Categories: N-H Bond Formation >
Reduction of nitro compounds
A well-defined iron-based catalyst system enables the reduction of nitroarenes to anilines using formic acid as reducing agent. A broad range of substrates including other reducible functional groups were converted to the corresponding anilines in good to excellent yields at mild conditions. Notably, the process constitutes a rare example of base-free transfer hydrogenations.
G. Wienhöfer, I. Sorribes, A. Boddien, F. Westerhaus, K. Junge, H. Junge, R. Llusar, M. Beller, J. Am. Chem. Soc., 2011, 133, 12875-12879.
Palladium-catalyzed reduction of aromatic nitro groups to amines can be accomplished in high yield, with wide functional group tolerance and short reaction times at r.t. using aqueous potassium fluoride and polymethylhydrosiloxane (PMHS) for aromatic nitro groups. Aliphatic nitro compounds are reduced to the corresponding hydroxylamines using triethylsilane instead of PMHS/KF.
R. J. Rahaim, R. E. Maleczka (Jr.), Org. Lett., 2005, 7, 5087-5090.
Vasicine, an abundantly available quinazoline alkaloid from the leaves of Adhatoda vasica, enables an efficient metal- and base-free reduction of nitroarenes to the corresponding anilines in water. The chemoselective method tolerates a wide range of reducible functional groups, such as ketones, nitriles, esters, halogens, and heterocyclic rings. Dinitroarenes are reduced selectively to the corresponding nitroanilines.
S. Sharma, M. Kumar, V. Kumar, N. Kumar, J. Org. Chem., 2014, 79, 9433-9439.
A robust and green protocol for the reduction of functionalized nitroarenes to the corresponding primary amines relies on inexpensive zinc dust in water containing nanomicelles derived from the commercially available designer surfactant TPGS-750-M. This mild process takes place at room temperature and tolerates a wide range of functionalities including common protecting groups.
S. M. Kelly, B. H. Lipshutz, Org. Lett., 2014, 16, 98-101.
An efficient Fe/CaCl2 system enables the reduction of nitroarenes and reductive cleavage of azo compounds by catalytic transfer hydrogenation in the presence of sensitive functional groups including halides, carbonyl, aldehyde, acetyl, nitrile, and ester substituents with excellent yields. The simple experimental procedure and easy purification make the protocol advantageous.
S. Chandrappa, T. Vinaya, T. Ramakrishnappa, K. S. Rangappa, Synlett, 2010, 3019-3022.
A mild and efficient electron-transfer method for the chemoselective reduction of aromatic nitro groups using samarium(0) metal in the presence of a catalytic amount of 1,1'-dioctyl-4,4'-bipyridinium dibromide gives aromatic amines in good yield with selectivity over a number of other functional and protecting groups.
C. Yu, B. Liu, L. Hu, J. Org. Chem., 2001, 66, 919-924.
(Ph3P)3RuCl2 is an inexpensive catalyst, that enables a chemoselective reduction of alkyne, ketones, or nitro groups in the presence of Zn/water as a stoichiometric reductant. Depending on the nature of the additive and the temperature, chemoselective reduction of a nitro group in the presence of a ketone or an alkyne was possible.
T. Schabel, C. Belger, B. Plietker, Org. Lett., 2013, 15, 2858-2861.
A generally applicable method for the introduction of gaseous hydrogen into a sealed reaction system under microwave irradiation allows the hydrogenation of various substrates in short reaction times with moderate temperatures between 80 °C and 100 °C with 50 psi of hydrogen.
G. S. Vanier, Synlett, 2007, 131-135.
Poly(ethylene glycol) (PEG) (400) has been found to be a superior solvent over ionic liquids by severalfold in promoting the hydrogenation of various functional groups using Adams' catalyst. Both the catalyst and PEG were recycled efficiently over 10 runs without loss of activity, and without substrate cross contamination.
S. Chandrasekhar, S. Y. Prakash, C. L. Rao, J. Org. Chem., 2006, 71, 2196-2199.
Several bromo, chloro, iodo and multihalogenated nitroarenes have been selectively reduced with hydrazine hydrate in the presence of Pd/C to give the corresponding halogenated anilines in good yield. Using microwave irradiation at elevated temperature and pressure, dehalogenated products can be isolated.
F. Li, B. Frett, H.-y Li, Synlett, 2014, 25, 1403-1408.
A microwave-assisted, palladium-catalyzed catalytic transfer hydrogenation of different homo- or heteronuclear organic compounds using formate salts as a hydrogen source was performed in ([bmim][PF6]. Essentially pure products could be isolated in moderate to excellent yields by simple liquid-liquid extraction.
H. Berthold, T. Schotten, H. Hönig, Synthesis, 2002, 1607-1610.
N-Alkylaminobenzenes were prepared in a simple and efficient one-pot synthesis by reduction of nitrobenzenes followed by reductive amination with decaborane (B10H14) in the presence of 10% Pd/C.
J. W. Bae, Y. J. Cho, S. H. Lee, C.-O. M. Yoon, C. M. Yoon, Chem. Commun., 2000, 1857-1858.
A synthesis of N-arylsulfonamides from readily available nitroarenes and sodium arylsulfinates was realized in the presence of FeCl2 as catalyst and NaHSO3 as reductant under mild conditions. A broad range of functional groups were tolerated. Mechanistic studies indicated that the N-S bond might be generated through direct coupling of nitroarene with sodium arylsulfinate prior to the reduction.
W. Zhang, J. Xie, B. Rao, M. Luo, J. Org. Chem., 2015, 80, 3504-3511.
In the presence of iodide ions, an efficient and selective rhodium-catalyzed transfer hydrogenation of nitroarenes with formic acid as the hydrogen source takes place to give amines or formanilides.
Y. Wei, J. Wu, D. Xue, C. Wang, Z. Liu, Z. Zhang, G. Chen, J. Xiao, Synlett, 2014, 25, 1295-1298.
The combination of zinc powder as reductant and sodium chlorate as oxidant was used to provide an environmentally friendly, effective, and convenient method for the synthesis of aromatic amides in good yields from nitroarenes and aldehydes in a green solvent under atmospheric conditions. Reductants and oxidants with opposing properties can be used together without any adverse effects. In addition, a cooperation seems to improve the yield.
G. Sheng, X. Wu, X. Cai, W. Zhang, Synthesis, 2015, 47, 949-954.
An efficient one-pot procedure for the zinc-mediated reduction of nitroarenes in the presence of chloroformates leads to the corresponding N,O-bisprotected hydroxylamines in good yield under ambient conditions in THF-water mixtures. Solvolysis of the bisprotected hydroxylamines with sodium methoxide at room temperature provides access to synthetically versatile N-aryl-N-hydroxy carbamates in excellent yields.
A. Porzelle, M. D. Woodrow, N. C. O. Tomkinson, Synlett, 2009, 798-802.
An intermolecular reductive Schiff base formation from nitroarenes and benzaldehydes to yield diarylimines is carried out in the presence of iron powder and dilute acid. This process tolerates various functional groups and often proceeds quantitatively with no need for purification.
A. L. Korich, T. S. Hughes, Synlett, 2007, 2602-2604.