Highly enantioselective carbene-catalyzed δ-lactonization via radical relay cross-coupling

An N-heterocyclic carbene (NHC) catalyzed enantioselective cyclisation and trifluoromethylation of olefins with cinnamaldehydes via radical relay cross-coupling in the presence of Togni reagent is reported and δ-lactones tolerated with stereogenic centers at β- and γ-positions are obtained in moderate to high yields and with high enantioselectivities. Further computational studies explain that the radical cross-coupling step is the key to determining the enantioselectivity. Energy analysis of key transition states and intermediates also provides a reasonable explanation for the difficulty of diastereoselective control. DFT calculations also reveal that the hydrogen-bonding interaction plays a vital role in the promotion of this chemistry.