The synthesis and property of dihydropyrene derivatives containing a nitrogen atom

Article abstract of DOI:10.1080/15421400701503667

Dihydropyrene (DHP) is 14π aromatic compound and applied as an aromatic probe by chemical shift of internal methyl groups in 1H-NMR spectra. DHP containing a nitrogen atom 1a and 2a were designed as photochromic compounds which were restrained thermal-isomerization. 1a and 2a were confirmed as DHP types by 1H-NMR spectra. Chemical shifts of internal methyl groups of 1a and 2a were observed at the lower magnetic field than that of DHP 3a. According to optimized structures of 1a and 3a, it was expected that the internal methyl group located of the out at center of 14π annulene ring. Isomerization to [2.2]metacyclophanediene 1b from DHP 1a by photo-irradiation of visible light was not observed.

Full text of DOI:10.1080/15421400701503667

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The Synthesis and Property
of Dihydropyrene Derivatives
Containing a Nitrogen Atom
a
a
Kazufumi Chifuku , Tsuyoshi Sawada , Yutaka
a
a
Kuwahara & Hideto Shosenji
a
Department of Science and Technology for
Chemistry and Physics, Graduate School of Science
and Technology, Kumamoto University, Kumamoto,
Japan
Published online: 22 Sep 2010.
To cite this article: Kazufumi Chifuku , Tsuyoshi Sawada , Yutaka Kuwahara & Hideto
Shosenji (2007) The Synthesis and Property of Dihydropyrene Derivatives Containing
a Nitrogen Atom, Molecular Crystals and Liquid Crystals, 470:1, 369-381, DOI:
10.1080/15421400701503667
To link to this article: http://dx.doi.org/10.1080/15421400701503667
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Mol. Cryst. Liq. Cryst., Vol. 470, pp. 369–381, 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701503667
The Synthesis and Property of Dihydropyrene
Derivatives Containing a Nitrogen Atom
Kazufumi Chifuku
Tsuyoshi Sawada
Yutaka Kuwahara
Hideto Shosenji
Department of Science and Technology for Chemistry and Physics,
Graduate School of Science and Technology, Kumamoto University,
Kumamoto, Japan
Dihydropyrene (DHP) is 14p aromatic compound and applied as an aromatic
1
probe by chemical shift of internal methyl groups in H-NMR spectra. DHP con-
taining a nitrogen atom 1a and 2a were designed as photochromic compounds
which were restrained thermal-isomerization.
1
1
a and 2a were confirmed as DHP types by H-NMR spectra. Chemical shifts of
internal methyl groups of 1a and 2a were observed at the lower magnetic field
than that of DHP 3a. According to optimized structures of 1a and 3a, it was
expected that the internal methyl group located of the out at center of 14p annulene
ring.
Isomerization to [2.2]metacyclophanediene 1b from DHP 1a by photo-irradiation
of visible light was not observed.
Keywords: aromaticity; dihydropyrene; [2.2]metacyclophanediene; photochromism;
photo switching device
INTRODUCTION
Dihydropyrene (DHP) derivatives are 14p aromatic compounds and
photo-, thermochromic compounds to [2.2]metacyclophanediene (MCPD)
We thank the Department of Science and Technology and Physics, Graduate School
of Science and Technology, Kumamoto University for support of this work.
Address correspondence to Tsuyoshi Sawada, Department of Science and Technology
for Chemistry and Physics, Graduate School of Science and Technology, Kumamoto
University, 2-39-1 Kurokami Kumamoto-Shi, Kumamoto 860-8555, Japan. E-mail:
sawada@kumamoto-u.ac.jp
369

3
70
K. Chifuku et al.
FIGURE 1 Isomerization of DHP and MCPD structures.
structure from DHP structure (Fig. 1)[1]. Therefore, trans-10b,10c-
dimethyl-dihydropyrene derivatives are researched as a probe of
aromaticity [2,3] and are expected to be photo switching devices
[
4–7].
On the other hand, the research that the atoms at internal position
of DHP structure change to heteroatoms (nitrogen, oxygen etc.) from
carbon have been limited [8]. Boekelheide tried synthesis of DHP
derivative 4a, that was replaced with two nitrogen atoms at
1
0b,10c-positions, but only MCPD structure 4b was observed. The iso-
merization to DHP structure 4a from MCPD structure 4b was not
occurred by heating or photo-irradiation (Fig. 2) [9].
We are interesting in that behavior for photo- and thermochromism
and aromaticity of DHP derivatives containing heteroatoms at the
internal position. Then, we synthesize DHP derivative 1a (Scheme 1),
and study about photo- and thermochromism of 1a.
FIGURE 2 Isomerization of 4a and 4b.

