Covering: up to 20153-Acylated tetramic and tetronic acids are characterized by a low pKa and are likely to be deprotonated under physiological conditions. In addition, their structure makes them excellent chelators of metallic cations. We will discuss the significance of these chemical properties with regard to the biological properties and mechanisms of action of these compounds, highlighting the importance of considering them as salts or chelates for biological purposes, rather than acids.

International audienceA focused library of chiral imidazolinium salts functionalized with urea-type hydrogen-bond donor moieties has been prepared from the chiral pool. The corresponding N-heterocyclic carbenes were evaluated as organocatalysts in three enantioselective reactions involving homoenolate intermediates generated from enals. The catalysts proved competent in enantioselective cyclopentannulation and γ-lactonization reactions, a premiere for imidazoline-based NHCs. This work conveys some new ideas and knowledge on the concepts of bifunctional enantioselective organocatalysis applied to NHCs