Chemistry Reference
In-Depth Information
Scheme 7 The 1,3-dipolar cycloaddition reaction of N-metalated azomethine ylide on
La@C
72
(C
6
H
3
Cl
2
) (as a racemic mixture), using Cu(II) Fesulphos complex as a catalyst, affords
eight different optically active pyrrolidines with a fixed (2
S
,5
S
) configuration
formed from the clockwise enantiomers exhibit circular dichroism (CD) spectra
that are opposite in sign to those derived from the anticlockwise enantiomer.
2.3 Retro-Cycloaddition Reactions of Fullerene Cycloadducts
Among the many well-known exohedral reactions developed on the fullerene
sphere, cycloaddition reactions have played a prominent role with applications in
fields such as medicinal chemistry [
49
] and materials science [
50
]. The fullerene
derivatives obtained through this functionalization method display, in general, an
acceptable degree of stability; however, in the last few years a number of studies
have reported efficient retro-cycloaddition methodologies for the most important
fullerene cycloadducts. In this section we will describe the different retro-
cycloaddition conditions for each type of fullerene derivative, and the applications
of these methodologies to carry out protection-deprotection protocols that could
selectively add or
remove addends
from fullerenes while leaving others
unperturbed.
2.3.1 Retro-Diels-Alder Reaction
Fullerenes are excellent dienophiles that can undergo [4+2] cycloaddition reactions
with different dienes such as anthracene or cyclopentadiene. This reaction is
controlled by the properties of the dienes and can proceed at room temperature, at
reflux or under microwave irradiation. The rate of Diels-Alder reaction is affected
