AbstractHarnessing unconventional noncovalent interactions (NCIs) is emerging as a formidable synthetic approach in difficult‐to‐access glycosidic chemical space. C‐Glycosylation, in particular, has gained a flurry of recent attention. However, most reported methods are restricted to the relatively facile access to α‐C‐glycosides. Herein, we disclose a β‐stereoselective glycosylation of indoles by employing a phosphonoselenide catalyst. The robustness of this protocol is exemplified by its amenability for reaction at both the indolyl C‐ and N‐ reactivity sites. In contrast to previous reports, in which the chalcogens were solely involved in Lewis acidic activation, our mechanistic investigation unraveled that the often neglected flanking aromatic substituents of phosphonoselenides can substantially contribute to catalysis by engaging in π‐interactions. Computations and NMR spectroscopy indicated that the chalcogenic and aromatic components of the catalyst can be collectively exploited to foster conformational distortion of the glycal away from the usual half‐chair to the boat conformation, which liberates the convex β‐face for nucleophilic attack.
摘要利用非常规的非共价相互作用(NCIs)正在成为难以进入的糖苷
化学空间的一种强大的合成方法。最近,C-糖基化尤其受到了广泛关注。然而,大多数报道的方法仅限于相对容易地获得α-C-糖苷。在此,我们公开了利用膦酰
硒化物催化剂对
吲哚进行β-严格选择性糖基化的方法。该方案的稳健性体现在它可以在
吲哚基 C 和 N 反应位点上进行反应。与以往报道中只涉及
路易斯酸活化的
查耳酮不同,我们的机理研究发现,膦
硒化物侧翼的芳香族取代基往往被忽视,它们可以通过参与 π 相互作用而对催化作用做出重大贡献。计算和核磁共振光谱显示,催化剂中的绿成分和芳香成分可以共同促进甘
氨酸的构象畸变,从通常的半椅构象转变为船形构象,从而释放出凸β面进行亲核攻击。