Synthesis Of New Chiral Imidazolium Ionic Liquid Catalyst And Application For Asymmetric Synthesis Of γ-Butyrolactones

Based on the concept of asymmetric catalysis,20kinds of imidazolium salt-basedchiral ionic liquids with different N-alkyl （R=CH₃，CH₂（CH₃）₂，CH₂CH₂CH₂CH₃，PhCH₂）and different anion（X=Cl^-、BF₄^-、PF₆^-、COOCF₃^-、SO₃CF₃^-）were designedand synthesized. The structures of new compounds were characterized by¹H NMR and¹³C NMR.The new chiral ionic liquid catalysts were used for catalyzing different substratesto stereoselectively synthesize γ-butyrolactones. The effects of N-alkyl and anion onreactions were investigated. The catalyst with n-butyl and hexafluorophosphate anionshowed good catalysis and recycle. The reaction conditions were also optimized.For the reaction of trans-cinnamaldehyde with p-methoxycarbonyl benzaldehydecatalyzed by the3-n-butyl^-1-（1R,2S,5R）-（-）-menthoxymethyl imidazoliumhexafluorophosphate（3c）, the optimum reaction conditions were as follows: t=18h,T=20°C, and the quantity of catalyst of10mol%. Under the optimum reactionconditions, the yield were64.8%, trans:cis=1:5.3, ee was21.7%. After6recycles ofthe catalyst, the yield still could reach up to59.5%.For the reaction of trans-cinnamaldehyde with p-fluoro benzaldehyde catalyzedby the catalst（3c）, the optimum reaction conditions were as follows: t=20h, T=20°C,and the quantity of catalyst of15mol%. Under the optimum reaction conditions, theyield were42.2%, trans:cis=1:2.6, ee was12.7%. After6recycles of the catalyst, theyield still could reach up to38.5%.For the reaction of trans-cinnamaldehyde with p-bromine benzaldehyde catalyzedby the catalys（t3c）, the optimum reaction conditions were as follows: t=18h, T=20°C,and the quantity of catalyst of15mol%. Under the optimum reaction conditions, the yield were55.3%, trans:cis=1:3.5, ee was15.7%. After6recycles of the catalyst, theyield still could reach up to51.5%.For the reaction of trans-cinnamaldehyde with p-methyl benzaldehyde catalyzedby the catalys（t3c）, the optimum reaction conditions were as follows: t=20h, T=20°C,and the quantity of catalyst of10mol%. Under the optimum reaction conditions, theyield were50.1%, trans:cis=1:3.8, ee was8.0%. After6recycles of the catalyst, theyield still could reach up to48.5%.For the dimerization of trans-cinnamaldehyde catalyzed by the catalyst（3c）, theoptimum reaction conditions were as follows: t=10h, T=30°C, and the quantity ofcatalyst of8mol%. Under the optimum reaction conditions, the yield were53.8%,trans:cis=1:4.3, ee was13.3%. After6recycles of the catalyst, the yield still couldreach up to51.5%.The aromatic aldehyde with the electron-withdrawing group is beneficial to thereaction. The existence of large group in the catalyst structure is also beneficial for theformation of γ-butyrolactone.In summary, it is proved that the newly prepared imidazolium chiral ionic liquidscan catalyze the annulations of α,β-unsaturated aldehyde with different aromaticaldehydes to stereoselectively synthesize γ-butyrolactones. The catalytic reaction hasregioselectivity. And the catalyst can also be recycled. It not only provides a new ideain synthesis of γ-butyrolactones but also makes a very effective way for chiral ionicliquids catalysis in other stereoselective reactions.