C60-Fused Ketoamides Formation in Self-Sensitized Photo-Oxidation of 2-Fulleropyrrolines and Its Dynamic Study

Given the immense and potential applications in materials science and biological science, fullerenes and their derivatives have attracted extensive attention.1 A large number of chemical reactions have been developed to functionalize the fullerenes.2 In the past two decades, transition-metal-catalyzed C-H activation reaction has become one of the important strategies in the preparation of multifunctional and composite material.3 Most of its reactions use directing groups to form C60-fused heterocycles or C60-fused carbocycles, such as fulleropyrrolines,4 fullerotetrahydropyridazines,5 fulleroindolines,6 C60-fused dihydrofuran7 and C60-fused dihydrophenanthrenes8 and so on. Fulleropyrrolines are a kind of important fullerene derivative, which may have promising applications in designing and synthesizing novel organic photovoltaic materials due to the heterocyclic ring bearing a C=C bond, which can be utilized to construct a series of completely conjugated donor-acceptor (D-A) systems. Thus, it is still a demand to develop more practical approach to prepare fulleropyrrolines.9 We have recently investigated the palladium-catalyzed N-heteroannulation reaction of C60 with benzoyl hydrazone esters and unexpectedly synthesized N-unsubstituted 2-fulleropyrrolines. Notably, investigation of these reactions resulted in our discovery of the photo-oxidation of 2-fulleropyrrolines through enamine C=C bond cleavage to yield the corresponding dicarbonyl fullerene derivatives. Foot et al first reported the self-sensitized photooxidation of the C60-fused cycloadducts.10 Komatsu et al described the photochemical reaction of the open-cage fullerene derivative with singlet oxygen.11 Kabe et al also developed the synthesis of ring orifice in open-cage fullerenes by photooxygenation of azafulleroid.12 Nevertheless, the photo-oxidation of 2-fulleropyrrolines have never been explored. Herein, the self-sensitized photo-oxidation of 2-fulleropyrrolines was first discovered under very mild condition to yield a ketoamides fullerene derivative in high yields. The reaction kinetics of this self-sensitized photo-oxidation has been explored, which indicating that this photo-oxidation process is a first-order reaction and possessing low reaction activation energy (2.79 KJ/mol). Moreover, a possible mechanism related to the observed products was proposed Reference: For general reviews, see: (a) Guldi, D. M.; Illescas, B. M.; Atienza, C. M. Chem. Soc. Rev. 2009, 38, 1587. (b) Perez, E. M.; Martín, N. Chem. Soc. Rev. 2008, 37, 1512. (c) Thilgen, C.; Diederich, F. Chem. Rev, 2006, 106, 5049. (d) Nakamura, E.; Isobe, H. Acc. Chem. Res, 2003, 36, 807. (e) Diederich, F.; Gómez-López, M. Chem. Soc. Rev, 1999, 28, 263. Hirsch, A.; Brettreich, M. John Wiley & Sons, 2006. (a) Neufeldt, S. R.; Sanford, M. S. Org. Lett, 2009, 12, 532. (b) Stowers, K. J.; Sanford, M. S. Org. Lett, 2009, 11, 4584. (c) Deprez, N. R.; Sanford, M. S. J. Am. Chem. Soc, 2009, 131, 11234. (d) Desai, L. V.; Stowers, K. J.; Sanford, M. S. J. Am. Chem. Soc, 2008, 130, 13285. Wu J.; Liu, C.-X.; Wang, H.-J.; Li, F.-B.; Shi, J.-L.; Liu, L.; Li, J.-X.; Liu, C.-X.; Huang, Y.-S. J. Org. Chem, 2016, 81, 9296. Jiang, S.-P.; Liu, Z.; Lu, W.-Q.; Wang, G.-W. Org Chem Front. 2018, 5, 1188. Zhu, B.; Wang, G.-W. J. Org. Chem, 2009, 74, 4426. Yan, Y.-T.; Gao, W.; Jin, B.; Peng, R.-F.; Chu, S.-J. J. Org. Chem . 2018, 83, 672. Zhou, D.-B.; Wang, G.-W. Org. Lett. 2015, 17, 1260 Vail, S. A.; Krawczuk, P. J.; Guldi, D. M.; Palkar, A.; Echegoyen, L.; Tomé, J. P. C.; Fazio, M. A.; Schuster, D. I. Chem. - Eur. J. 2005, 11, 3375. 10 (a) Zhang, X.-J.; Romero, A.; Foote, C. S. J. Am. Chem. Soc. 1993, 115, 11024. (b) Zhang, X.-J.; Foote, C. S. J. Am. Chem. Soc. 1995, 117, 4271. (a) Murata, Y.; Komatsu, K. Chem Lett . 2001, 30, 896. (b) Murata Y, Murata M. J. Org. Chem . 2001, 66, 8187 (a) Hachiya, H.; Kabe, Y. Chem L ett . 2009, 38, 372. (b) Tanaka, T.; Nojiri, R.; Sugiyama,Y.; Sawai,.R. Org. Biomol. Chem. 2017, 15, 6136. Figure 1