Evidence That Protons Can Be the Active Catalysts in Lewis Acid Mediated Hetero-Michael Addition Reactions
作者:Tobias C. Wabnitz、Jin-Quan Yu、Jonathan B. Spencer
DOI:10.1002/chem.200305407
日期:2004.1.23
mechanism of Lewis acid catalysed hetero-Michael addition reactions of weakly basic nucleophiles to alpha,beta-unsaturated ketones was investigated. Protons, rather than metal ions, were identified as the active catalysts. Other mechanisms have been ruled out by analyses of side products and of stoichiometric enone-catalyst mixtures and by the use of radical inhibitors. No evidence for the involvement
研究了路易斯酸催化弱碱性亲核试剂对α,β-不饱和酮的杂-迈克尔加成反应的机理。质子而不是金属离子被鉴定为活性催化剂。通过分析副产物和化学计量的烯酮-催化剂混合物以及通过使用自由基抑制剂,已经排除了其他机理。没有获得有关π-烯烃-金属配合物或羰基-金属-离子相互作用的证据。在非配位碱2,6-二叔丁基吡啶的存在下,反应没有进行。获得了良好的催化活性与阳离子水解常数的相关性。一羰基和二羰基底物的不同反应性已得到合理化。建立了一种用于评估质子生成的(1)H NMR探针,并且根据路易斯酸在有机溶剂中的水解倾向对其进行了分类。研究了氮,氧,硫和碳亲核试剂的布朗斯台德酸催化共轭加成反应,并讨论了不对称路易斯酸催化的意义。