Liu Tongxin, associate professor of Henan Normal University and Professor Zhang Guisheng's research team: Study on the synthesis of copper catalyzed [60] fullerene and tetrahydrocyclopentadine [b] indole derivatives

As a kind of carbon molecular cluster with unique structure and properties, lead fullerenes are widely used in the fields of nano materials, photoelectric materials, biomedicine and supramolecular chemistry The functionalization of fullerenes is of great significance to improve the solubility of fullerenes, regulate their physicochemical properties, promote and expand their application in related fields, and is an important research direction of fullerene chemistry and synthetic chemistry in recent years Recently, the research team of Liu Tongxin and Zhang Guisheng, associate professor of Henan Normal University, developed the method of constructing a new type of [60] fullerene and tetrahydrocyclopentadine [b] indole derivative by the direct oxidative dehydrogenation free radical carbon cyclization catalyzed by transition metal copper salt The relevant research results were published in org Lett (DOI: 10.1021 / ACS Orglett 9b02354) Profile of Professor Zhang Guisheng, Professor of Henan Normal University, doctoral supervisor In 2002, he received his Ph.D from the school of pharmacy, Peking University From 2003 to 2006, he was a postdoctoral researcher and senior researcher in the Department of Biochemistry, School of biology, Ohio State University Since 2006, Professor Zhang has served as the leader of the innovation team of the Ministry of education, vice president of Henan Provincial Chemical Association and special professor of Henan Province, enjoying the special allowance of the State Council, and won the honors of "national excellent scientific and technological workers" and "excellent experts of Henan Province" He presided over 8 NSFC projects, 1 innovation team plan of the Ministry of education, 6 major research projects and key research projects in Henan Province In recent years, more than 100 papers have been published in SCI journals such as J am Chem SOC., chem SCI., J Med Chem., chem Comm., org Lett., J org Chem The main research direction is organic synthesis and new drug research Liu Tongxin, associate professor of Henan Normal University, master tutor In 2012, he obtained the doctor of Science degree from China University of science and technology, and entered the school of chemistry and chemical engineering of Henan Normal University in September of the same year In recent years, he has published more than 20 papers in J am Chem SOC., angel Chem Int ed., chem Comm., org Lett., J org Chem And other academic journals He presided over 2 projects of National Natural Science Foundation and 1 program of scientific and technological innovation talents support in Henan Province The main research direction is fullerene chemistry and green organic synthesis chemistry Frontier research achievements: copper catalyzed synthesis of [60] fullerenes and tetrahydrocyclopentadine [b] indole derivatives fullerenes and carbon ring derivatives have been widely used in the field of solar cells as electron acceptor materials and electron transport layer materials Therefore, the development of effective methods and strategies for the preparation of different types of fullerenes and carbon ring derivatives has attracted much attention This paper is based on the concept of functionalization of fullerenes by direct oxidative dehydrogenation using simple hydrocarbons developed by the research group (org Lett 2016, 18, 4044; org Lett 2018, 20, 4801; chem Commun 2018, 54, 13331), a new type of [60] fullerene and tetrahydrocyclopentadine [b] indole derivative (Fig 1) was efficiently constructed by the free radical carbocyclization of direct oxidative dehydrogenation catalyzed by transition metal copper salt Fig 1 Free radical carbocyclization of direct oxidative dehydrogenation catalyzed by copper salt (source: Organic letters) the author optimized the reaction conditions by taking the reaction of C60 with 2-phenyl-1h-indole as the model reaction (Table 2) The optimum reaction conditions were determined through the selection of copper salts, ligands and oxidants Under the condition of Cui as catalyst, DMAP as ligand, DTBP as oxidant, and inert gas atmosphere, the target product 2A could be obtained with 36% separation yield (67%, based on the yield of consumption C60) Table 2 Optimization of reaction conditions (source: Organic letters) Under the optimal reaction conditions, the author investigated the application scope of reaction substrate (Figure 3) For indole derivatives with substituent R 1 as aromatic ring and heteroaromatic ring, and the substrates with different electronic effects on indole, the reaction can be carried out smoothly and the target product can be obtained in medium yield; the reaction is not limited to 2-benzyl substituted indole derivatives, and the functionalized indole with substituent amino group (R 1 = NRR ') can also effectively generate the carbon cyclization reaction, with 25-52% Moreover, the reaction is also compatible with allyl substituted indole derivatives, indicating that the reaction has a wide range of substrates and good functional compatibility In addition, the scale-up experiment (1.0 mmol) of [60] fullerenes and tetrahydrocyclopentadine [b] indoles was carried out, and the yield was almost unaffected Figure 3 Substrate application study (source: Organic letters) in order to explain the reaction mechanism, the author conducted control experiments Based on the experimental results and literature research, the author speculates that the reaction mechanism is as follows (Fig 4): under the reaction condition, 1A directly oxidizes through N-H bond to generate the free radical I of nitrogen center in situ, the free radical I resonates to form the highly active free radical II of carbon center, and the free radical II is captured by fullerene to generate the free radical III of fullerene According to the characteristics of the substituent R 1, free radical III can be converted into different intermediates through oxidative dehydrogenation and / or 1,3-h migration When R 1 is aryl, heteroaryl, alkenyl and NRR ', free radical III is conducive to the formation of a stable olefinic amine intermediate IV with large delocalization, and then the intramolecular [2 + 3] cyclization produces free radical v Next, the free radical V was further oxidized to obtain the final product 2 (path a) When R 1 is h or me, free radical III is prone to undergo dehydrogenation and aromatization to species VI Then, the intermediate VI was cyclized and oxidized to methylenefullerene 3 (path B) Figure 4 Study on the reaction mechanism (source: Organic letters) Finally, the electrochemical properties of the newly obtained [60] fullerene tetrahydrocyclopentadine [b] indole derivatives were studied The analysis results show that the current fullerene derivatives have similar redox potential to the classical fullerene receptor material PCBM, indicating that the new [60] fullerene and tetrahydrocyclopentadine [b] indole derivatives have the potential to be used as electronic receptor materials To sum up, the transition metal catalyzed direct oxidative dehydrogenation free radical carbocyclization was developed, which effectively realized the synthesis of [60] fullerene and tetrahydrocyclopentadine [b] indole derivatives This method has the characteristics of high regional selectivity, good atomic economy, wide range of substrate universality and good functional group compatibility It provides an effective method for the construction of fullerene and five membered carbon rings with various structures This achievement was recently published on organizational letters (DOI: 10.1021/acs.orglett.9b02354) The experimental part of the research work was completed by graduate students Wei Juan and Ru Yifei The research was supported by NSFC, Henan University Science and technology innovation talent support program and 111 program On characters and scientific research Today, science and technology elements are increasingly valued in economic life, China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.