. This selective formation of primary allylic amines allows for one-pot syntheses of heterodiallylamines and allylic amides that are not otherwise accessible via iridium-catalyzed allylic amination without the use of blocking groups and protective group manipulations.
Regio- And Enantioselective N-Allylations Of Imidazole, Benzimidazole, And Purine Heterocycles Catalyzed By Single-Component Metallacyclic Iridium Complexes, Levi M. Stanley, John F. Hartwig
Regio- And Enantioselective N-Allylations Of Imidazole, Benzimidazole, And Purine Heterocycles Catalyzed By Single-Component Metallacyclic Iridium Complexes, Levi M. Stanley, John F. Hartwig
Levi M. Stanley
Highly regio- and enantioselective iridium-catalyzed N-allylations of benzimidazoles, imidazoles, and purines have been developed. N-Allylated benzimidazoles and imidazoles were isolated in high yields (up to 97%) with high branched-to-linear selectivity (up to 99:1) and enantioselectivity (up to 98% ee) from the reactions of benzimidazole and imidazole nucleophiles with unsymmetrical allylic carbonates in the presence of single component, ethylene-bound, metallacyclic iridium catalysts. N-Allylated purines were also obtained in high yields (up to 91%) with high N9/N7 selectivity (up to 96:4), high branched-to-linear selectivity (98:2), and high enantioselectivity (up to 98% ee) under similar conditions. The reactions encompass a range of benzimidazole, …
Enantioselective Copper-Catalyzed 1,3-Dipolar Cycloadditions, Levi M. Stanley, Mukund P. Sibi
Enantioselective Copper-Catalyzed 1,3-Dipolar Cycloadditions, Levi M. Stanley, Mukund P. Sibi
Levi M. Stanley
The addition of a 1,3-dipole to an alkene or alkyne is a prominent transformation in organic synthesis.(1) Over the past two decades the intense study of enantioselective 1,3-dipolar cycloaddition methodologies has provided organic chemists with the tools necessary to synthesize a variety of chiral heterocycles in highly enantioenriched forms.(2) The majority of advances in this area are a direct result of studies focusing on chiral Lewis acid-catalyzed or chiral metal-mediated 1,3-dipolar cycloaddition methodologies. It is important to note that even though the many dipoles possess very strong donor atoms it is still possible to carry out enantioselective Lewis acid-catalyzed dipolar …
Copper(Ii)-Catalyzed Exo And Enantioselective Cycloadditions Of Azomethine Imines, Mukund P. Sibi, Digamber Rane, Levi M. Stanley, Takahiro Soeta
Copper(Ii)-Catalyzed Exo And Enantioselective Cycloadditions Of Azomethine Imines, Mukund P. Sibi, Digamber Rane, Levi M. Stanley, Takahiro Soeta
Levi M. Stanley
A strategy for exo and enantioselective 1,3-dipolar cycloaddition of azomethine imines to 2-acryloyl-3-pyrazolidinone is described. The corresponding cycloadducts are isolated with high diastereoselectivities (up to >96:4 exo/endo) and enantioselectivities (up to 98% ee).
Enantioselective 1,3-Dipolar Cycloadditions Of Diazoacetates With Electron-Deficient Olefins, Mukund P. Sibi, Levi M. Stanley, Takahiro Soeta
Enantioselective 1,3-Dipolar Cycloadditions Of Diazoacetates With Electron-Deficient Olefins, Mukund P. Sibi, Levi M. Stanley, Takahiro Soeta
Levi M. Stanley
A general strategy for highly enantioselective 1,3-dipolar cycloaddition of diazoesters to β-substituted, α-substituted, and α,β-disubstituted α,β-unsaturated pyrazolidinone imides is described. Cycloadditions utilizing less reactive α,β-disubstituted dipolarophiles require elevated reaction temperatures, but still provide the corresponding pyrazolines with excellent enantioselectivities. Finally, an efficient synthesis of (−)-manzacidin A employing this cycloaddition methodology as a key step is illustrated.
The Role Of Achiral Pyrazolidinone Templates In Enantioselective Diels−Alder Reactions: Scope, Limitations, And Conformational Insights, Mukund P. Sibi, Levi M. Stanley, Xiaoping Nie, Lakshmanan Venkatraman, Mei Liu, Craig P. Jasperse
The Role Of Achiral Pyrazolidinone Templates In Enantioselective Diels−Alder Reactions: Scope, Limitations, And Conformational Insights, Mukund P. Sibi, Levi M. Stanley, Xiaoping Nie, Lakshmanan Venkatraman, Mei Liu, Craig P. Jasperse
Levi M. Stanley
We have evaluated the role of achiral pyrazolidinone templates in conjunction with chiral Lewis acids in room temperature, enantioselective Diels−Alder cycloadditions. The role of the fluxional N(1) substituent was examined, with the bulky 1-naphthylmethyl group providing enantioselectivities up to 99% ee, while templates with smaller fluxional groups gave lower selectivities. High selectivities were also observed in reactions of 7d with chiral Lewis acids derived from relatively small chiral ligands, suggesting the pyrazolidinone templates are capable of relaying stereochemical information from the ligand to the reaction center. Lewis acids capable of adapting square planar geometries, such as Cu(OTf)2, Cu(ClO4)2, and Pd(ClO4)2, …
An Entry To A Chiral Dihydropyrazole Scaffold: Enantioselective [3 + 2] Cycloaddition Of Nitrile Imines, Mukund P. Sibi, Levi M. Stanley, Craig P. Jasperse
An Entry To A Chiral Dihydropyrazole Scaffold: Enantioselective [3 + 2] Cycloaddition Of Nitrile Imines, Mukund P. Sibi, Levi M. Stanley, Craig P. Jasperse
Levi M. Stanley
We have developed a versatile strategy to access dihydropyrazoles in highly enantioenriched form. Dipolar cycloaddition of electron-deficient acceptors and in situ-generated nitrile imines proceeds with high regio- and enantioselectivity using 10 mol % chiral Lewis acid catalyst. A variety of dihydropyrazoles that incorporate functionality for further manipulation have been prepared.