N-heterocyclic carbene cascade catalysis: Dual Bronsted/Lewis base rearrangement of cyclopropyl enol esters to dihydropyranones

The first example of Bronsted/Lewis base cascade catalysis using an N-heterocyclic carbene has been realised through the rearrangement of cyclopropyl esters to dihydropyranones. The scope and mechanism of this transformation has been examined implicating a novel NHC-mediated electrocyclic cyclopropane rearrangement followed by an anionic oxy Claisen-rearrangement.