Tether‐Directed Regioselective Synthesis of an Equatorial_face Bisadduct of Azafullerene Using Cyclo‐[2]‐octylmalonate

Abstract

Bisazafullerene (C59N)2 has been functionalized under aerobic conditions with cyclo‐[2]‐octylmalonate through a Mannich‐type reaction, furnishing the corresponding monoadduct. A regioselective tether‐directed Bingel cyclopropanation reaction was then carried out on the azafullerene core to yield a single bisadduct. Spectroscopic analysis of the formed bisadduct showed it to have a C1 symmetrical structure, making it inherently chiral. Single‐crystal X‐ray analysis revealed the addition pattern of the azafullerene bisadduct to be equatorialface. Examination of the optical properties showed the evolution of new absorption bands, which can be used as signatures for the characterization of equatorialface bisadducts of C59N. Finally, redox assays showed that the LUMO level of the equatorialface bisadduct was increased compared to that of the parent (C59N)2.

First Synthesis of the Inherently Chiral Trans‐4′ Bisadduct of C59N Azafullerene by Using Cyclo‐[2]‐dodecylmalonate as a Tether

“…The formation of a major C 59 N‐based product was clearly observed, which was isolated in 25 % yield by column chromatography on SiO 2 . In contrast to the clean and completely regioselective synthesis of the e face bisadduct, [26] in this case, minor quantities of other bisadducts (according to MALDI TOF measurements) were also formed during the reaction, however, their separation and characterization were not possible. In addition, the formation of products derived from intermolecular Bingel cyclopropanation was not observed.…”

“…The use of phosphazene base P 1 ‐ t ‐Bu [ tert ‐butylimino‐tris(dimethylamino)phosphorane] instead of DBU led to the same observation. Halogenation of the α ‐carbon atom was previously observed during the fivefold cyclopropanation of an adamantyl derivative of C 59 N with diethyl bromomalonate [21] and in our recent report on the synthesis of the e face bisadduct [26] . Τo this end, in separate experiments, we treated bisadduct (±)‐ 3 with DBU or phosphazene base P 1 ‐ t Bu in the presence of I 2 , in dichloromethane solvent.…”

“…Inspired by the completely regioselective synthesis of the e face bisadduct of C 59 N using cyclo ‐[2]‐octylmalonate as tether, [26] we targeted this time a trans addition pattern, which has never been reported in the literature. Considering the regioselective synthesis of the trans ‐3 bisadduct of C 60 by using cyclo ‐[2]‐dodecylmalonate [28] as tether, we employed this specific macrocycle in our investigation.…”

“…In line with our approach for the synthesis of the e face bisadduct, [26] we used the free malonate moiety in 2 and performed an intramolecular Bingel cyclopropanation reaction on the azafullerene core, under high dilution conditions and by using DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ene) as base and I 2 as halogenating reagent (Figure 2b). The pronounced solubility of monoadduct 2 in non‐aromatic solvents allowed us to carry out this reaction in dichloromethane, and its progress was monitored by TLC.…”

“…Bisazafullerene (C 59 N) 2 remains the most handy heterofullerene, easily prepared by common organic synthesis routes in sufficient amounts for further derivatization [25] . We, recently, reported the first regioselective synthesis of the inherently chiral equatorial face ( e face ) bisadduct of C 59 N (Figure 1c), employing cyclo ‐[2]‐octylmalonate as tether in a Mannich‐type reaction followed by an intramolecular Bingel cyclopropanation [26] . In this work, we explore the first regioselective synthesis of the trans‐ 4 bisadduct of C 59 N utilizing cyclo‐ [2]‐dodecylmalonate as tether and we complementary investigate the impact of the bisaddition pattern on the structural, photophysical and electrochemical properties of the new material.…”