The Clemmensen reduction is a chemical reaction which reduce aldehydes and ketones to alkanes.

In my book, it is written that under such conditions, double and triple bonds are not reduced, but my teacher told me of one exception:

α,β-unsaturated carbonyl compounds undergo reduction of both the olefinic and carbonyl group.

But according to my book, when this compound undergoes Clemmensen reduction, the product is pent-2-ene.

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Who is correct?


1 Answer 1


Both are not quite correct. A quick literature search doesn't turn up any hits for the Clemmensen reduction of this particular aldehyde, but March's Advanced Organic Chemistry, 7th ed. (p 1541) writes about the Clemmensen and Wolff-Kishner reductions:

Neither method is suitable for α,β-unsaturated ketones [...] Under Clemmensen conditions, both groups of these molecules may be reduced or if only one group is reduced, it is the C=C bond.

Large structural rearrangements are common under the vigorous conditions: see, for example, Helv. Chim. Acta 1976, 59, 962. "In all cases but one the formation of cyclopropyl acetates was observed."

It seems that there are some situations in which the ketone is selectively reduced, but this is not general: see Tetrahedron 1986, 42, 6615.


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