Chemistry Reference
In-Depth Information
Fig. 27 Representative examples of cycloaddition monoadducts obtained by chemical reaction
with Sc
3
N-
I
h
@C
80
([6,6]-junctions) and those between pentagonal and hexagonal rings ([5,6]-
junctions) [
200
]. Several reactions have already been reported considering these
C
80
cages: carbene additions [
201
], radical trifluoromethylations [
202
], or free
radical additions [
203
], even though cycloaddition reactions are the most effective
way to generate covalent derivatives of endohedral metallofullerenes to date.
[4+2]Cycloadditions.
The Diels-Alder monoadduct resulting from heating an
excess of 6,7-dimethoxyisochroman-3-one and Sc
3
N@C
80
in trichlorobenzene
(Fig.
27
) was the first isolated organic derivative of a TNT endofullerene [
204
].
NMR experiments served to identify the regioisomer obtained as the one localized
in a [5,6] ring junction of the
I
h
isomer, which was later corroborated by solving the
X-ray structure of the Diels-Alder monoadduct [
205
]. TNT endofullerenes have
a much lower reactivity than empty fullerenes and classical endohedral
metallofullerenes and Dorn and co-workers used this selective reactivity to purify
TNT endohedral metallofullerenes directly from as-prepared soots in a single facile
step in Diels-Alder reactions with a cyclopentadiene-functionalized resin [
206
].
[3+2]Cycloadditions.
So far these have been the processes more intensively
investigated, in particular 1,3-dipolar cycloaddition reactions of azomethyne ylides
to yield fulleropyrrolidines (Fig.
27
)[
200
,
207
], disilirane additions [
208
], and
more recently cycloadditions with epoxides such as tetracyanoethylene oxide [
209
],
or azides to form azafulleroids after nitrogen extrusion [
210
].
