Enantioselective Aza-Henry Reaction with an <i>N</i>-Sulfinyl Urea Organocatalyst
作者:MaryAnn T. Robak、Monica Trincado、Jonathan A. Ellman
DOI:10.1021/ja075653v
日期:2007.12.1
simultaneously acidify the urea and provide asymmetric induction in hydrogen-bond-catalyzed reactions. The utility of this new catalyst structure is demonstrated by the high selectivity provided in the aza-Henryreaction not only for aromatic N-Boc imine substrates but also for aliphatic imines for which enantioselective H-bonding catalysis has not previously been demonstrated.
Bifunctional asymmetric phase-transfercatalysts bearing multiple hydrogen-bonding donors have rarely been explored. The first quaternary ammonium type of these catalysts derived from cinchona alkaloids were readily prepared and found to be highly efficient catalysts for asymmetric nitro-Mannichreactions of amidosulfones. Compared with previous reports, very broad substrate generality was observed
ammonium chlorides to provide the corresponding aza-Henry adducts in good yields and very high selectivities. It represents the first general enantioselectiveaza-Henry method for azomethines derived from enolizable aldehydes, giving rise to enantiomeric excesses above 94%. In addition, the reactions with nitroethane afforded high diastereo- and enantioselectivities (syn:anti up to 95:5; up to 98% ee for syn)
作者:Chun-Jiang Wang、Xiu-Qin Dong、Zhi-Hai Zhang、Zhi-Yong Xue、Huai-Long Teng
DOI:10.1021/ja803538x
日期:2008.7.1
Highly anti-selective and enantioselective nitro-Mannich reactions have been achieved for a broad spectrum of substrates catalyzed by chiral bifunctional multiple hydrogen-bonding-donor amine-thioureas. Multiple hydrogen-bonding donors play a significant role in accelerating reactions and improving yields, diastereoselectivities, and enantioselectivities.