Dihydropyrene Containing a Nitrogen Atom
371
SCHEME 1 Target compound.
EXPERIMENTAL
Synthesis [10]
Synthesis of 2,6-Bis(Bromomethyl)-4-tert-Butyl
Toluene (6)
To a suspension of zinc powder (2.0 g, 30 mmol) in dry tetrahydro-
furan (100 ml), a solution of 1,2-dibromoethane (6.0 g, 32 mmol) in
dry tetrahydrofuran (10 ml) was added dropwise. After the mixture
was refluxed 6 h under nitrogen, a solvent was evaporated in vacuo
to afford zinc dibromide.
Secondly, to suspension of 4-tert-butyl toluene 5 (22 g, 150 mmol)
and zinc dibromide and trioxane (11.3 g, 120 mol) in 30 wt% hydro-
ꢀ
bromic acid in acetic acid (100 ml) was stirred at 85 C for 4 d under
nitrogen and then poured onto ice (100 ml). The mixture was carried
out decantation with heat hexane (50 ml ꢁ 4) and the supernatent
liquid was evaporated in vacuo, leaving a residue, which was subjected
to column chromatographed on silica gel (Waco-gel C-200E,
7
5 ꢂ 150 mm, eluent; hexane) and recrystalization with hexane, to
ꢀ
afford 6 (33 g, 66%) as colorless needle: mp 120 ꢂ 121 C (lit. [11]
ꢀ
1
1
4
20 ꢂ 121 C); H-NMR (400 MHz, CDCl ) d 1.32 (s, 9H), 2.48 (s, 3H),
3
.50 (d, 4H), 7.26 (s, 2H).
Synthesis of 2,6-Bis(Mercaptomethyl)-4-tert-Butyl
Toluene (7)
A suspension of 6 (0.73 g, 2.2 mmol) and thoiurea (0.50 g, 6.6 mmol)
in ethanol (50 ml) was refluxed for 5 h under nitrogen. After the mix-
ture was cooled, an aqueous 10% potassium hydroxide solution

3
72
K. Chifuku et al.
(
10 ml) was added and refluxed for 3 h under nitrogen. Diluted hydro-
chloric acid was added slowly until the reaction solution become
slightly acidic and the mixture was extracted with chloroform. The
extract was dried over MgSO and evaporated in vacuo and recrysta-
4
lized with hexane, to afford 4 (0.26 g, 50%) as white powder: mp
ꢀ
ꢀ
1
9
9
6 ꢂ 97 C (lit. [2] 90 ꢂ 91 C); H-NMR (400 MHz, CDCl ) d 1.30 (s,
3
H), 1.68 (t, J ¼ 6.84 Hz, 2H), 2.48 (s, 3H), 4.50 (d, 4H), 7.26 (s, 2H).
Synthesis of Pyridine-2,6-Diethylester (9)
To ethanol (50 ml), thionyl chloride (1.7 ml. 22 mmol) was dropped
slowly with ice cooling under nitrogen. To it, a pyridine-2,6-dicar-
boxylic acid 8 (1.7 g, 10 mmol) was added and the mixture was refluxed
for 5 h under nitrogen. After the solvent was evaporated in vacuo. A
toluene (50 ml ꢁ 3) was added to the residue and evaporated in vacuo
3
times. The residue was extracted with diethyl ether (30 ml ꢁ 3). The
extract was washed with water, dried over MgSO and evaporated in
4
ꢀ
vacuo, to afford 9 (2.0 g, 90%) as colorless needle: mp 45 ꢂ 46 C (lit. [2]
ꢀ
ꢃ1
1
4
1 ꢂ 42 C); IR (KBr) 1710 cm ; H-NMR (400 MHz, CDCl ) d 1.46 (t,
3
J ¼ 7.32 Hz, 3H), 4.50 (q, J ¼ 7.32 Hz, 4H), 8.00 (t, J ¼ 7.81 Hz, 1H),
.29 (d, J ¼ 7.81 Hz, 2H).
8
Synthesis of Pyridine-2,6-Dimethylalcohol (10)
To the suspension of 9 (1.8 g, 8.0 mmol) in ethanol (20 ml), the sus-
pension of sodium borohydride (1.3 g, 35 mmol) in ethanol (20 ml) was
dropwise during a period of 1 h with ice cooling under mechanical stir-
ring. After the mixture was stirred at rt for 3 hour and was refluxed
for 5 h under nitrogen, solvent was evaporated in vacuo, and the satu-
rated aqueous solution of potassium carbonate was added to the resi-
ꢀ
due. After the mixture was stirred at 60 C for 2 h, the mixture was
extracted with chloroform (100 ml ꢁ 10). The extract was dried over
MgSO and evaporated in vacuo. to afford 10 (0.92 g, 83%). 10: white
4
ꢀ
ꢀ
1
powder: mp 113 ꢂ 115 C (lit. [2] 114 ꢂ 118 C); H-NMR (400 MHz,
CDCl ) d 3.49 (s, 2H), 4.60 (s, 4H), 7.20 (d, J ¼ 7.81 Hz, 2H), 7.72 (t,
3
J ¼ 7.82 Hz, 1H).
Synthesis of 2,6-Bis(Bromomethyl)Pyridine (11)
A solution of 10 (0.75 g, 5.4 mmol) in 30 wt% hydrobromic acid in
ꢀ
acetic acid (11 ml) was stirred at 100 C for 1.5 h and then poured onto
ice (20 ml) and neutralized with aqueous 1 M NaOH. The resulting
precipitate was collected and recrystallized with the mixture of hexane
and ethyl acetate, to afford 11 (1.0 g, 70%) as colorless needle: mp
ꢀ
ꢀ
1
8
(
5 ꢂ 87 C (lit. [3] 84 ꢂ 89 C); H-NMR (400 MHz, CDCl ) d 4.54
3
s, 4H), 7.38 (d, J ¼ 7.81 Hz, 2H), 7.71 (t, J ¼ 7.82 Hz, 1H).

