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Relevant academic research and scientific papers

Chiral Phosphorus-Olefin Ligands for the RhI-Catalyzed Asymmetric Addition of Aryl Boronic Acids to Electron-Deficient Olefins

New chiral phosphorus-olefin hybrid ligands derived from the rigid "privileged" l-proline have been conveniently prepared and applied in the rhodium-catalyzed asymmetric arylation of electron-deficient olefins with arylboronic acids at room temperature; t

Chiral dihydrobenzofuran-based diphosphine (BICMAP): Optical resolution and application to rhodium(I)-catalyzed asymmetric 1,4-addition of aryl- and alkenylboronic acids to cyclic enones

Chiral dihydrobenzofuran-based diphosphine ligand (BICMAP) 1 was used as a ligand for the rhodium(I)-catalyzed asymmetric 1,4-addition of arylboronic acids to cyclic enones up to 99% ee. We also found that the BICMAP-rhodium system was an efficient catalyst for the 1,4-addition of alkenylboronic acids to 2-cyclohexenone in good enantioselectivities.

Polymer-incarcerated chiral Rh/Ag nanoparticles for asymmetric 1,4-addition reactions of arylboronic acids to enones: Remarkable effects of bimetallic structure on activity and metal leaching

Robust and highly active bimetallic Rh nanoparticle (NP) catalysts, PI/CB Rh/Ag, have been developed and applied to the asymmetric 1,4-addition of arylboronic acids to enones without leaching of the metals. We found that the structures of the bimetallic Rh/Ag catalysts and chiral ligands strongly affect their catalytic activity and the amount of metal leaching. PI/CB Rh/Ag could be recycled several times by simple operations while keeping high yields and excellent enantioselectivities. To show the versatility of the PI/CB Rh/Ag catalyst, a one-pot, oxidation-asymmetric 1,4-addition reaction of an allyl alcohol and an arylboronic acid was demonstrated by combining the PI/CB Rh/Ag catalyst with PI/CB Au as an aerobic oxidation catalyst.

Cu-catalyzed enantioselective 1,4-additions of aryl-Grignard reagents to cyclohexenone in the presence of TADDOL-derived phosphane-phosphite ligands

Asymmetric conjugate additions (1,4-additions) of aryl-Grignard reagents to cyclohex-2-enone, currently a more or less unsolved challenge, were investigated. For this purpose, a small library of phenol-derived chiral phosphane-phosphite ligands containing TADDOL- or BINOL-based phosphite moieties was evaluated. These ligands are easily prepared by a short modular scheme previously developed in this laboratory. Two particularly powerful ligands (4a and 4b, both TADDOL-derived and each possessing a bulky tert-butyl substituent ortho to the phosphite group) were identified. Conditions were optimized with use of the addition of (4-methoxyphenyl)magnesium bromide to cyclohexenone as a standard reaction system. Under optimized conditions [CuBr·SMe 2 (4 mol-%), ligand 4a (6 mol-%), 2-methyl-THF, -78 °C, slow addition of Grignard reagent] the 1,4-product was obtained with high enantioselectivity (up to 95 % ee) and good regioselectivity (r.r. = 90:10). The scope of the method was probed with different aryl-Grignard reagents. It was found that reagents with electron-donating substituents in meta- or para-positions performed particularly well, whereas the presence of F or CF 3 substituents led to decreased ee values. Only ortho-substituted aryl-Grignard reagents did not give rise to useful results. A series of phosphane-phosphite ligands were also tested in the Rh-catalyzed 1,4-addition of phenylboronic acid to cyclohexenone, but enantioselectivities did not exceed 70 % ee in this case. The difficult task of employing aryl-Grignard reagents in Cu-catalyzed enantioselective 1,4 addition reactions was achieved with the assistance of readily accessible chiral modular P,P ligands. High enantioselectivities were obtained in a number of synthetically relevant cases. Copyright

Chiral sulfoxide-olefin ligands: Completely switchable stereoselectivity in rhodium-catalyzed asymmetric conjugate additions

Have it both ways: A novel class of chiral sulfoxide-olefin ligands was synthesized from a single chiral source. These ligands were evaluated in rhodium-catalyzed 1,4-additions of arylboronic acids to electron-deficient olefins, and remarkable olefin-directed reversal of stereoselectivity (up to >99 ee, R isomer; 98 ee, S isomer) was observed when the reversal ligand pair L1 (branched olefin) and L2 (linear olefin) were utilized (see scheme). Copyright

Chiral N-tert-butanesulfinyl α,β-unsaturated ketimine: A simple and highly effective olefin/sulfinimide hybrid ligand for asymmetric 1,4-additions

One novel type of chiral olefin/sulfinimide hybrid ligands has been developed through a simple one-step condensation of α,β-unsaturated ketones with tert-butanesulfinamide and utilized successfully for rhodium-catalyzed asymmetric conjugated additions to furnish the desired adducts in high yields with excellent ee's.