Diastereoselective synthesis of trifluoromethylated γ-butyrolactones via N-heterocyclic carbene-catalyzed conjugated umpolung of α,β-unsaturated aldehydes

The N-heterocyclic carbene-catalyzed conjugate umpolung of differently substituted alpha,beta-unsaturated aldehydes is described. Coupling of these compounds with a variety of trifluoromethylated ketones results in the selective formation of fluorinated gamma-butyrolactones. Using thiazolium-derived N-heterocyclic carbenes, the unlike stereoisomers are formed predominantly, whereas the imidazol-2-ylidene IMes results in lower selectivities and the preferred formation of the like isomer.