Substituted (E)‑2-Oxo-3-butenoates: Reagents for Every Enantioselectively-Catalyzed Reaction

α,β-Unsaturated carbonyl derivatives are suitable substrates for several reactions involving the entire CCCO fragment, the carbonyl group, or the double bond. Among them, 4- substituted (E)-2-oxo-3-butenoates (1) have a specific advantage due to the presence of a further carboxylic group attached to the carbonyl carbon atom because the resulting 1,2- dicarbonyl system may be coordinated to a Lewis acid. This coordination increases the reactivity of the substrate, and use of an asymmetric catalyst may induce enantioselectivity in the reactions. In view of the importance of these molecules in the synthesis of organic compounds, arylidene pyruvates (1, R = Ar) have been considered as worthy of a general review, starting with their syntheses, the chemical properties, and the various reactivity.