Remote electronic control in asymmetric cyclopropanation with chiral Ru-pybox catalysts

Modification of diphenylamine-linked bis(oxazoline) ligands: Tuning of electronic effect and rigidity of ligand skeleton

“…The mixture was refluxed for 2 h and methanol was removed under vacuum. The residue was extracted with CH 2 Cl 2 , washed with brine, and dried with anhydrous Na 2 SO 4 …”

“…As one part of ligand design, the modification of ligands at proper positions is important when a privileged ligand structure has been found, for the information on the structure-activity relationship obtained during this research process can direct the design of novel catalysts with enhanced efficiency. Besides the tuning of ligand steric effect which affects the selectivity of the catalytic process more directly, tuning of electronic effect has attracted more attention from the science community during recent years [1][2][3][4][5][6][7][8][9][10][11][12][13] . Not only the coordination ability of the ligands and the electronic density on the metal centers can be tuned, but also the inversion of the diastereoselectivity can be observed sometimes [12,13] .…”

Ruthenium‐Catalyzed Cyclopropanation

“…In 1980, a ruthenium-catalyzed cyclopropanation with Ru 2 (OAc) 4 Cl was reported in comparison with rhodium, palladium, or copper [19]. Ru 3 (CO) 12 showed the catalytic activity for styrene and EDA at 60 C [20].…”

“…Ru 3 (CO) 12 showed the catalytic activity for styrene and EDA at 60 C [20]. In addition, Ru 2 (OAc) 4 [21], Ru-polyethylene carboxylates [22], ruthenacarborane clusters [23], Ru 2 (CO) 4 (l-OAc) 2 / n [24], and RuCl 2 (Ph 3 P) 3 [25] catalyzed the cyclopropanation at 60~100 C to give moderate to higher yields and 60:40 to 70:30 ratios of the trans:cis isomers.…”

Arylid-Box: A new family of chiral bis-oxazoline ligands for metal mediated catalytic enantioselective synthesis

“…A current goal, one which has been taken up by Evans' group [11], is the investigation of bis-oxazoline ligands which can be electronically or stereochemically tuned to meet the requirements of the reaction and the substrates under study. Indeed, Nishiyama and co-workers [12] have looked at the influence of remote electronic control in asymmetric cyclopropanations with chiral Ru-Pybox catalysts and found that the enantioselectivity could be tuned with appropriate electron-withdrawing groups. Evans and co-workers [13] recently investigated the contribution of electronic effects on the reaction enantioselectivity of a series of Cu(II) catalysed Hetero-Diels-Alder reactions by incorporating both electron donating and withdrawing groups in the para position of both phenyl rings of their Box ligand.…”