Regioselective acylation and carboxylation of [60]fulleroindoline via electrochemical synthesis

Abstract

A regioselective and highly efficient electrochemical method for direct acylation and carboxylation of a [60]fulleroindoline, affording 1,2,3,16-functionalized [60]fullerene derivatives, regioselectively, has been developed.

Successively Regioselective Electrosynthesis and Electron Transport Property of Stable Multiply Functionalized [60]Fullerene Derivatives

“…Fullerene Derivatives. The dianionic species of [60]fulleroindolines 1 can be obtained by controlled potential electrolysis (CPE) and have ring-opened structures after acceptance of two electrons [25,28]. For these ring-opened structures, the most negatively charged carbon atom among the fullerene skeleton is located at the para position of the aryl substituents.…”

“…Only one isomeric monocycloadduct is usually formed, up to 8 regioisomeric biscycloadducts have been isolated from cycloaddition reactions of C 60 [8]. On the other hand, the regioisomers of tetrafunctionalized C 60 derivatives reported most commonly are 1,2,3,4-isomers (A) [9][10][11][12][13][14], 1,4,11,15-isomers (B) [15][16][17][18], 1,2,4,15-isomers (C) [19][20][21][22][23], and 1,2,3,16-isomers (D) [24][25][26][27][28][29], while for the hexafunctionalized C 60 derivatives, the most frequently encountered regioisomers are 1,2,3,4,5,6-isomers (E) [30][31][32] and 1,2,4,11,15,30-isomers (F) [15][16][17][18][33][34][35] (Figure 1). Although the elegant templated multifunctionalizations of fullerenes have been devised to realize high regioselectivity [8,36], the regiocontrol on the formation of a specific isomer of biscycloadducts and multicycloadducts is still a daunting task.…”

“…The electrophilic-to-nucleophilic reactivity reversal of fullerenes and their derivatives caused by electrochemical reduction opens a new territory in fullerene chemistry and has demonstrated increasing importance in the efficient synthesis of novel fullerene derivatives [37], including the abovementioned types A, C, and D [11,19,[25][26][27][28][29]. It was interestingly found that the same dianionic [60]fulleroindoline (1a 2-, vide infra) behaved differently toward alkylating and acylating reagents.…”

“…It was interestingly found that the same dianionic [60]fulleroindoline (1a 2-, vide infra) behaved differently toward alkylating and acylating reagents. For example, the reaction of 1a 2with benzyl bromide gave both mono-and dibenzylated 1,2,3,16adducts [25], while its reaction with benzoyl chloride could afford only monoacylated 1,2,3,16-adducts [28]. The attempted synthesis of diacylated 1,2,3,16-adducts failed and remains challenging.…”

“…Even though we could capture the intermediate leading to the cyclized 1,2,4,17-adduct, the instability of this unique cyclized product precluded its characterization by 13 C NMR and single-crystal X-ray analysis. Bearing the aforementioned different reactivity of the same dianionic species toward alkylating and acylating reagents and instability of the previously obtained tetrafunctionalized product in mind, our continuous efforts in electrochemical functionalization of fullerene derivatives [25,28,29,[38][39][40][41] stimulated us to investigate the reaction of the dianionic [60]fulleroindolines 1a-c 2-with phthaloyl chloride in order to contrast their reactivity behavior and to see if the unprecedented tetrafunctionalized cis-3 ′ isomers (type G) and "S"-shaped hexafunctionalized products (type H) bearing two acyl groups can be generated in the present case [42]. It turns out that these two unique types of tetra-and hexafunctionalized products can be successfully synthesized and are stable up to 107−275°C.…”