α,α-Disubstituted Cyclopentenes via Desymmetrization of 1,3-Diketones

Significance

Chiral quaternary carbon centers pose a formidable challenge to synthetic organic chemists. The authors here report an approach to enantioenriched α,α-disubstituted cyclopentenes via a chiral N-heterocyclic carbene (NHC)-catalyzed aldol-decarboxylation reaction sequence. Reaction between the unsaturated aldehyde moiety of the starting material and the NHC catalyst followed by a protonation step allows for a stereoselective, intramolecular aldol reaction. The product then cyclizes to a β-lactone, which may decarboxylate to form a cyclopentene if the newly formed double bond is conjugated to an arene. In the case of aliphatic ketones the driving force for this step is too weak and the reaction stops at the β-lactone stage. The yields obtained are good with high to excellent enantioselectivities.