Noncovalent Bifunctional Organocatalysts: Powerful Tools for Contiguous Quaternary-Tertiary Stereogenic Carbon Formation, Scope, and Origin of Enantioselectivity
作者:Thomas C. Nugent、Abdul Sadiq、Ahtaram Bibi、Thomas Heine、Lei Liu Zeonjuk、Nina Vankova、Bassem S. Bassil
DOI:10.1002/chem.201103005
日期:2012.3.26
observed. Using racemic α‐branched aldehydes, two contiguous (quaternary–tertiary) stereogenic centers can be formed in high diastereo‐ and enantiomeric excess (eight examples) via an efficient in situ dynamic kinetic resolution, solving a known shortcoming for maleimide electrophiles in particular. The method is of practical value, requiring only 1.2 equiv of the aldehyde, a 5.0 mol % loading of each catalyst
依靠商业上可买到的催化剂构件的组装,已经实现了具有无与伦比的底物多样性的高度立体控制的季碳(所有碳取代的)形成。例如,三组分催化剂体系的原位组装允许将α-支链醛加成到硝基烯烃或马来酰亚胺亲电试剂中(Michael产品),而将α-支链醛加成可以得到曼尼希反应产物。观察到非常高的收率,在18个实例中,有15个实例的96-99%ee被观察到。使用外消旋的α-支链醛,可以通过高效的原位动态动力学拆分在高非对映异构体和对映体过量(八个实例)中形成两个连续的(四级-三级)立体中心,尤其是解决了已知的马来酰亚胺亲电试剂的缺点。该方法具有实用价值,仅需要1.2当量的醛,每种催化剂组分的负载量为5.0 mol%,例如O- t Bu- L-苏氨酸(O- t Bu- L- Thr),磺酰胺,DMAP或O-吨BU-大号-Thr,KOH,和室温下的反应。作为亮点,乙基异戊醛(7公开了添加),提供迄今已知的最拥挤的含