The Asymmetric Michael Addition And Aldol Reaction Catalysed By Cyclodextrin Derivatives

Cyclodextrin is a ring molecule composing of several?-D-pyran glucose units connected by alpha 1,4-glycosidic bond each other,it contains a hydrophobic cavity and a hydrophilic outside edge.For this reason,it can form stable molecular assembly body with organic molecules through molecular inter-atomic forces such as van der Waals force and hydrophobic interactions.The asymmetric Michael addition and Aldol reactions are the hot issues in the field of asymmetric catalysis.After decades of research,big achievements have been made in the fields of asymmetrical organocatalysis using L-proline derivatives or chiral thioureas as chiral catalysts.However,many problems are still present,which include use of big polar solvent,high loading of catalyst,and difficulty of recycling the catalysts.The traditional methods to design catalysts can not resolve these problems.By consulting the nature of cyclodextrin a novel idea will be tried to design a new catalyst,which is to synthesize series of cyclodextrin supramolecular derivatives,wishing to get a catalyst with the advantages of high efficiency and selectivity,broad applicability,low cost and reusability.Here,two thiourea groups with different configurations were linked to the?-cyclodextrin,and catalytic systems were estabilished by using the obtained?-cyclodextrin derivatives in combination with a buffer solution.The catalytic systems showed good performances in the asymmetric Michael addition of acetone with?-nitrobenzene ethylene through co-induction of the cyclodextrin cavity and chiral side chains.The catalytic systems were investigated thoroughly and optimal reaction conditions were obtained,which were 20 mol%of CD-1,2 ml of CH₃COONa/CH₃COOH buffer solution,2 ml of DMSO,and reaction temperature of 25oC.This system was also applied to the asymmetric Michael addition of acetone with various nitroolefins,and good results were also received.This catalyst could be recovered easily and recycled up to four times.Though the catalytic activity of the catalyst decreased in some degree in the catalytic run,its enatioselectivity almost maintained.The chiral cyclohexane-1,2-diamine was linked to?-cyclodextrin to assemble a new type of supramolecular system for catalytic asymmetric Aldol addition.It catalyzes the reaction of cyclopentanone and nitrobenzaldehyde through co-induction of the cyclodextrin cavity and chiral side chains.The final optimized conditions obtained through series experiments were:10 mol%CD-5,2 ml of CH3COONa/CH3COOH buffer solution?pH=4.8?,and reaction temperature of 25oC.In addition,this system was also applied to the Aldol reactions of cyclopentanone and various aromatic aldehydes,and good results were received.This catalyst could be recovered easily and recycled up to five times.Though the catalytic activity of the catalyst decreased in some degree in the catalytic run,its enatioselectivity almost maintained.