Synthesis and Structure of Novel 1,8-Bridged Fluorenophanes

Article abstract of DOI:10.1039/a605440d

A novel 1,8-bridged fluorenophane (4a) is found to assume an 'inward-folded' conformation with the bulky tart-butyl group located in the cavity, a situation which is different from the conformation of the corresponding dithiafluorenophane (3a).

Full text of DOI:10.1039/a605440d

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1
68 J. CHEM. RESEARCH (S), 1997
J. Chem. Research (S),
Synthesis and Structure of Novel 1,8-Bridged
1
997, 168–169†
Fluorenophanes†
a
a
a
a
Akihiko Tsuge,* Yasuhiro Ueda, Tadashi Araki Tetsuji Moriguchi, Kazunori
a
b
b
b
Sakata, Keizo Koya, Shuntaro Mataka and Masashi Tashiro
a
Department of Chemistry, Kyushu Institute of Technology, Tobata-ku, Kitakyushu 804, Japan
b
Institute of Advance Material Study, Kyushu University, Kasuga, Fukuoka 816, Japan
A novel 1,8-bridged fluorenophane (4a) is found to assume an ‘inward-folded’ conformation with the bulky tert-butyl group
located in the cavity, a situation which is different from the conformation of the corresponding dithiafluorenophane
(3a).
R
Cyclophanes are cyclic compounds consisting of aromatic
units. Many aromatic components have been used in the
But
But
6
8
3
HSH2C
CH2SH
1
cyclophane skeleton. Considerable attention has been paid
+
to particular properties of the components, because of the
strained structure of the ring system and its ability to form
p-electronic interactions. It is of interest to examine the
properties of a fluorene unit in cyclophane compounds,
because of its aromatic nature and acidic proton. To the best
of our knowledge, however, [2.2](2,7)fluorenophane is the
1
ClH2C
CH2Cl
But
1
2a R = H
b R = Me
2c R = OMe
2
i
2
only example to have been investigated so far. This is due to
But
But
difficulties in introducing a functional group into sites other
than the 2- and 7-positions by electrophilic reactions. In pre-
5
6
3
vious work we found that a chloromethyl group can be intro-
duced into the 1,8-positions of the fluorene molecule by
treatment with chloromethyl methyl ether in the presence of
an appropriate Lewis acid. This chloromethylated fluorene
should be a precursor for the synthesis of fluorenophane
compounds. Thus, we describe here the synthesis of novel
9
2
11
R
ii
S
R
S
1
,8-bridged fluorenophanes and their conformational
16
18
13
15
But
properties.
But
But
But
Treatment of 3,6-di-tert-butylated fluorenophane with
4
a R = H
4b R = Me
4c R = OMe
3a R = H
3b R = Me
3c R = OMe
chloromethyl methyl ether in the presence of TiCl gave the
4
1
,8-bis(chloromethyl)fluorene 1 in 58% yield. Bromination
But
Me
But
Me
of 4-tert-butyl-m-xylene with N-bromosuccinimide (NBS),
followed by treatment with thiourea afforded the bis(thiol)
2
a. Compounds 2b and 2c were obtained according to
4
reported methods. Cyclization of 1 and 2a–c using CsOH as
a base under highly dilute conditions afforded the corre-
sponding dithiafluorenophanes (3a–c) in 72–84% yields
5
(
Scheme 1).
Scheme 1 Reagents and conditions: i, CsOH, EtOH;; ii,
1
The H NMR spectra of 3a–c are summarized in Table 1.
MCPBA, then 500 °C, 2 Torr
Signals for the CH bridge reflect the dynamic behaviour of
2
the dithiafluorenophane. The C-9 hydrogens of 3a show a
broad singlet, indicating that inversion of the ring at room
temperature is slow on the NMR time-scale. In contrast, a
pair of doublets with a separation of 22 Hz was observed in
the spectra of 3b and 3c. These results strongly suggest that
the barrier to inversion in dithiafluorenophanes depends on
the bulkiness of the inner substituent (R).
ring being folded into the cavity produced by the other two
5
aromatic rings.
Taking into account these results and the chemical shifts of
the tert-butyl protons, it may be deduced that the dithia-
fluorenophanes 3a–c assume a conformation in which the
substituent R of the benzene ring is accommodated inside the
cavity. After oxidation of 3a–c with m-chloroperbenzoic acid
(MCPBA), pyrolysis was carried out in order to obtain the
fluorenophanes 4a–c (Scheme 1). However, in spite of
repeated trials, all attempts to prepare 4b and 4c resulted in
failure, in most cases only the dimethyl compound 5 being
isolated from very complex mixtures. In contrast, in the case
of 3a the desired fluorenophane 4a was obtained in 29%
yield. This is certainly due to steric hindrance of the sub-
stituent R during recombination of radical intermediates in
pyrolysis: even when hydrogen was the substituent, the yield
was not good.
In order to determine for 3a the coalescence temperature
and the free energy of activation for inversion, the tempera-
1
ture-dependent H NMR technique was employed. The mea-
sured barrier for the observed dynamic process is 11.54 kcal
ꢀ
1
mol at ꢀ15 °C in CDCl .‡
3
In contrast, there were no changes in the NMR signals for
b or 3c, even at 150 °C in [ H ]Me SO, indicating that 3b and
c have rigid structures.
We have already prepared various metacyclophanes con-
2
3
3
6
2
sisting of three aromatic rings and confirmed their ‘inward-
folded’ conformation, which is characterized by one aromatic
1
Data for the H NMR spectrum of 4a are also shown in
Table 1. In 4a it is noted that the protons of the tert-butyl
group attached to the benzene ring show an unexpectedly
upfield shift, suggesting a conformation in which the tert-
butyl group is located in the cavity formed by the p-cloud of
the fluorene ring. This is in fairly good agreement with a
considerable upfield shift of the aromatic protons adjacent to
*
To receive any correspondence (e-mail: tsuge@che.kyutech.ac.jp).
This is a Short Paper as defined in the Instructions for Authors,
†
Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
‡
1 cal = 4.184 J.

