The Mechanism Study Of CF₃-Containing Imidazolidine For Asymmetric Syn-Selective Cross-Aldol Reaction Of Hydroxyacetone

Formation of new carbon-carbon bonds, is always an everlasting topic oforganic chemistry. In past decade, the selective organic reactions attract considerableattention. A milestone in the evolution of aldol chemistry, direct asymmetric aldolreaction, is undoubtedly one of the most versatile C-C bond forming reactions inconstructing chiral molecules with promising reaction （atom, step and redox）economies.A novel CF₃-containing imidazolidine （2R,4S）-4-benzyl-1,2-dimethyl-2-（trifluoromethyl）imidazolidine was designed and synthesized from methyl L-phenylalanine methyl ester hydrochloride. Its absolute conformation was confirmed byNMR analysis: HMQC and NOE.This compound was explored in asymmetric reactions, and application in thedirect aldol reaction of-hydroxylacetone with a wide range of aldehydes providedsyn-1,2-diols in high regio-and enantio-selectivities.19F NMR analysis was employed to study the mechanism of this reactionsystem. To our surprising, we found that a part of this CF₃-containing imidazolidinedecomposed into （S）-N1-methyl-3-phenylpropane-1,2-diamine and1,1,1-trifluoroacetone.42%of CF₃-containing imidazolidine was detected when thereaction was over after48h-96h. Both of diamine and imidazolidine could catalyzethe aldol reaction of hydroxyacetone with aldehydes.According to the results, we proposed the transition state of-hydroxylacetonewith aldehydes. In the reaction of-hydroxylacetone with CF₃-containingimidazolidine products form via a reaction involving Z-enamine. And calculationchemistry confirmed Z-enamine is the preffered configuration.