Abstract

Proton transfer processes mediate many organic reactions. How to realize stereochemical control of this process has always been a challenging topic in the field of asymmetric catalysis. In this study, N-(diphenyl­methyl)-1-phenylethan-1-imine (Schiff base derived from 2,2-diphenylethan-1-amine and acetophenone) was used as substrate, and different near neutral solvents and various chiral metal complex catalysts were used to carry out photoinduced C=N double bond transfer in the substrate under irradiation with a mercury ultraviolet lamp. The double bond transfer in the substrate molecule was highly selective. Solvents containing strong electronegative atoms like oxygen and chlorine, such as alcohols, aldehydes, and carbon tetrachloride, were more effective than other solvents under high light intensity. The 1,3-proton transfer process involves photo­excitation of the Schiff base and coordination of the latter to the central metal atom of the chiral catalyst, so that the substrate molecule is placed in a stable chiral environment to form a transition state. The strongly electro­negative atom of the near-neutral solvent attracts the active α-hydrogen from the excited Schiff base molecule to form a negatively charged delocalized π-bond structure. The subsequent proton addition yields more stable molec­ular structure to complete the selective proton transfer process. Among the examined chiral catalysts, divalent tin porphyrin was the most effective, and the product yield and enantiomeric excess were 98% and 91.49%, respectively. The described photoinduced C=N double bond transfer in N-(diphenylmethyl)-1-phenyl­ethan-1-imine is characterized by mild conditions (room temperature), high stereoselectivity, and simple operation.

中文翻译：

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N-（二苯甲基）-1-苯基乙-1-亚胺中的选择性氢转移

摘要

质子转移过程介导许多有机反应。在不对称催化领域，如何实现该过程的立体化学控制一直是一个具有挑战性的话题。在这项研究中，N-（二苯基甲基）-1-苯基乙-1-胺（由2,2-二苯基乙-1-胺和苯乙酮衍生的席夫碱）作为底物，并使用不同的近中性溶剂和各种手性金属络合物催化剂进行反应。在汞紫外线灯的照射下，在基材中光诱导的C = N双键转移。底物分子中的双键转移是高度选择性的。在高光强度下，含有强负电性原子（如氧和氯）的溶剂（如醇，醛和四氯化碳）比其他溶剂更有效。1,3-质子转移过程涉及席夫碱的光激发和席夫碱与手性催化剂中心金属原子的配位，从而将底物分子置于稳定的手性环境中以形成过渡态。中性溶剂的强负电性原子从被激发的席夫碱分子吸引活性α-氢，形成带负电荷的离域π键结构。随后的质子添加产生更稳定的分子结构，以完成选择性质子转移过程。在所研究的手性催化剂中，二价锡卟啉最为有效，产物收率和对映体过量分别为98％和91.49％。所述的光诱导的C = N双键转移 随后的质子添加产生更稳定的分子结构，以完成选择性质子转移过程。在所研究的手性催化剂中，二价锡卟啉最为有效，产物收率和对映体过量分别为98％和91.49％。所述的光诱导的C = N双键转移 随后的质子添加产生更稳定的分子结构，以完成选择性质子转移过程。在所研究的手性催化剂中，二价锡卟啉最为有效，产物收率和对映体过量分别为98％和91.49％。所述的光诱导的C = N双键转移N-（二苯甲基）-1-苯基乙-1-胺的特征在于温和的条件（室温），高的立体选择性和简单的操作。