All-Carbon [4+2] Cycloaddition Catalyzed by an NHC

Significance

The first all-carbon [4+2] cycloaddition catalyzed by an N-heterocyclic carbene has been reported. A variety of α,β-unsaturated acid fluorides 2 and silyl dienol ethers 3 react to give 1,3-cyclohexadienes 4 in good to high yields with complete diastereocontrol. Mechanistic investigations support a concerted process with strong preference for endo orientation of the coupling partners. Use of cyclic dienolates proved crucial for the success of the reaction as acyclic or aldehyde-derived dienolates delivered O-acylation products.