Research team of Liu Tongxin and Zhang Guisheng, associate professor of Henan Normal University: palladium catalyzed series coupling of three components − carbon cyclization to synthesize polysubstituted [60] fullerene cyclopentane derivatives

Introduction fullerenes and their derivatives are a kind of carbon nanomaterials with unique molecular structure and physicochemical properties, which are widely used in organic electronics, biomedicine, supramolecular chemistry and polymer chemistry Chemical functionalization plays an important role in improving and regulating the physical and chemical properties of fullerenes, creating and enriching fullerene based carbon materials, promoting and expanding the application of fullerenes in different fields Therefore, functionalization plays an important role in fullerene chemistry and has become an important research direction in fullerene chemistry and organic synthesis chemistry Recently, Liu Tongxin, associate professor of Henan Normal University and Zhang Guisheng's research team reported the first case of transition metal catalyzed multi-component carbon cyclization of [60] fullerenes Under the catalysis of PD (PPH 3) 4, [60] fullerenes, dienyl esters and (hetero) aryl iodides undergo a series coupling − carbon cyclization process Polysubstituted [60] fullerenes and cyclopentane derivatives were synthesized regioselectively The related research results were published in org Lett (DOI: 10.1021 / ACS Orglett 9b04321) Prof 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 The main research direction is organic synthesis and new drug research So far, more than 120 papers have been published in important academic journals at home and abroad, such as J am Chem SOC., chem SCI., J Med Chem., chem Comm., org Lett., J org Chem Liu Tongxin, associate professor of Henan Normal University, master tutor In 2012, he graduated from the Department of chemistry, University of science and technology of China with a doctorate of science In the same year, he entered the school of chemistry and chemical engineering of Henan Normal University He has undertaken many research projects, such as the National Natural Science Foundation of China, the science and technology innovation talent project of colleges and universities in Henan Province, and the key science and technology research project of Henan Provincial Department of education The main research fields are fullerene chemistry and green organic synthesis chemistry So far, more than 20 research papers have been published in famous international academic journals such as J am Chem SOC., angelw Chem Int ed., chem Comm., org Lett., adv synth Catalyst., J org Chem A brief introduction to the research achievements of the research team: palladium catalyzed synthesis of [60] fullerene cyclopentane derivatives; fullerene carbon ring derivatives as electronic acceptor materials and electronic transmission materials have been widely used in the field of organic solar cells and perovskite solar cells In order to give fullerene derivatives more excellent properties, it is an important research topic to develop multi-component reactions that can easily and flexibly introduce various structural units and functional groups to prepare fullerene and carbon ring derivatives In the early stage of this research group, we developed a multi-component reaction strategy to functionalize fullerenes (chem Commun 2015, 51, 12775; chem Commun 2016, 52, 982; chem Commun 2018, 54, 13331) and prepare fullerene and carbon ring derivatives (org Lett 2016, 18, 4044; org Lett 2018, 20, 4801; org Lett 2019, 21, Based on 6461), the first transition metal catalyzed cyclization of [60] fullerenes was developed A series of polysubstituted [60] fullerenes and cyclopentane derivatives (Fig 1) have been prepared by series coupling of [60] fullerenes, dienyl esters and (hetero) aryl iodides with three components catalyzed by palladium Figure 1 Palladium salt catalyzed multicomponent carbon cyclization (source: Organic letters) the author optimized the reaction conditions by taking the reaction of C60, 2 - (2,3-propanediene-1-butyl) - dimethyl malonate and iodobenzene as model reaction (Table 2) Through the selection of palladium salt, alkali and cosolvent, the optimal reaction conditions were determined: under the condition of PD (PPH 3) 4 as catalyst, Rb 2CO 3 as alkali and air atmosphere, the target product was obtained with 34% separation yield (70%, based on the yield consuming C 60) 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 the aryl iodides with different electronic effect substituents, the reaction can be carried out smoothly and the target product can be obtained in medium to high yield, and the reaction shows excellent functional compatibility For example, bromine, aldehyde group, isothiocyan group, cyano group, ester group, nitro group and ferrocene unit are all compatible; when the reaction substrate is heteroaryl iodine compound, the reaction can also proceed smoothly Unfortunately, when the reaction substrate 2 is 2 - (2,3-propanediene-1-amyl) - dimethyl malonate 2c, 2 - (2,3-propanediene-1-butyl) - malondionitrile 2D, 2 - (phenylsulfonyl) hexane-4,5-dienoic acid methyl ester 2E, 2-nitrohexane-4,5-dienoic acid methyl ester 2F, the reaction can not be carried out or only a small amount of products can be obtained, which shows that the method still has certain limitations At the same time, the author has also carried out the amplification preparation experiment of [60] fullerene cyclopentane (1.0 mmol), and obtained the target product in almost the same yield (Fig 4) In addition, the presence of diesteryl and alkenyl in the product not only makes it have good solubility, but also provides conditions for further modification For example, product 4AA can be converted into fullerene carboxylic acid derivative 6 by hydrolysis reaction Figure 3 Study on the application scope of substrate (source: Organic letters) Figure 4 [60] amplification preparation and transformation of fullerene cyclopentane (source: Organic letters) In order to explain the reaction mechanism, the author carried out relevant control experiments On the basis of experimental results and literature research, the author speculates that the reaction mechanism is as follows (Fig 5): aryl iodides and zero valent palladium undergo oxidative addition to form intermediate I first, and I is further inserted into the alkenyl ester to form π - allyl palladium complex II with the characteristics of zwitterions In the possible reaction path path a, the carbon anion end of intermediate II directly attacks C 60 to form intermediate III, and then the final product is obtained through intramolecular cyclization However, according to the results of control experiments, the possibility of transformation going through this path to produce the final product can be ruled out In another reaction path, path B, π - allyl palladium complex II is coordinated with C60 to produce a highly active intermediate IV with fullerene positive ion characteristics, further reducing the LUMO orbit of fullerene itself, making the nucleophilic addition of carbon anion end to carbon cage easy to carry out and produce mesomer V, and further [2 + 3] cyclization of V in the molecule to obtain the target product 4 It should be noted that from the perspective of IV formation, the reaction path path B can also explain the reason why the substrate with electron withdrawing group has higher yield than that with electron supplying group Therefore, the author speculates that the reaction may have experienced the mechanism path of path B In addition, although there is the possibility of 7-membered [60] fullerenes and 3-cycloheptene derivatives generated by intramolecular [2 + 5] cyclization of intermediate V, due to the large volume and thermodynamic disadvantages of fullerenes, the reaction shows a specific regional selectivity Figure 5 Study on the reaction mechanism (source: Organic letters) Finally, the electrochemical properties of the newly obtained [60] fullerene cyclopentane derivatives were studied The results show that the redox potential of [60] fullerene cyclopentane derivatives is similar to that of PCBM, indicating that the new [60] fullerene cyclopentane derivatives have the potential to be used as electron acceptor materials In conclusion, the author has developed the first multi-component carbon cyclization of [60] fullerenes catalyzed by transition metals Polysubstituted [60] fullerenes and cyclopentane derivatives were prepared by the series coupling of [60] fullerenes, dienyl esters and (hetero) aryl iodides with three components catalyzed by palladium This method has a wide range of substrate universality and good functional group compatibility This achievement was recently published on organizational letters (DOI: 10.1021 / ACS Orglett 9b04321) The first author of this paper is Liu Qingfeng, a doctoral candidate of Henan Normal University The research was supported by NSFC, Henan University Science and technology innovation talent support program and 111 program 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 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.