Research team of Liu Tongxin and Zhang Guisheng, associate professor of Henan Normal University: N-heterocyclic carbene catalyzed [3 + 2] and [4 + 2] cycloacylation of [60] fullerenes

Introduction functionalized fullerenes are widely used in materials, energy and biomedicine Therefore, it is of great significance to develop effective methods to construct fullerene derivatives with new structures The functionalization of fullerenes is a research hotspot in the field of fullerene chemistry and organic synthesis chemistry, which has been widely concerned by chemists Recently, Liu Tongxin, associate professor of Henan Normal University, and Zhang Guisheng's research team have directly and effectively realized [3 + 2] and [4 + 2] cycloacylation of [60] fullerenes (C60) for the first time by using the polarity reversal strategy of α, β - unsaturated aldehydes catalyzed by nitrogen heterocyclic carbene (NHC) Relevant research results have been published in org Lett (DOI: 10.1021 / ACS Orglett 8b01956) Introduction to Professor Zhang Guisheng: 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, nearly 20 papers have been published in J am Chem SOC., angelw 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 Brief introduction of leading scientific research achievements: N-heterocyclic carbene catalyzes the acylation of [3 + 2] and [4 + 2] fullerenes Fullerenes can be converted into fullerene ketone derivatives by acylation These derivatives have strong electronic acceptance ability and can be used to construct fullerene based donors- At the same time, the existence of ketone group provides a powerful tool for the further transformation of fullerene ketone derivatives However, acyl group and fullerene have similar electron deficient characteristics, and direct acylation of fullerene is very difficult The only report is the hydroformylation reaction catalyzed by tetrabutylammonium decatungstate (tbadt) developed by orfanopoulos group (Fig 1a) Therefore, it is still very challenging to construct [60] fullerene acylated derivatives with various structures Recently, Liu Tongxin, associate professor of Henan Normal University and Zhang Guisheng's research team directly and effectively realized the [3 + 2] and [4 + 2] cycloacylation of [60] fullerenes with α, β - unsaturated aldehydes as raw materials through the polarity reversal strategy catalyzed by Nitrogen Heterocyclic Carbene (NHC) (Fig 1b) Figure 1 Classical acylation of fullerenes (source: Organic letters) Firstly, the author selected the catalysts, bases and oxidants of azacyclocarbene with cinnamaldehyde 1a and C60 as model substrates It was found that when azacyclocarbene a was used as catalyst, etona as base and 1,4-benzoquinone (BQ) as oxidant, the reaction was 56% The yield of the target product 2a is obtained (Table 1) Table 1 Optimization of reaction conditions (source: organicletters) Under the optimal conditions, the author examined the substrate application scope of the reaction For α, β - unsaturated aldehydes with different aryl, heteroaryl and alkyl substituents, the target compounds can be obtained in medium to excellent yields and show excellent functional compatibility Compared with electron deficient substituents, the substituents with electron rich substituents have higher reactivity, while the stereoscopic effect of substituents has no significant effect on the reaction (Table 2) Table 2 Substrate applicability of fullerene [3 + 2] cycloacylation (source: Organic letters) Then, the author took α, β - unsaturated aldehydes substituted by β - methyl as raw materials, and realized [4 + 2] cycloacylation of [60] fullerenes by activating γ - carbon Under the optimum reaction conditions of Heterocyclic Carbene B as catalyst, K3PO4 as base, 3,3 ', 5,5' - tetratert butyl-4,4 '- biphenylquinone (DQ) as oxidant, the applicability of the substrate was studied Like the above-mentioned [3 + 2] cycloacylation reaction, the [4 + 2] cycloacylation reaction still has a wide range of substrate application, good functional group compatibility, and similar substituent electronic effects (Table 3) Table 3 After the substrate applicability investigation of [4 + 2] cycloacylation of fullerenes (source: Organic letters), the author also carried out the scale-up preparation experiment of [60] fullerenes and cyclopentanone (2a) and cyclohexene ketone (4a) The experimental results show that the NHC catalytic system still maintains high catalytic efficiency in a certain amount of amplification reaction (Table 4) Table 4 Scale up preparation experiment (source: Organic letters) Finally, the author describes the possible reaction mechanism, in which NHC and α, β - unsaturated aldehydes 1 and 3 respectively produce active high enol intermediate I I-I and azodiaenol intermediate VIII, and then they react with [60] fullerenes [3 + 2] and [4 + 2] nucleophilic cycloaddition to form the expected products (Table 5) Table 5 Possible reaction mechanism (source: Organic letters) fullerene fused carbon ring compounds are widely used in the receptor materials of organic solar cells, and have good conversion efficiency The results of electrochemical analysis show that the cycloacylation products of fullerenes have similar redox potential to the classical fullerene acceptor material PCBM, indicating that the new derivatives of [60] fullerene and [60] fullerene and cyclohexanone have potential as electron acceptor materials In a word, this work developed a new polarity reversal strategy of Organic Nitrogen Heterocyclic Carbene catalysis, which directly and effectively realized [3 + 2] and [4 + 2] cycloacylation of [60] fullerenes This strategy expands the scope of fullerene functionalization and represents a new direction and strategy of molecular catalysis in fullerene chemistry The research was supported by the National Natural Science Foundation of China and Henan University Science and technology innovation talent support program The results were recently published in the organizational letters The first author of this paper is Hu Beibei, a master's degree candidate of Henan Normal University Nowadays, people and scientific research have been paid more and more attention in the 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, chembeangoapp, chembeango official microblog, CBG wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the domestic representative research group, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.