Imidazolium chiral ionic liquid derived carbene-catalyzed conjugate umpolung for synthesis of γ-butyrolactones

A serial of imidazolium chiral ionic liquids starting from commercially available (-)-menthol as a chiral pool have been synthesized and successfully used for catalyzing conjugate umpolung of alpha,beta-unsaturated aldehydes to stereoselectively synthesize gamma-butyrolactones. The catalytic activities of these ionic liquids are examined and compared. The reaction of trans-cinnamaldehyde and rho-methoxycarbonyl benzaldehyde as a model has been investigated in detail, and the reaction conditions have been optimized. Under the selected conditions, the ionic liquid catalyst can catalyze the annulations of trans-cinnamaldehyde with different aromatic aldehydes to afford differently substituted gamma-butyrolactones. The recyclability of the ionic liquid catalyst is investigated, and the results have indicated that the catalyst can be recycled six times without obvious activity decreasing.