Categories: N-H Bond Formation >
Reduction of azo compounds
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Recent Literature
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.
N,N-Diisopropylethylamine mediates a cathodic reduction approach for the
hydrogenation of azobenzenes in dichloromethane as hydrogen source. The reaction
proceeded smoothly in a simple undivided cell under constant-current
electrolysis. A series of azobenzenes were successfully reduced to the
corresponding hydrazobenzenes in good yields at room temperature.
H. Zhou, R. Fan, J. Yang, X. Sun, X. Liu, X.-C. Wang, J. Org. Chem., 2022, 87,
14536-14543.
A visible-light-promoted transfer hydrogenation of azobenzenes proceeds
smoothly in methanol at ambient temperature in the presence of B2pin2
through a radical pathway. The reaction reduces a broad range of azobenzenes to
the corresponding hydrazobenzenes in very good yields.
M. Song, H. Zhou, G. Wang, B. Ma, Y. Jiang, J. Yang, C. Huo, X.-C. Wang, J. Org. Chem., 2021, 86,
4804-4811.
A bidentate Ru(II)-NC complex catalyzes a transfer hydrogenation of azoarenes
to hydrazoarenes using ethanol as a hydrogen source in the presence of a weak
base. Control experiments and density functional theory calculations suggest a
Meerwein-Ponndorf-Verley mechanism with ethyl acetate as the byproduct.
D. Gong, D. Kong, N. Xu, Y. Hua, B. Liu, Z. Xu, Org. Lett.,
2022, 24, 7339-7343.
Various azobenzenes have been reduced to the corresponding hydrazines by using
an aqueous solution of sodium dithionite. The yield is generally excellent, but
two compounds, viz. 4,4-dimethoxyazobenzene and
2,2,4,4,6,6-hexamethylazobenzene, gave no hydrazine at all.
L. K. Sydnes, S. Elmi, P. Heggen, B. Holmelid, D. Malthe-Sørensen, Synlett, 2007,
1695-1696.
