Synthesis and properties of [2.2]paracyclo- and [2.2](1,4)naphthaleno-(3,6)carbazolophanes

Article abstract of DOI:10.1246/cl.2002.934

[2.2]Paracyclo(3,6)carbazolophane (1a) and [2.2](1,4)-naphthaleno(3,6)carbazolophane (1b) were prepared. The structures of 1a and 1b were characterized by ¹H NMR. X-ray analysis of 1a revealed that the carbazole ring extremely deviates from the

Full text of DOI:10.1246/cl.2002.934

934
Chemistry Letters 2002
Synthesis and Properties of [2.2]Paracyclo- and [2.2](1,4)Naphthaleno-(3,6)carbazolophanes
Keita Tani,ꢀ Koh Matsumura, Kazushige Hori, Yasuo Tohda, Hiroyuki Takemura,y Hideo Ohkita,yy
Shinzaburo Ito,yy and Masahide Yamamotoyy
Division of Natural Science, Osaka Kyoiku University, Asahigaoka, Kashiwara, Osaka 582-8582
y
Department of Chemistry, Faculty of Science, Kyushu University, Ropponmatsu 4-2-1, Chuo-ku, Fukuoka 810-8560
yyDepartment of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501
(Received June 11, 2002; CL-020494)
[2.2]Paracyclo(3,6)carbazolophane (1a) and [2.2](1,4)-
afforded the desired 1a6 in 59% yield. Similar reaction sequence
was applied for 1,4-bis(bromomethyl)naphthalene 4b in place of
4a to give 1b7 in 21% overall yield. Both 1a and 1b were noted to
be the first example of carbazolophanes not only bridged by short
[2.2]-phane framework, but also belonging to the mixed-
carbazolophanes, where the carbazole and other aromatic
chromophores were fixed in a distinct geometry.
naphthaleno(3,6)carbazolophane (1b) were prepared. The struc-
tures of 1a and 1b were characterized by 1H NMR. X-ray analysis
of 1a revealed that the carbazole ring extremely deviates from the
conjugated plane. Electronic spectra of 1a and 1b showed the
broadening and bathochromic shift compared with the references.
It is well known that the poly(N-vinylcarbazole) is a famous
photoconductive aromatic polymer and the photophysical proper-
ties of carbazole chromophores have attracted much attention.1
We have recently reported the synthesis and photophysical
properties of [m.n]carbazolophane derivatives to elucidate the
interchromophoric interaction in carbazole moiety.2 Cyclophane
has been employed as useful model compounds for examining
weak transannular interaction in aromatic systems and for
studying the novel structure of the strained aromatic rings.3
However, neither the transannular ꢀ–ꢀ electronic interaction
between carbazole and other aromatic ring nor the properties of
the strained carbazole ring have been sufficiently studied so far.
Thus, we describe here the synthesis, spectral and structural
properties of [2.2]paracyclo(3,6)carbazolophane (1a) and
[2.2](1,4)naphthaleno(3,6)carbazolophane (1b).
Scheme 1.
The structures of the carbazolophanes were primarily
characterized by 1H NMR spectroscopy. The chemical shifts of
aromatic rings of 1a, 1b, and the references, 9-ethyl-3,6-
dimethylcarbazole 6, p-xylene 7, and 1,4-dimethylnaphthalene
8 are summarized in Table 1. The carbazole protons in 1a and 1b
appeared at distinguishable ABX system. These signals shifted
generally at higher field compared with those of 6 owing to the
anisotropic effect of a faced aromatic ring. Marked high-field
shifts were observed for H4 and Ha, both of which are located
nearly above the opposed aromatic ring. On the other hand, a
slight low-field shift was observed for Hb of 1a and 1b, Hc of 1b
compared with the corresponding references. These protons are
situated apart from the center of the carbazole ring and hence, it is
assumed that they are in the deshielding field of the carbazole
benzene rings.
We have synthesized various [2n]cyclophanes by photo-
deselenation of selenacyclophanes,4 and this method was also
applied to the synthesis of 1a and 1b. Scheme 1 illustrates the
synthetic route of the carbazolophanes. Dibromide 22a was treated
with potassium selenocyanate to give 3,6-bis(selenocyanato-
methyl)-9-ethylcarbazole (3)5 in 90% yield. 1,4-Bis(bromo-
Table 1. Chemical shifts of aromatic rings (400 MHz, CDCl3, ꢁ)
methyl)benzene (4a) and
3 were coupled with sodium
H1H2
7.14
H4
7.00
Ha
6.74
Hb
4.75
Hc
7.16
borohydride under high dilution conditions to afford 5a in 56%
yield. Selenocyanate 3 was a stable solid and easily purified by
recrystallization in contrast to the unstability of bromide 2. As
selenacyclophanes are generally prepared from bromides and
selenocyanates, it is expected that various kinds of selena-
