Iron (low valent)
Fe(0) is cost-effective, environmentally friendly alternative to Cr(II) for the olefination of carbonyls by activated polyhalides. Fe(0) proved compatible with a wide range of functionality, such as unprotected phenol, aryl nitro, carboxylic acid, and alkyl nitrile.
J. R. Falck, R. Bejot, D. K. Barma, A. Bandyopadhyay, S. Joseph, C. Mioskowski, J. Org. Chem., 2006, 71, 8178-8182.
An operationally simple and very efficient Reformatsky reaction of aldehydes has been carried out in THF in the presence of low valent iron or copper which were prepared in situ employing a bimetal redox strategy through reduction of Fe(III) or Cu(II) salts with magnesium.
A. Chattopadhyay, A. Kr. Dubey, J. Org. Chem., 2007, 72, 9357-9359.
An iron complex containing electronically coupled acidic and hydridic hydrogens catalyzes the hydrogenation of ketones under mild conditions and shows high chemoselectivity for aldehydes, ketones, and imines. Isolated carbon double and triple bonds, aryl halides, nitrates, epoxides, and ester functions are unaffected by the hydrogenation conditions.
C. P. Casey, H. Guan, J. Am. Chem. Soc., 2007, 129, 5816-5817.
A facile and practical method for the synthesis of N-acetyl α-arylenamides from the corresponding ketoximes with ferrous acetate as the reducing reagent offers mild reaction conditions, simple purification procedures, and high yields for a variety of N-acetyl enamides.
W. Tang, A. Capacci, M. Sarvestani, X. Wei, N. K. Yee, C. H. Senanayake, J. Org. Chem., 2009, 74, 9528-9530.
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.
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.
Reduction of o-nitroarylcarbaldehydes o-aminoarylcarbaldehydes with iron in the presence of a catalytic amount of aqueous hydrochloric acid followed by in situ condensation of the resulting amines with ketones or aldehydes (Friedlaender quinoline synthesis) gives mono- or disubstituted quinolines, respectively, in very good yields.
A.-H. Li, D. J. Beard, H. Coate, A. Honda, M. Kadablbajoo, A. Kleinberg, R. Laufer, K. M. Mulvihill, A. Nigro, P. Rastogi, M. W. Siu, A. G. Steinig, T. Wang, D. Werner, A. P. Crew, M. J. Mulvihill, Synthesis, 2010, 1629-1632.
A tandem condensation of a cyanoimidate with an amine followed by reductive cyclization in an iron-HCl system enables an efficient route to N4-substituted 2,4-diaminoquinazolines. An additional N-alkylation can produce two fused heterocycles in a one-pot procedure.
P. Yin, N. Liu, Y.-X. Deng, Y. Chen, Y. Deng, L. He, J. Org. Chem., 2012, 77, 2649-2658.