Diastereospecific and Highly Site-Selective Functionalization of C₇₀ Fullerene by a Reaction with Diethyl N-Arylaziridine-2,3-dicarboxylates

Abstract

The diastereospecific and highly site-selective cycloaddition of N-arylazomethine ylides generated in situ from diethyl N-arylaziridine-2,3-dicarboxylates to C70 fullerene is reported. The reaction provides C70 fulleropyrrolidines in up to hundreds on a milligram scale as α- and β-adducts in a 4:1 ratio with a controlled stereochemical outcome: cis-aziridines give exclusively trans-adducts, and trans-aziridines give only cis-adducts. The 1H and 13C­{1H} NMR spectra for different isomeric adducts were recorded and analyzed to identify some characteristic features, which permit an easy identification of isomeric adducts of this type.

Controlling the Charge Transfer Mechanism and Efficiency by Means of Different C70 Regioisomeric Adducts

“…1 H NMR spectra of the products reveal the fingerprints of the individual isomers. [ 35 ] These are singlets of pyrrolidine protons at 5.66 and 5.95 ppm for DL1 and 5.82 and 6.15 ppm for DL2 , from which we conclude that they are the cis ‐β and cis ‐α isomers, respectively. Their absorption spectra, in which only the DL1 isomer shows an absorption maximum typical for cis ‐β isomers, further support our assignment.…”

“…An addition of the N ‐arylaziridine‐2,3‐dicarboxylates to fullerene C 70 , described previously, [ 35 ] was used for the construction of C 70 conjugates with meso ‐tetraphenylporphyrin (TPP). However, an attempted addition of porphyrinic aziridine 1 with carboxyethyl moieties ( Figure a), in contrast to previously report for C 60 , [ 46 ] affords totally insoluble products, which led us to introduce solubilizing groups.…”

“…According to the literature, the addition of such aziridines to fullerenes processes as a sequence of concerted stages of aziridine ring opening and 1,3‐dipolar cycloaddition with extremely high stereospecificity, while the addition of cis ‐aziridine affords only trans ‐adducts. [ 35,47 ] In principle, monoaddition to C 70 may afford four different position regioisomers, so‐called site‐isomers. Practically, the reaction mixtures consist of two isomers, namely, a major “α” [1,9] adduct and a minor “β” [7,8] adduct.…”

“…Diethyl ether “extra dry” was used as received. C 70 adducts C 70 ‐H , C 70 ‐CH 3 , and C 70 ‐Br , [ 35 ] TPP, [ 65 ] and 5‐(4‐aminophenyl)‐10,15,20‐triphenylporphyin, [ 66 ] octyl glyoxylate, [ 67 ] and octyl diazoacetate [ 68 ] were synthesized as described in the literature.…”

“…[ 33 ] In addition to the more challenging functionalization, [ 34 ] larger fullerenes such as C 70 show lower symmetry, which also leads to a larger number of position regioisomers, as well as higher costs. [ 32,35 ] The two major regioisomers of C 70 monoadducts are its α‐ and β‐regioisomers, which disclose, however, no notable differences in terms of their reduction. As a matter of fact, larger fullerenes have attracted much less attention, even though they are considered promising structures for the conversion of photochemical energy into storable energy forms.…”