Dihydropyrene Containing a Nitrogen Atom
373
Synthesis of Dithiametacyclophane (12)
To a solution of potassium hydroxide (0.34 g, 6.1 mmol) and sodium
borohydride (0.10 g, 2.6 mmol) in ethanol (1500 ml), a solution of 7
(
0.45 g, 1.9 mmol) and 11 (0.50 g, 1.9 mmol) in ethanol (500 ml) was
added dropwise over 24 h. After the solvent was evaporated in vacuo,
the residue was extracted with chloroform (30 ml ꢁ 3). The extract was
dried over MgSO and evaporated in vacuo, leaving a residue, which
4
was subjected to column chromatographed on silica gel (Waco-gel
C-200E, 75 ꢂ 150 mm, eluent; hexane=ethyl acetate, 5=1), to afford 12
ꢀ
ꢃ1
(
1
0.32 g, 50%) as white powder: mp 133 ꢂ 135 C; FT-IR 3021, 2954,
1
591, 1571, 1480, 1451, 1360, 1214, 1082 cm ; H-NMR (400 MHz,
CDCl ) d 1.33 (s, 9H), 2.56 (s, 3H), 3.61 (d, J ¼ 14.16 Hz, 2H), 3.76
3
(
d, J ¼ 15.63 Hz, 2H), 3.89 (d, J ¼ 15.13 Hz, 2H), 4.29 (d, J ¼ 15.13 Hz,
Hz, 2H), 6.86 (d, J ¼ 7.81 Hz, 2H), 6.90 (d, 2H), 7.23 (t, J ¼ 7.82 Hz,
þ
þ
1
H), MS (TOF) m=z 347 (M þ 4H); MS (FABþ) m=z 344 (M ꢃ 1H).
Anal. Calcd for C H S N: C, 69.92; H, 7.33; N, 4.08. Found: C,
2
0
25 2
6
9.47; H, 7.40; N, 3.94.
Synthesis of [2.2]Metacyclophane SMe Derivative (13)
To stirred solution of 12 (1.0 g, 2.9 mmol) in dry tetrahydrofuran
(
(
20 ml), 6.0 ml of a hexane solution (1.58 mol=l) of n-butyllithium
15 mmol) was added with ice cooling under nitrogen. After the mix-
ture was stirred for 3 h at rt, methyl iodide (1.0 ml, 15 mmol) was
added to the reaction mixture. After the mixture was stirred for
3
0 min, it was worked up by addition of H O and dichloromethane.
2
The extract was dried over MgSO and evaporated in vacuo. The resi-
4
due recrystallized with hexane, to afford 13 (0.82 g, 76%) as brown
ꢀ
powder; mp 116 ꢂ 118 C; FT-IR 2956, 2928, 2866, 1698, 1580, 1480,
ꢃ1;
1
1
0
3
441, 1361, 1230, 1202, 1039 cm
H-NMR (400 MHz, CDCl ) d
3
.57 (s, 3H), 1.37 (s, 9H), 2.11 (s, 6H), 2.77 (t, J ¼ 12.60 Hz, 2H),
.20 (dd, J ¼ 4.00 Hz, J ¼ 11.72 Hz, 2H), 3.38 (dd, J ¼ 4.00 Hz,
J ¼ 12.60 Hz, 2H), 7.15 (s, 2H), 7.64 (t, J ¼ 7.82 Hz, 1H), 7.81 (d,
J ¼ 7.81 Hz, 2H); MS (FAB) m=z 375 (Mþ þ 1H).
Preparation of Bis(Sulfonium) Salt (15)
To a solution of Trimethyl orthoformate (1.4 ml, 12 mmol) in dry
dichloromethane (5 ml), Boron trifluoride diethylether complex
ꢀ
(
2.1 ml, 16 mmol) was added at ꢃ30 C under nitrogen. After the mix-
ꢀ
ture was stirred at 0 C for 15 min, the solvent was decanted at
ꢀ
ꢃ30 C. The dry dichloromethane (5 ml) was added to the reaction mix-
ꢀ
ture and stirred at 0 C. Similarly, the decantation was performed 3
times, to afford dimethoxycarbonium tetrafluoroborate 14 as white
liquid in the reactor.

