Dibenzylideneacetone is a well known dienone|thumb|right|240px
A dienone is a class of organic compounds with the general formula, where R is any substituent, but often H. They are formally "derived from 1,4-diene compounds by conversion of a –CH2– group into –C(=O)– group", resulting in "a conjugated structure". They are a kind of enone. The class includes some heterocyclic compounds.
There is no evidence that phenols tautomerizes to a dienone, but such tautomerism is well recognized for resorcinols and some hydroxypyridines.
Being multifunctional, dienones engage in many reactions. They are often good dienophiles. They function as ligands, forming metal-alkene complexes such as tris(dibenzylideneacetone)dipalladium(0).
Extensive work has been reported on cyclic dienones. The parent of the seven-membered ring series is tropone. It is a not only a dienone but a trieneone.
Cyclohexadienones are a significant class of dienones, the premier members being the ortho- and para-quinones. Many cyclohexadienones convert to phenols.[1] In the dienone–phenol rearrangement, they convert to phenols[2] through the dienone–phenol rearrangement:[3]
The parent cyclopentadienone has only a fleeting existence under laboratory conditions, otherwise it dimerizes. The substituted derivative tetraphenylcyclopentadienone is however robust solid.[4]