View Article Online
J. CHEM. RESEARCH (S), 1997 169
1
Table 1 H NMR spectra of fluorenophanes [d values (CDCl
3
)]
Dithiafluorenophanes 3. General Procedure: Preparation of
6
,15,18-tri-tert-butyl-2,11-dithia[3]metacyclo[3](1,8)fluorenophane
t
3
Compound
Bu
R
9-H
3a.sA solution of 1 (1.09 g, 2.9 mmol) and 2a (0.70 g, 3.1 mmol)
in EtOH–benzene (1:1; 300 ml) was added dropwise from a Hersh-
berg funnel with stirring to a solution of CsOH (1.21 g, 8.07 mmol)
1
1.41 (18 H)
1.33 (9 H)
3.95 (s)
and NaBH
had been evaporated, the residue was extracted with CH
extract was washed with water, dried over MgSO , and evaporated
in vacuo to give 3a (1.22 g, 79%) as colourless prisms, mp
34–235 °C (from hexane) (Found: C, 79.32; H, 8.41. C35
4
(0.12 g, 3.2 mmol) in EtOH (2 l) for 1 h. After solvents
3
3
3
4
a
b
c
7.09
2.69 (br s)
2
Cl . The
2
1
.37 (18 H)
1.32 (9 H)
.36 (18 H)
1.32 (9 H)
.36 (18 H)
(Ar-H)
4
2.39
(CH )
3
1.89 (d, J 22 Hz)
2.90 (d, J 22 Hz)
1
2
H
44 2
S
ǹ
requires C, 79.47; H, 8.40%); m/z 528 (M ); d
18 H, s), 2.70 (2 H, br s), 3.70 (4 H, s), 3.74 (4 H, s), 7.17 (2 H, d,
J 1.5 Hz), 7.19 (2 H, s), 7.45 (1 H, s), 7.62 (2 H, d, J 1.5 Hz).
,15,18-Tri-tert-butyl-2,11-dithia[3]metacyclo[3](1,8)fluoreno-
phane 3b.s3b was obtained according to the general procedure.
H
1.34 (9 H, s), 1.38
3.86
(OCH
2.03 (d, J 22 Hz)
3.20 (d, J 22 Hz)
(
1
3
)
a
0.69 (9 H)
7.09
(Ar-H)
3.07 (d, J 19 Hz)
3.80 (d, J 19 Hz)
6
1.37 (18 H)
3
4
Thus 1 (0.53 g, 1.41 mmol) and 2b (0.35 g, 1.46 mmol) gave 3b
(
0.64 g, 84%) as colourless prisms, mp 189–191 °C (from hexane)
S
But
(Found: C, 79.83; H, 8.49. C H S requires C, 79.63; H, 8.56%);
36 46
2
H
ǹ
But
m/z 542 (M ); d
H
1.32 (9 H, s), 1.36 (18 H, s), 1.90 (1 H, d, J 22 Hz),
2
.39 (3 H, s), 2.90 (1 H, d, J 22 Hz), 3.48 (2 H, d, J 12 Hz), 3.74 (2 H,
d, J 14 Hz), 3.95 (2 H, d, J 14 Hz), 3.99 (2 H, d, J 12 Hz), 7.14 (2 H,
s), 7.15 (2 H, d, J 1.5 Hz), 7.61 (2 H, d, J 1.5 Hz).
S
But
6
,15,18-Tri-tert-butyl-9-methoxy-2,11-dithia[3]metacyclo[3]-
(
1,8)fluorenophane 3c.s3c was obtained according to the general
3a
3
4
procedure. Thus 1 (0.32 g, 0.85 mmol) and 2c (0.23 g, 0.90 mmol)
gave 3c (0.34 g, 72%) as colourless prisms, mp 191–193 °C (from
hexane) (Found: C, 77.58; H, 8.50. C36
.31%); m/z 558 (M ); d
H
46
S
2
O requires C, 77.35; H,
1.32 (9 H, s), 1.35 (18 H, s), 2.03 (1 H, d,
ǹ
But
8
H
But
H
J 22 Hz), 3.21 (1 H, d, J 22 Hz), 3.51 (2 H, d, J 12 Hz), 3.60 (2 H, d,
J 14 Hz), 3.86 (3 H, s), 3.93 (2 H, d, J 14 Hz), 3.99 (2 H, d, J 12 Hz),
7
.13 (2 H, d, J 1.5 Hz), 7.18 (2 H, s), 7.58 (2 H, d, J 1.5 Hz).
5
,13,16-Tri-tert-butyl[2]metacyclo[2](1,8)fluorenophane 4a.—The
δ 5.84
But
sulfone derivative of 3a (0.52 g, 0.88 mmol) was pyrolysed at 500 °C
under reduced pressure (2 Torr) in a horizontal quartz tube. The
