Conjugate Addition of 1,3-Dicarbonyl Compounds to Maleimides Using a Chiral C2-Symmetric Bis(2-aminobenzimidazole) as Recyclable Organocatalyst
摘要:
The recyclable chiral 2-aminobenzimidazole-derived organocatalyst if efficiently promotes the room temperature asymmetric conjugate addition of 1,3-diketones, beta-ketoesters, and malonates to maleimide and N-substituted maleimides, affording the corresponding Michael adducts in excellent yields and enantioselectivities even at gram scale.
Chiral 2-Aminobenzimidazoles as Recoverable Organocatalysts for the Addition of 1,3-Dicarbonyl Compounds to Nitroalkenes<sup>†</sup>
作者:Diana Almaşi、Diego A. Alonso、Enrique Gómez-Bengoa、Carmen Nájera
DOI:10.1021/jo9010552
日期:2009.8.21
ole organocatalysts promote the conjugate addition of a wide variety of 1,3-dicarbonyl compounds such as malonates, ketoesters, and 1,3-diketones to nitroolefins in the presence of TFA as cocatalyst in toluene as solvent at rt or 0 °C. The Michael adducts are obtained in high yield and enantioselectivity, using the chiral 2-aminobenzimidazole 7b as hydrogen-bond-mediated chiral organocatalyst. This
Chiral 2-aminobenzimidazole bifunctional organocatalysts: effect of di-CF3 and TFA on catalytic mechanisms
作者:Myungmo Lee、Lei Zhang、Yohan Park、Hyeung-geun Park
DOI:10.1016/j.tet.2011.12.021
日期:2012.2
(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 Bronsted/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. (C) 2011 Elsevier Ltd. All rights reserved.