carbazolophanes will be prepared from 3 as key intermediates.
Photodeselenation of 5a with hexamethylphosphorous triamide
1a
Áꢁ À0.12 À0.26 À1.12 À2.31 þ0.10
1b 7.15 7.04 6.22 5.20 8.20
7.65
Áꢁ À0.11 À0.22 À1.64 À2.01 þ0.19 þ0.12
6
7
8
7.23–7.28
7.86
7.06 7.06
7.218.017.53
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
935
The structure of 1a was confirmed by the X-ray crystal
analysis as shown in Figure 1.8 The intramolecular distances
between bridged aromatic carbons, C4–C15 and C10–C18, are
Electronic absorption spectra of carbazolophanes and the
references were measured in THF. The absorption spectra of 1a
around 300 to 380 nm exhibited broadening and bathochromic
shift compared with 6 suggesting the existence of transannular ꢀ–
ꢀ electronic interaction. Similar trend was observed for 1b,
though the extent of broadening and bathochromic shift were
slightly larger than those for 1a. These results can be interpreted
by means of the exciton coupling interaction9 and the strain of the
carbazole chromophore which was revealed by the X-ray
analysis.
ꢀ
ꢀ
2.99 A and 2.97 A, respectively. The angle between right (C1–
C6) and left (C7–C12) side benzene in carbazole ring is as much
as 40 ꢁ as shown in Figure 1, while the upper benzene ring kept the
planarity. To our knowledge, this angle is the largest of all the
carbazole derivatives ever reported. Reflecting strong deforma-
ꢀ
tion from the conjugated plane, the distanceof C16–C3(3.22 A) is
ꢀ
shorter than that of C16–C2 (3.48 A). X-ray analysis of 1a
corresponded to the behavior of the chemical shifts of aromatic
protons in solution. Therefore, 1a remained the rigid structure
even in solution. From the comparison of the chemical shift
differences (Áꢁ) of 1a and 1b from the corresponding references
as shown in Table 1, 1b will be also rigid and the geometry of the
carbazole and the naphthalene is taken to be of anti-conformation.
In summary, both [2.2]paracyclo(3,6)carbazolophane 1a and
[2.2](1,4)naphthaleno(3,6)carbazolophane 1b were first prepared
by the photodeselenation of 5a and 5b, respectively. Their
chemical and physical properties were invetigated.10 It was also
found that the carbazole ring in 1a is able to endure the strong
deformation in the rigid [2.2]cyclophane framework.
References and Notes
1J. M. Pearson and M. Stolka, ‘‘Poly( N-vinylcarbazole),’’
Gordon and Breach Sci. Pub., New York (1981).
2
a) K. Tani, Y. Tohda, K. Hisada, and M. Yamamoto, Chem.
Lett., 1996, 145. b) Y. Nakamura, M. Kaneko, N. Yamanaka,
K. Tani, and J. Nishimura, Tetrahedron Lett., 40, 4693 (1999).
c) K. Tani, Y. Tohda, H. Takemura, H. Ohkita, S. Ito, and M.
Yamamoto, J. Chem. Soc., Chem. Commun., 2001, 1914. d)
H. Ohkita, S. Ito, M. Yamamoto, Y. Tohda, and K. Tani, J.
Phys. Chem. A, 106, 2140 (2002).
3
4
5
For example: P. M. Keehn and S. M. Rosenfeld, ‘‘Cyclo-
phanes,’’ Academic Press, New York (1983); F. Vogtle,
¨
‘‘Cyclophane Chemistry,’’ Wiley, Chichester (1989); F.
Diederich, ‘‘Cyclophanes,’’ The Royal Society of Chemistry,
Cambridge (1991).
a) K. Tani, H. Seo, M. Maeda, K. Imagawa, N. Nishiwaki, M.
Ariga, Y. Tohda, H. Higuchi, and K. Kuma, Tetrahedron
Lett., 36, 1883 (1995). b) H. Higuchi, K. Tani, T. Otsubo, Y.
Sakata, and S. Misumi, Bull. Chem. Soc. Jpn., 60, 4027
(1987).
3: dec. 139–141 ꢁC, 1H NMR (CDCl3, ꢁ): 1.44 (t, J ¼ 7:2 Hz,
3H), 4.36 (q, J ¼ 7:2 Hz, 2H), 4.59 (s, 4H), 7.40 (d,
J ¼ 8:4 Hz, 2H, H1), 7.49 (dd, J ¼ 8:4 Hz, 1.6 Hz, 2H, H2),
8.08 (d, J ¼ 1:6 Hz, 2H, H4). Anal. Calcd for C18H15N3Se2:
C, 50.13; H, 3.51; N, 9.74%. Found: C, 49.85; H, 3.43; N,
9.49%.
Figure 1. X-ray analysis of 1a.
6
7
8
1a: mp 164–165 ꢁC: Anal. Calcd for C24H23N: C, 88.57; H,
7.12; N, 4.30%. Found : C, 88.29; H, 7.07; N, 4.29%.
1b: mp 197–199 ꢁC: Anal. Calcd for C28H25N: C, 89.56; H,
6.71; N, 3.73%. Found : C, 89.40; H, 6.69; N, 3.58%.
Crystal Data for 1a: colorless prism (benzene-hexane),
Mr ¼ 325:45, monoclinic, space group P21/c, a ¼
ꢀ
ꢀ
ꢀ
5:722ð2Þ A, b ¼ 17:471ð2Þ A, c ¼ 18:109ð2Þ A, ꢂ ¼
ꢀ 3
ꢁ
94:92ð2Þ , V ¼ 1803:7ð8Þ A , Z ¼ 4, Dcalc ¼ 1:198 g/cm3,
ꢃðMo KꢄÞ ¼ 0:69 cmÀ1, Rigaku AFC7R diffractometer,
1866 reflections with I > 3:0ꢅðIÞ, R ¼ 0:046, Rw ¼ 0:032.
M. Kasha, H. R. Rawls, and M. A. El-Bayoumi, Pure Appl.
Chem., 11, 371(1965).
9
10 The emission properties of 1a and 1b are of particular interest
and will be reported in a separated paper.
Figure 2. Electronic absorption spectra in THF.