resultant product was chromatographed with hexane as an eluent
to afford 4a (0.12 g, 29%) from the first fraction as colourless
4a
Scheme 2
needles, mp 296–298 °C (from hexane) (Found: C, 90.16; H, 9.66.
ǹ
C
1
35
H
44 requires C, 90.44; H, 9.54%); m/z 464 (M ); d
H
0.69 (9 H, s),
the tert-butyl group. Inversion of one aromatic ring occurs
.37 (18 H, s), 2.93–3.86 (8 H, m), 3.07 (1 H, d, J 19 Hz), 3.80 (1 H,
d, J 19 Hz), 5.83 (2 H, s), 6.91 (2 H, d, J 1.5 Hz), 7.09 (1 H, s), 7.23
(2 H, d, J 1.5 Hz).
during the transformation into a smaller cyclic system
(
Scheme 2).
Further investigations of other types of 1,8-bridged fluor-
enophanes are in progress.
Received, 5th August 1996; Accepted, 21st January 1997
Paper E/6/05440D
Experimental
1
All melting points are uncorrected. H NMR spectra were
recorded at 500 MHz on a Nippon Denshi JEOL a-500 spectro-
meter in CDCl
3
with Me Si as an internal reference. Mass spectra
4
References
were obtained on a Nippon Denshi JEOL DX-300 spectrometer at
7
5 eV using a direct-inlet system. Elemental analyses were carried
1 F. V o¨ gtle, Supramolecular Chemistry, Wiley, Chichester, 1989; F.
Diederich, Cyclophanes, The Royal Society of Chemistry, Cam-
bridge, 1991; F. V o¨ gtle, Cyclophane Chemistry, Wiley, Chichester,
1989.
out on a Yanaco MT-3 spectrometer. Column chromatography was
performed on silica gel (Wako gel, C-300).
(
3-tert-Butyl-5-sulfanylmethylphenyl)methanethiol 2a.sA solu-
tion of 1,3-bis(bromomethyl)-5-tert-butylbenzene (30 g, 93 mmol)
and thiourea (18.0 g, 0.24 mol) in DMSO (450 ml) was stirred at
room tempearture for 15 h under an argon stream. After the reac-
tion mixture had been poured into cold 10% aqueous NaOH (500
ml) and acidified with 10% hydrochloric acid, it was extracted with
2 M. W. Haenel, Tetrahedron Lett., 1976, 3121; 1977, 1273.
3 A. Tsuge, T. Yamasaki, T. Moriguchi, T. Matsuda, Y. Nagano, H.
Nago, S. Mataka, S. Kajigaeshi and M. Tashiro, Synthesis, 1993,
205.
4 M. Tashiro and T. Yamato, J. Org. Chem., 1981, 46, 1543.
5 A. Tsuge, T. Sawada, S. Mataka, N. Nishiyama, H. Sakashita and
M. Tashiro, J. Chem. Soc., Chem. Commun., 1990, 1066; A. Tsuge,
T. Sawada, S. Mataka, N. Nishiyama, H. Sakashita and M. Tashiro,
J. Chem. Soc., Perkin Trans 1, 1992, 1489; A. Tsuge, H. Takeo, H.
Kabashima, T. Moriguchi, S. Mataka and M. Tashiro, Chem. Lett.,
1996, 425.
CH
2
Cl
2
. The extract was washed with water, dried over MgSO , and
4
evaporated in vacuo to leave a residue which was distilled to afford
the bis(thiol) 2a (16.5 g, 79%) as a colourless liquid, bp 140–145 °C
at 2 Torr (Found: C, 63.86; H, 8.13. C12
H
18
S
2
requires C, 63.65; H,
1.31 (9 H, s), 1.75 (2 H, t, J 8 Hz), 3.70
4 H, d, J 8 Hz), 7.12 (1 H, s), 7.19 (2 H, s).
ǹ
8
.03%); m/z 226 (M ); d
H
(