Wolff–Kishner reduction | EPFL Graph Search

The Wolff–Kishner reduction is a reaction used in organic chemistry to convert carbonyl functionalities into methylene groups. In the context of complex molecule synthesis, it is most frequently employed to remove a carbonyl group after it has served its synthetic purpose of activating an intermediate in a preceding step. As such, there is no obvious retron for this reaction. The reaction was reported by Nikolai Kischner in 1911 and Ludwig Wolff in 1912. In general, the reaction mechanism first involves the in situ generation of a hydrazone by condensation of hydrazine with the ketone or aldehyde substrate. Sometimes it is however advantageous to use a pre-formed hydrazone as substrate (see modifications). The rate determining step of the reaction is de-protonation of the hydrazone by an alkoxide base to form a diimide anion by a concerted, solvent mediated protonation/de-protonation step. Collapse of this alkyldiimide with loss of N2 leads to formation of an alkylanion which can be

Cooperative Effects between Chiral Cp-x-Iridium(III) Catalysts and Chiral Carboxylic Acids in Enantioselective C-H Amidations of Phosphine Oxides

Nicolai Cramer, Michael Christian Dieckmann, Yun-Suk Jang

An enantioselective C-H amidation of phosphine oxides by using an iridium(III) catalyst bearing an atropchiral cyclopentadienyl (Cp-x) ligand is reported. A very strong cooperative effect between the chiral Cp-x ligand and a phthaloyl tert-leucine enabled the transformation. Matched-mismatched cases of the different acid enantiomers are shown. The amidated P-chiral arylphosphine oxides are formed in yields of up to 95% and with excellent enantioselectivities of up to 99:1 er. Enantiospecific reduction provides access to valuable P-chiral phosphorus(III) compounds.

Wiley-Blackwell2017

Selective three-phase hydrogenation of aromatic nitro-compounds over beta-molybdenum nitride

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey

A tetragonal molybdenum nitride (beta-Mo2N) has been prepared by temperature programmed treatment of MoO3 in flowing N-2 + H-2 and for the first time shown to catalyze the liquid phase selective hydrogenation (T = 423 K; P-H2 = 11 bar) of a series of para-substituted (-H, -OH, -O-CH3, -CH3, -Cl, -I and -NO2) nitrobenzenes to give the corresponding aromatic amine. Reaction over Pd/Al2O3, as a benchmark catalyst (Pd particle size ca. 18 nm), resulted in a composite hydrodechlorination/hydrogenation of p-chloronitrobenzene (as a representative nitroarene) to generate nitrobenzene and aniline. beta-Mo2N has been characterized in terms of temperature-programmed reduction (TPR), H-2 chemisorption/temperature programmed desorption (TPD), BET surface area/pore volume, elemental analysis, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopy. Elemental analysis, XRD, SEM and TEM have confirmed the formation of tetragonal beta-Mo2N, characterized by an agglomeration of flake-like crystallites. Post-synthesis, the nitride was passivated by contact with 1% (v/v) O-2/He at ambient temperature and XPS analysis has demonstrated the formation of a superficial passivating oxide overlayer without bulk oxidation. Pre-reaction, activation by TPR to 673 K was necessary to remove the passivating film. Hydrogen TPD has revealed significant hydrogen uptake (0.7 mu mol m(-2)) associated with beta-Mo2N. Nitro group reduction kinetics have been subjected to a Hammett treatment where the reaction constant (p = 0 4) is diagnostic of an increase in rate due to the presence of electron-withdrawing substituents on the aromatic ring, consistent with a nucleophilic mechanism. The results presented in this study establish the viability of beta-Mo2N to promote selective nitroarene hydrogenation. (C) 2011 Elsevier B.V. All rights reserved.

2011

Selective three-phase hydrogenation of aromatic nitro-compounds over β-molybdenum nitride

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey

A tetragonal molybdenum nitride (β-Mo2N) has been prepared by temperature programmed treatment of MoO3 in flowing N2 + H2 and for the first time shown to catalyze the liquid phase selective hydrogenation (T = 423 K; PH2=11bar) of a series of para-substituted (-H, -OH, -O-CH3, -CH3, -Cl, -I and -NO2) nitrobenzenes to give the corresponding aromatic amine. Reaction over Pd/Al2O3, as a benchmark catalyst (Pd particle size ca. 18 nm), resulted in a composite hydrodechlorination/ hydrogenation of p-chloronitrobenzene (as a representative nitroarene) to generate nitrobenzene and aniline. β-Mo2N has been characterized in terms of temperature-programmed reduction (TPR), H2 chemisorption/temperature programmed desorption (TPD), BET surface area/pore volume, elemental analysis, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopy. Elemental analysis, XRD, SEM and TEM have confirmed the formation of tetragonal β-Mo2N, characterized by an agglomeration of flake-like crystallites. Post-synthesis, the nitride was passivated by contact with 1% (v/v) O2/He at ambient temperature and XPS analysis has demonstrated the formation of a superficial passivating oxide overlayer without bulk oxidation. Pre-reaction, activation by TPR to 673 K was necessary to remove the passivating film. Hydrogen TPD has revealed significant hydrogen uptake (0.7 μmol m-2) associated with β-Mo2N. Nitro group reduction kinetics have been subjected to a Hammett treatment where the reaction constant (p = 0 4) is diagnostic of an increase in rate due to the presence of electron-withdrawing substituents on the aromatic ring, consistent with a nucleophilic mechanism. The results presented in this study establish the viability of β-Mo2N to promote selective nitroarene hydrogenation. © 2011 Elsevier B.V. All rights reserved.

Elsevier2011

Selective three-phase hydrogenation of aromatic nitro-compounds over β-molybdenum nitride

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey

Elsevier2011

Selective three-phase hydrogenation of aromatic nitro-compounds over beta-molybdenum nitride

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey

2011