N-Heterocyclic Carbene Catalyzed Intramolecular Acylation of Allylic Electrophiles

The N-heterocyclic carbene (NHC) catalyzed addition reaction has been well documented recently; however, the NHC-catalyzed substitution reaction especially the S(N)2' type reaction remains a challenge. As one of the most fundamental reaction types in organic chemistry, the S(N)2' reaction catalyzed by NHC would be a powerful tool in organic synthesis. Therefore, the first NHC-catalyzed intramolecular S(N)2' substitution reaction of aldehyde with allylic electrophiles has been developed. A variety of alpha,beta-unsaturated chromanones were obtained under a domino S(N)2' reaction and isomerization. Mechanistic experiments were conducted to confirm the nature of this S(N)2' reaction.