Ionic Liquids Derived From L-prolinol Catalyzed Asymmetric Michael Addition

Michael addition is a very important reaction to form C-C bond in organic synthesis. Asymmetric Michael addition is more important. So the research of catalytic asymmetric Michael addition is one of essential study issues in the field of asymmetric synthesis recently. Organocatalysts without metal has been attached great importance in the field of catalytic reaction for their particular advantage. L-prolinol derivates are important proportion of organocatalysts.However, when L-prolinol derivates are used as catalyst, there are some defects, such as: the great amounts of application, the difficulty for recycling, and the narrow application range. For the particular properties of ILs, there will be some particular effects when quaternary ammonium groups are introduced into L-prolinol derivates, which is studied in this paper.The primary works of this paper is to synthesize a series of functionalized chiral ionic liquids derived from L-prolinol. The starting material was (S)-(2-hydroxymethyl)- pyrrolidine which was purchased by the reagent company. After reacting with benzyl carbonochloridate, Cbz protected L-prolinol was obtained. When Cbz protected L- prolinol reacted with methanesulfonyl chloride, (S)-benzyl-2-((methylsulfonyloxy)- methyl)pyrrolidine-1-carboxylate was produced. After treatment with LiBr, (S)-benzyl 2-(chloromethyl)-pyrrolidine-1-carboxylate was obtained which could converted into (S)-benzyl 2-((dimethylamino)methyl)pyrrolidine-1-carboxylate when stirred with Me2NH. Then reacted with halohydrocarbon could give the corresponding quaternary alkylammonium. When reacted with H2 catalysed by Pd-C, the Cbz- protection was removed and the target compounds were afforded. When ionic liquids were preparing, the stability of Cbz- or Boc- protected L-prolinol derivatives was studied, which was helpful for synthesis of L-prolinol derivatives.Next, the catalytic effects of those ionic liquids on the Michael addition of cyclohexanone to trans-nitrostyrene were investigated. The highest reaction yield was 92 %, and the stereoselectivity was excellent for the highest syn/anti was 99:1 and the highest ee was 99 %. A plausible transition state was proposed to explain the stereochemical results, and the structure-activity relationship of catalysts was studied. Those catalysts could easily be recovered to reuse for two times with similar yield and selectivity. When those catalysts were used to catalyze Michael addition of cyclohexanone to Derivate of trans-nitrostyrene, they showed preferable results.