Chemistry Reference
In-Depth Information
Cyclizations have also been studied in derivatives of bianthrone (3) and other
BAEs [
91
-
96
]. A doubly cyclized bianthrone derivative, hypericin (16), is a
prominent component in St John's wort (
Hypericum perforatum
, German
Johanneskraut), an important remedy for depression [
97
]. Hypericin also is an
antiretroviral agent with potential
anti
-AIDS capabilities [
98
]. Hypericin has no
fjord regions but is nevertheless non-planar and chiral due to the overcrowding in
the substituted bay regions. The barrier for enantiomerization is ~98 kJ/mol [
99
].
Compound 17, prepared by photocyclization of 14, has bona fide fjord regions on
both sides of a central naphthalene unit and a twisted conformation in the crystal
structure [
100
].
OH
O
OH
O
HO
CH
3
CH
3
HO
OH
O
OH
O
16
17
18
The hexabenzoperylene 18 features a red twisted conformer as well as a yellow
anti
-folded conformation [
101
]. The non-planarity of this benzenoid PAH is due to
overcrowded fjord regions that are, however, positioned on both sides of a central
benzene ring. The above examples indicate that similar conformational spaces and
dynamic stereochemistries as reviewed for BAEs in this Chapter may also be found
in large PAHs with double coves and/or fjords [
31
,
102
].
A threefold PAE has been realized in the star-shaped 5,10,15-tri(fluorenylidene)
truxene (19)[
103
], which is purple in solution and forms reddish crystals [
104
].
The three bifluorenylidene units share one central six-membered ring and the
