Experimental Exploration Of The Stereoselectivity Of Counter Anion-Directed Nucleophilic Addition Reaction Of Iminium Salts

Iminium ion can be regarded as protonation or alkylation products of imine. It is a class of positive ions with general formular [R1R2C=NR3R4]+Iminium ions are easily generated by the condensation of amines with carbonyl compounds. Iminium salts are more electrophilic than the corresponding aldehydes or ketones. For this reason, the reversible formation of the iminium salt activates the carbonyl component toward nucleophilic attack.The organocatalytic asymmetric reations based on iminium activation is one of the youngest subfields of organocatalysis. Iminium activation is a completely new asymmetric catalytic mechanism, which has been widely used in the fields of the asymmetric cycloaddition reactiona,1,4-nucleophilic addition,1,2-nucleophilic addition, asymmetric Strecker reactions.This article first introduces the asymmetric cycloaddition reaction and1,4-nucleophilic addition based on iminium activation. The recent progress on asymmetric Strecker reactions including a chiral substrate-assisted diastereo-selective and enantioselective by asymmetric catalytic is reviewed. Systematic studies into structure-activity relationships are conducted. On this basis, we introduced high enantioselectivities conferred by a chiral counterion in catalysis. According to NMR studies, anion and cation of iminium ions are not separated, but rather exist as contact ion pairs in aprotic solvents.This article we select aliphatic cyclic secondary amine piperidine, morphine and pyrrolidine with benzaldehyde are respectively condense to form iminium salts. condensed the imine salt and characterization.The structures are confirmed.Biirgi Dunitz analyze the trajectory of nucleophilic attack on a carbonyl.Nucleophiles approach the carbon and oxygen plane at an angle that is typically about1O5°±5°rather than perpendicular to the carbonyl pi system,which can be used as a model for explaining and predicting nucleophilic attack of carbonyls. From the reported crystal structure of iminium salts by X-ray diffraction, we explored interaction force between anion and cation, and the position and angle of the anion. We can conjecture whether its nucleophilic addition reaction is stereoselective, and get the desired results.