Enediols are alkenes with a hydroxyl group on each carbon of the C=C double bond. Normally such compounds are disfavored components in equilibria with acyloins.  One special case is catechol, where the C=C subunit is part of an aromatic ring.  In some other cases however, enediols are stabilized by flanking carbonyl groups. These stabilized enediols are called reductones.  Such species are important in glycochemistry, e.g., the Lobry de Bruyn-van Ekenstein transformation.
Ribulose-1,5-bisphosphate is a key substrate in the Calvin cycle of photosynthesis.  In the Calvin cycle, the ribulose equilibrates with the enediol, which then binds carbon dioxide.  The same enediol is also susceptible to attack by oxygen (O) in the (undesirable) process called photorespiration.