Enantioselective Biginelli Reaction Catalyzed by (L)-Prolinamide Containing Imidazolium Ionic Liquid

摘要

(L)-Prolinamide containing imidazolium ionic liquids have been synthesized and evaluated as organocatalysts for the asymmetric Biginelli reaction of benzaldehydes,urea,and β-keto esters.The synthesized chiral ionic liquids were characterized by various techniques such as FT-NMR,FT-IR,TGA,and HRMS.The chiral ionic liquid containing adamantyl(L)-prolinamide having [BF4]~-anion(5 mol%)and p-toluenesulfonic acid(5 mol%)as an additive catalyzed the Biginelli reaction and afforded a variety of chiral 3,4-dihydropyrimidin-2-(1H)-ones(DHPMs)in 16-74% yields and 7-85% ee's after 48 h at room temperature and out of 30 chiral DHPMs products,18 are new.A plausible reaction mechanism and transition states or intermediates have been proposed and supported by FT-NMR spectroscopy and DFT calculations.The asymmetric induction was favored by the Re-face attack on the imine bond and the Biginelli products were obtained with(R)-absolute configuration.The DFT calculations(B3LYP/631-G*)were performed to find the energy of the intermediates.