Mechanistic investigation of N-heterocyclic carbene and Na2CO3 cooperatively catalyzed C(sp3)-F bond activation reaction of fluoroenal

The mechanism of N-heterocyclic carbene (NHC)-catalyzed C(sp(3))-F bond activation/hetero-Diels-Alder (HDA) cascade reaction between gamma-fluoroenal and ketone was theoretically studied. The computed results show that the energy barrier involved in cleavage of the C-F bond was greatly lowered in presence of Na2CO3. Moreover, the HDA process between the dienolate and ketone was both the rate- and stereoselectivity-determining step, according to the calculations. Further investigation of the role of the catalyst indicates that the NHC lowers the energy barrier of the cycloaddition step primarily by HOMO activation of the gamma-fluoroenal.