N-Heterocyclic carbenes (NHCs) catalyze a domino Michael addition/acylation reaction to form 3, 4-dihydrocoumarins. The reaction proceeds through addition of the NHC to an aryloxyaldehyde followed by elimination of a phenoxide leaving group, generating an enol intermediate. This transient nucleophile generated in situ performs a 1, 4-addition onto a conjugate acceptor, and the carbene catalyst is regenerated upon acylation of the ...