Highly Efficient Retro-cycloaddition Reaction of Isoxazolino[4,5:1,2][60]- and -[70]fullerenes

Abstract

Isoxazolino[4,5:1,2][60]- and -[70]fullerenes undergo an efficient retro-cycloaddition reaction to pristine fullerene by thermal treatment in the presence of an excess of a dienophile and Cu(II) catalysis, which can be selectively used in the presence of malonate or pyrrolidine cycloadducts. Trapping experiments using N-phenylmaleimide as dipolarophile have shown that the reaction mechanism occurs by thermal removal of the nitrile oxide 1,3-dipole, in a process which is favored by the presence of Cu(II) as the catalyst. The ESI-MS study supports the observed retro-cycloaddition process for both C60 and C70 derivatives. In contrast to previous electrochemical retro-cycloaddition processes observed in fulleropyrrolidines, isoxazolinofullerenes were stable under oxidative conditions.

Mass Spectrometry Studies of the Retro-Cycloaddition Reaction of Pyrrolidino and 2-Pyrazolinofullerene Derivatives Under Negative ESI Conditions

“…In this case, with comparable intensity to [C 60 ] + , a fragment at m/z 752 corresponding to [C 60 S] + was also found [41]. Similar results are found in the ESI-MS/MS spectra in positive mode from fullerene fused to heterocyclic rings containing oxygen atoms such as isoxazolinofullerenes (also two heteroatoms in the heterocyclic moiety), which fragment leading to a fragment [C 60 O+H] + [25]. In contrast, an analogous fragment [C 60 NH+H] + is not observed in the MS/MS mass spectra of nitrogen containing heterocyclic fullerenes.…”

“…Because C 60 acts as an electron poor olefin, the cycloaddition reaction with azomethine ylides leads to the formation of pyrrolidinofullerenes [22,23] while the dipolar cycloaddition of nitrile imines affords the corresponding pyrazolinofullerenes [24]. During the course of our investigations on the homo-and heterocyclic fullerene cycloadducts, we have observed that the molecular odd-electron ions generated under ESI conditions and negative mode of detection from substituted isoxazolinofullerenes [25] . On the other hand, the retro-Diels-Alder reaction (RDA) is a wellknown process, which can be generated in a mass spectrometer [26][27][28], and is one of the most investigated spectrometric process in the fullerene chemistry [29][30][31].…”

Cycloaddition Reactions of Butadiene and 1,3‐Dipoles to Curved Arenes, Fullerenes, and Nanotubes: Theoretical Evaluation of the Role of Distortion Energies on Activation Barriers

“…[13][14][15] C 60 reacts with different nitrile oxides forming [6,6]fullerene-isoxazolines, where in this case the retro-cycloaddition was also possible. [16][17][18] There are no experimental results for the addition of simple nitrones to fullerenes as they are very unstable; however, the addition of N-silyloxynitrones to C 60 has been investigated. [19] The 1,3-dipolar cycloadditions of diazomethane, nitrile oxide, and nitrone to C 60 were studied Keywords: cycloaddition · density functional calculations · Diels-Alder reactions · distortion/interaction theory · Marcus theory · ONIOM Abstract: Diels-Alder cycloadditions of butadiene and 1,3-dipolar cycloadditions of azomethine ylide, fulminic acid, and the parent nitrone to polyacenes, fullerenes, and nanotubes have been investigated with density functional theory and ONIOM methods.…”

Efficient Synthesis of C2v‐Symmetrical Pentakisadducts of C60 as Versatile Building Blocks for Fullerene Architectures that Involve a Mixed Octahedral Addition Pattern

“…[15] To investigate the potential of isoxazolines to serve as a protective group in the synthesis of fullerene pentakisadducts, we targeted the synthesis of mixed [5:1]hexakisadduct 1 c (Scheme 1), which bears ten acid-labile tert-butyl-protected carboxylic groups. Fivefold cyclopropanation with bis[3-(tert-butoxycarbonyl)propyl] malonate [18] was achieved by using the modified reaction conditions for the synthesis of fullerene hexakisadducts [19,20] in 42 % yield.…”

“…[13,14] More recently, it was reported that isoxazolines can also be cleaved under less harsh conditions by heating to reflux in o-dichlorobenzene with an excess amount of a dienophile and Cu II catalysis. [15] We report now a much milder photolytic cleavage of a mixed [5:1]-fullereno isoxazoline adduct 1 prepared from the isoxazolinofullerene 2 [15][16][17] to yield directly C 2v -symmetrical pentakisadducts. The discovery opens now the door to very facile access to complex fullerene-based architectures that involve a mixed octahedral addition pattern.…”