Chiral 2-aminobenzimidazole bifunctional organocatalysts: effect of di-CF3 and TFA on catalytic mechanisms |
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Authors: | Myungmo Lee Lei Zhang Yohan Park Hyeung-geun Park |
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Institution: | 1. Research Institute of Pharmaceutical Science and College of Pharmacy, Seoul National University, San 56-1, Sinllim-dong, Kwanak-gu, Seoul 151-742, Republic of Korea;2. College of Pharmacy, Inje University, 607 Obang-dong, Gimhae, Gyeongnam 621-749, Republic of Korea |
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Abstract: | (S,S)-trans-Cyclohexanediamine-5,7-di-CF3-benzimidazole (3b) was developed as a new chiral bifunctional organocatalyst and successfully applied to Michael addition of diethyl malonate to nitroolefins (up to 99%, 98% ee) under neutral condition. Systematic investigation on the catalytic mechanism revealed that the role of the guanidine moiety and the dimethylamine moiety in catalysts might be reversed with respect to Brønsted/Lewis acidic or basic functionalities, depending on the reaction conditions (neutral or TFA co-catalyst). Generally, di-CF3 group substituted 2-aminobenzimidazole catalysts in neutral condition and non-substituted 2-aminobenzimidazole catalysts in co-catalyst (TFA) condition give high chemical yield and enantioselectivity. |
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