enediol

An enediol is a molecule containing a carbon–carbon double bond with hydroxyl groups on each of the two doubly bonded carbons. The simplest example is ethenediol (ethene-1,2-diol), HO–CH=CH–OH. In general, enediols have the motif R–C(OH)=C(OH)–R′, where R and R′ may be hydrogen or organic substituents. Because each double-bond carbon bears a hydroxyl and a hydrogen, enediols may exhibit E/Z stereoisomerism (the higher-priority substituents on each carbon are the hydroxyls).

Origins and role: Enediols are most often encountered as transient intermediates in keto–enol tautomerism and in processes that interconvert carbonyl compounds with vicinal diols. They can arise by base- or acid-catalyzed tautomerizations, oxidation-reduction steps, or in photochemical rearrangements. They are typically less stable than the corresponding carbonyl compounds and may rapidly tautomerize to 1,2-diketones or back to aldehydes/ketones.

Reactivity: As enediols, these species can act as nucleophiles at the α-position toward electrophiles or engage in further oxidation to carbonyl products. They also serve as key intermediates in some aldol-type reactions and in enzymatic processes that exploit enol or enediol chemistry.

Detection and occurrence: Enediols are usually short-lived and are detected indirectly by trapping experiments, spectroscopy, or by observing the products formed after their rapid conversion.

See also: enol, keto–enol tautomerism, enediolates, enediyne.