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 SN2′ type reaction remains a challenge. As one of the most fundamental reaction types in organic chemistry, the SN2′ reaction catalyzed by NHC would be a powerful tool in organic synthesis. Therefore, the first NHC-catalyzed intramolecular SN2′ substitution reaction of aldehyde with allylic electrophiles has been developed. A variety of α,β-unsaturated chromanones were obtained under a domino SN2′ reaction and isomerization. Mechanistic experiments were conducted to confirm the nature of this SN2′ reaction.