Application In Asymmetric Henry Reaction Research Articles

Chiral Ni-Schiff Base Complexes inside Zeolite-Y and Their Application in Asymmetric Henry Reaction: Effect of Initial Activation with Microwave Irradiation

Chiral Ni(II)-Schiff base complexes synthesized inside the cavity of zeolite-Y were used as heterogeneous chiral catalyst for asymmetric Henry reaction. Synthesized catalysts were characterized using various spectrochemical and physicochemical techniques. Solid state NMR analysis has been used to confirm the internal location of the metal complexes. To the best of our knowledge MAS NMR has not been used to characterize chiral diamagnetic Ni2+-Schiff base complex inside zeolite-Y. The catalytic activities of the materials were dependent on temperature, solvent, and amount of catalyst. High catalytic transformation of aldehydes with nitromethane to nitro-aldol product (92% yield and 83% ee, S-isomer) was achieved at −10 °C. Initial activation of the reaction with microwave irradiation for 15 min leads to a substantial decrease in the reaction time in comparison to normal stirring. Heterogeneous catalysts were found to be advantageous over the homogeneous counterparts in terms of recyclability of the catalys...

ChemInform Abstract: Fluorous Chiral Bis(oxazolines): Synthesis and Application in Asymmetric Henry Reaction.

AbstractThe newly synthesized ligand can be easily recovered and reused at least three times without significant loss of activity.

Synthesis and computation of diastereomeric phenanthroline–quinine ligands and their application in asymmetric Henry reaction

A class of chiral ligands has been developed by combining phenanthroline with quinine in a one-step method that does not require resolution. The synthesized three ligands were then coordinated with Cu(II) and the performance of the resultant chiral catalysts in the asymmetric Henry reaction was evaluated. Moderate to good yields (up to 86%) with high enantioselectivities (up to 99% ee) were observed in the reactions catalyzed by one of the three catalysts. Theoretical calculations were performed to analyze the catalytic activities of the different Cu(II)-ligand catalysts. Three different ligands were investigated and one ligand was found to adopt an unexpected five-coordinated mode; the second coordinated with two nitrogen atoms of phenanthroline to give a complex, which activated both substrates of Henry reaction; the third was unable to form a complex with Cu(II).

Fluorous chiral bis(oxazolines): Synthesis and application in asymmetric Henry reaction

A fluorous bis(oxazolines) was synthesized by a facile two-step process using malononitrile as the starting material. The compound was tested as a chiral ligand in copper-catalyzed Henry reactions of nitromethane with different aldehydes to afford the corresponding β-nitroalcohols in 61–75% yield with enantioselectivities up to 99%. Furthermore, the fluorous ligand can be easily recovered and reused without significant loss in its activity.

Synthesis of novel thiophene‐based chiral ligands and their application in asymmetric Henry reaction

Novel chiral thiolated amino alcohols were synthesized from norephedrine and thiophene carbaldehydes (methyl‐ or ethyl‐substituted) and applied to the catalytic asymmetric Henry reaction of various aldehydes with nitromethane to provide β‐hydroxy nitroalkanols in high conversion (92%). The reaction was optimized in terms of the metal, solvent, temperature and amount of chiral ligand. The corresponding catalyst with Cu(OTf)2 and 2‐propanol as the solvent provided the best enantioselectivities (up to 96% ee) of the corresponding nitroalcohols for aliphatic aldehydes. Copyright © 2013 John Wiley & Sons, Ltd.

Noncovalent Immobilization of Ionic-tagged Box-Cu(OAc)2 Complex and Its Application in Asymmetric Henry Reaction

Immobilized Cu(OAc)(2)-bis(oxazolines) via hydrogen bonding by SBA-15 was applied to asymmetric Henry reaction, and good enantioselectivities were obtained (up to 83% ee) between 2-methoxybenzaldehyde and CH(3)NO(2) in isopropyl alcohol (iPrOH). The catalyst could be reused seven times without any obvious loss in enantioselectivity. For the first time, this facile and clean immobilization method is applied to the use of bis(oxazolines) complexes.

Synthesis of new planar chiral [2.2]paracyclophane Schiff base ligands and their application in the asymmetric Henry reaction

A series of new planar and central chiral ligands based on [2.2]paracyclophane backbones were designed and prepared from enantiomerically pure 4-amino-13-bromo[2.2]paracyclophane and commercially available chiral amino alcohols. Their application in a copper-catalyzed asymmetric Henry reaction resulted in secondary alcohols with high yield and excellent selectivity for active aldehydes (up to 94% ee). This is a successful example of employing planar chiral [2.2]paracyclophane ligands in copper-catalyzed reaction.