Is it possible to reduce an acyl group to an alkane, but still keep a nitro group intact without its reduction to an amino group? A Clemmensen reduction would reduce the nitro group, and it seems like other reducing agents will also reduce the nitro group to an amino group. Would some other mechanism be better suited for this reaction?

For instance, how can I selectively reduce 1-(3-nitrophenyl)propan-1-one to 1-nitro-3-propylbenzene?

Reaction scheme


2 Answers 2


You will most likely be successful if you convert the ketone to the corresponding tosylhydrazone and reduce that with $\ce{NaCNBH3}$ (DOI).

A previous study (Bull. Chem. Soc. Jpn., 1974, 47, 2323-2324) has shown that the tosylhydrazone of cyclohexanone can be reduced to cyclohexane with $\ce{NaBH4}$ in polar aprotic solvents.

$\ce{NaCNBH3}$ is an even milder hydride transfer agent, that has been widely used in the reduction of imines and iminium salts. A review by C.F.Lane, Sodium Cyanoborohydride - A Highly Selective Reducing Agent for Organic Functional Groups in Synthesis, 1975, 3, 135-146 gives some background information on the versatility of this reagent.

The nitro group is definitely safe with $\ce{NaCNBH3}$. However, considering the high toxicity and the price for this reagent, you might want to run a small scale reduction of your tosylhydrazone with the much cheaper $\ce{NaBH4}$ first.


A discussion about alternative reduction methods was here Clemmensen reduction vs. Wolff-Kishner reduction. I've not seen nitro groups reduced by the acid-triethylsilane or tetramethyldisiloxane treatment. One used on plant that I've seen (and used) is TFA - triethylsilane. The carbonyl is protonated and the first hydride delivery gives the alcohol. A second protonation and hydride addition gives the methylene. As a side note, any aromatics that are not electron deficient e.g. the solvent toluene, can undergo an electrophilic addition during the second reduction step when water is lost.


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