AbstractThe search for efficient and selective methods for the divergent synthesis of multi‐substituted aminotetralins is of much interest and importance. We report herein for the first time the diastereoselective [4+2] annulation of 2‐methyl aromatic aldimines with alkenes via benzylic C(sp3)−H activation by half‐sandwich rare‐earth catalysts, which constitutes an efficient route for the divergent synthesis of both trans and cis diastereoisomers of multi‐substituted 1‐aminotetralin derivatives from readily accessible aldimines and alkenes. The use of a scandium catalyst bearing a sterically demanding cyclopentadienyl ligand such as C5Me4SiMe3 or C5Me5 exclusively afforded the trans‐selective annulation products in the reaction of aldimines with styrenes and aliphatic alkenes. In contrast, the analogous yttrium catalyst, whose metal ion size is larger than that of scandium, yielded the cis‐selective annulation products. This protocol features 100 % atom‐efficiency, excellent diastereoselectivity, broad substrate scope, and good functional group compatibility. The reaction mechanisms have been elucidated by kinetic isotope effect (KIE) experiments and the isolation and transformations of some key reaction intermediates.
摘要寻找多取代氨基四氢萘分歧合成的高效和选择性方法非常重要。我们在此首次报道了半三明治稀土催化剂通过苄基 C(sp3)-H 活化 2-甲基芳香醛与烯烃的非对映选择性[4+2]环化反应,这为从容易获得的醛和烯烃中发散合成多取代 1-氨基四氢萘衍生物的反式和顺式非对映异构体提供了一条有效途径。在醛亚胺与苯乙烯和脂肪烯的反应中,使用带有立体要求高的环戊二烯配体(如 C5Me4SiMe3 或 C5Me5)的钪催化剂只能得到反式选择性环化产物。与此相反,金属离子尺寸大于钪的类似钇催化剂则产生顺式选择性环化产物。该方案具有 100% 的原子效率、出色的非对映选择性、广泛的底物范围和良好的官能团兼容性。通过动力学同位素效应(KIE)实验以及一些关键反应中间体的分离和转化,阐明了反应机理。