Rajamanickam Suresh, Saraswat Mayank, Venkataramani Sugumar, Patel Bhisma K
Department of Chemistry, Indian Institute of Technology Guwahati North Guwahati Address Assam-781039 India
Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Mohali Sector 81, Knowledge City, Manauli SAS Nagar 140306 India
Chem Sci. 2021 Oct 27;12(46):15318-15328. doi: 10.1039/d1sc04365j. eCollection 2021 Dec 1.
An intermolecular radical based distal selectivity in appended alkyl chains has been developed. The selectivity is maximum when the distal carbon is to the appended group and decreases by moving from → → positions. In -COO- linked alkyl chains, the same distal -selectivity is observed irrespective of its origin, either from the alkyl carboxy acid or alkyl alcohol. The appended groups include esters, N-H protected amines, phthaloyl, sulfone, sulfinimide, nitrile, phosphite, phosphate and borate esters. In borate esters, boron serves as a traceless directing group, which is hitherto unprecedented for any remote C -H functionalization. The selectivity order follows the trend: 3° benzylic > 2° benzylic > 3° tertiary > to keto > distal methylene ( > > ). Computations predicted the radical stability (thermodynamic factors) and the kinetic barriers as the factors responsible for such trends. Remarkably, this strategy eludes any designer catalysts, and the selectivity is due to the intrinsic substrate reactivity.
已开发出一种基于分子间自由基的附加烷基链远端选择性。当远端碳与附加基团相连时,选择性最大,并随着从→→位置移动而降低。在-COO-连接的烷基链中,无论其来源是烷基羧酸还是烷基醇,都观察到相同的远端选择性。附加基团包括酯、N-H保护的胺、邻苯二甲酰基、砜、亚磺酰亚胺、腈、亚磷酸酯、磷酸酯和硼酸酯。在硼酸酯中,硼作为无痕导向基团,这在任何远程C-H官能化中都是前所未有的。选择性顺序遵循以下趋势:3°苄基>2°苄基>3°叔碳>酮基>远端亚甲基(>>)。计算预测自由基稳定性(热力学因素)和动力学势垒是导致这种趋势的因素。值得注意的是,这种策略无需任何设计催化剂,选择性是由于底物的固有反应性。