N‐Heterocyclic Carbene Catalysis as a Tool for Gaining Access to the 3,4‐Dihydropyran‐2‐one Skeleton

An overview of the progress made in the synthesis of 3,4‐dihydropyran‐2‐ones since the development of NHC catalysis is reported. Two distinct classes of species – electrophilic α,β‐unsaturated acylazolium and nucleophilic azolium enol/enolate intermediates – can easily be produced from different substrates through the intermediacy of NHC catalysis. They enable the construction of the 3,4‐dihydropyran‐2‐one skeleton, the core of natural and synthetic products with significant biological activities, through Michael additions, cycloadditions and rearrangements.