Chemistry Reference
In-Depth Information
2
1
3
sub-topics such as metal complexes and surface chemistry are not directly
addressed in this chapter.
2 Corannulene and Its Derivatives
The two key synthetic methods for preparing buckybowls can be classified as the
solution-phase protocol and flash vacuum pyrolysis (FVP). Both methods have their
advantages and limitations. The conventional solution-phase synthesis needs a
special synthesis strategy to accommodate the additional strain energy of the
bowl molecules; therefore, overcoming lengthy synthetic steps and low overall
yields have been long-standing challenges. High-temperature pyrolysis routes can
address some of the issues, but this strategy also suffers from several drawbacks:
(1) modest yields, (2) almost no functional group tolerance, (3) small scale runs,
and (4) the potential for thermal rearrangements of the molecule framework at high
temperatures (1,000-1,300
C) leading to undesired products [
16
]. Thus, the syn-
thesis of buckybowls under mild synthetic conditions (in solution phase) on a
kilogram scale became an important goal for facilitating the expansion of
corannulene-based research. Fortunately, various halogenated corannulenes are
accessible from corannulene, and metal-catalyzed/mediated reactions provide effi-
cient methods in mild conditions for carbon-carbon bond formation (or ring clo-
sure) and enrich buckybowl chemistry.
2.1 Corannulene and Simple Corannulene Derivatives
2.1.1 Pioneering Syntheses
Corannulene (1) was synthesized by Lawton and Barth in 1966 [
17
,
18
]. As
mentioned by them: “Within its structural framework is an unusual strain resulting
from the geometrical requirement that the bond angles deviate appreciably from the
normal values found for benzenoid compounds.” Thus, introduction of strain as late
as possible is key to their synthetic strategy for the preparation of 1 [
19
]. Their
synthesis started with acenaphthene, and after numerous synthetic steps the key
intermediate 4 was obtained (Scheme
1
). The diol acid 4 was converted to 5 upon
