Chemistry Reference
In-Depth Information
1
2
3
4
Scheme 3 Typical naphthalenophanes
3.1 Naphthalenophanes
[2.2]Naphthalenophanes (the chain length of each linker in brackets) have a cyclic
framework consisting of two naphthalene units and two ethylene linkers. There are
several possible structures depending on the bridging positions and the
conformations. For example, [2.2](2,6)naphthalenophane (the substituted positions
in parentheses) has two isomers 1 and 2 that differ in the direction of two 2,6-
naphthylene units (Scheme
3
)[
30
,
31
]. Chiral isomer 2 was resolved by the
formation of diastereomeric charge transfer complexes. Similarly, chiral and achi-
ral isomers of [2.2](1,5)naphthalenophane were separated [
32
]. The two aromatic
units are so closed that the molecules suffer from severe strains and have little
flexibility. Therefore these compounds are good models to examine transannular
interactions between naphthalene chromophores at various orientations. Analogous
[3.3]naphthalenophanes with two 1,3-propylene linkers are less strained and more
flexible than the corresponding [2.2]naphthalenophanes [
33
,
34
]. Two isomers of
[3.3](1,4)naphthalenophanes 3 and 4 underwent cycloaddition upon irradiation and
these photoproducts reverted to the original compounds upon heating.
3.2 Anthracenophanes
Two anthracene units are linked firmly by two ethylene linkers in [2.2](9,10)
anthracenophane 5, which was readily synthesized from 9,10-bis(chloromethyl)
anthracene (Scheme
4
)[
35
]. A photochemical reaction of this compound gave a
cyclization product via a biradical intermediate. Two isomers of [2.2](1,4)
anthracenophane, 6 and 7, were synthesized by Hofmann elimination [
36
,
37
].
Upon irradiation at 374 nm,
syn
isomer 7 readily gave [4+4]cycloaddition product
8 at the 9,10-positions and this photoproduct was reverted to 7 by heating or
irradiation at 254 nm. The UV spectra of the two isomers indicated that the
bathochromic shift due to transannular interactions was more significant in
syn
7
than
anti
6 because the two anthracene units were fully overlapped in the former.
