A dienone is a class of organic compounds with the general formula (R2C=CR)2C=O, 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.
The parent member is divinyl ketone. It is a colorless liquid (b.p. 38-40 °C) that tends to polymerize upon standing. [1]
Dienones can arise via tautomerism of 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. [2] In the dienone–phenol rearrangement, they convert to phenols.: [3] [4] 
The parent cyclopentadienone has only a fleeting existence under laboratory conditions, otherwise it dimerizes. The substituted derivative tetraphenylcyclopentadienone is however robust solid. [5]