3
74
K. Chifuku et al.
Secondly, To dimethoxycarbonium tetrafluoroborate 14 in dichloro-
methane, a solution of 13 (0.92 g, 2.5 mmol) in dry dichloromethane
ꢀ
(
10 ml) was added at ꢃ30 C under nitrogen. The mixture was allowed
to warm to rt and was stirred for 4 h. Then ethyl acetate (50 ml) was
added, the mixture was stirred for 1 h, and the solvent was decanted.
Fresh ethyl acetate (50 ml) was added to the only residue and the sol-
ution was stirred for 3 h more. After the solvent was decanted more,
the resulting sticky residue was collected and dried in vacuo, to afford
ꢀ
1
5 (1.3 g, 90%) as brown powder: 139 ꢂ 141 C; FT-IR 3031, 2957,
ꢃ1
1
724, 1602, 1431, 1363, 1286, 1031 cm
.
Hofmann Elimination of 15 to Give (2a)
A suspension of 15 (100 mg, 0.17 mmol) and potassium tert-butox-
ide (100 mg, 0.9 mmol) in dry tetrahydrofuran (50 ml) was stirred at
rt overnight under nitrogen. The mixture was washed with aqueous
1
0% potassium hydroxide solution (50 ml ꢁ 3), water phase was
extracted with hexane (50 ml ꢁ 3). The extract was dried over MgSO
4
and evaporated in vacuo, leaving a residue, which was subjected to
column chromatographed on silica gel absorbed 3 wt% aqueous 25%
NH3 (Silica Gel 60, 70 ꢂ 230 mesh, eluent; hexane=ethyl acetate,
ꢀ
2
0=1), to afford 2a (1.5 mg, 3%) as dark purple powder: 83 ꢂ 85 C;
FT-IR 3037, 2962, 2913, 2868, 1577, 1535, 1437, 1389, 1260, 1091,
ꢃ1;
1
1
020, 862, 798 cm
H-NMR (400 MHz, C D ); d ꢃ2.55 (s, 3H),
6
6
1
.57 (s, 9H), 2.34 (s, 3H), 7.47 (d, J ¼ 7.82 Hz, 1H), 7.80 (t,
J ¼ 7.81 Hz, 1H), 7.93 (d, J ¼ 1.21 Hz, J ¼ 7.81 Hz, 1H), 8.22 (s, 1H),
8
.28 (s, 1H), 8.43 (d, J ¼ 7.82 Hz, 1H), 8.96 (s, 1H), 9.59 (dd,
þ
J ¼ 1.22 Hz, J ¼ 7.81 Hz, 1H); MS (TOF): m=z 322 (M þ 1H), 308
þ
þ
þ
(
2
M ꢃ 1CH þ 2H), 293 (M ꢃ 2CH þ 1H), 276 (M ꢃ 1SCH þ 1H),
3
3
3
þ
þ
62 (M ꢃ 1SCH ꢃ CH þ 1H); MS (FAB): m=z 322 (M þ 1H). Anal.
3
3
Calcd for C H NS: C, 78.46; H, 7.21; N, 4.36. Found: C, 78.01; H,
2
1
23
7
.33; N, 4.30.
Hofmann Elimination of 15 to Give (1a)
A suspension of 15 (100 mg, 0.17 mmol) and sodium hydride (81 mg,
3
.4 mmol) in dry tetrahydrofuran (50 ml) was refluxed 13 h under
nitrogen. The mixture was washed with aqueous 10% potassium
hydroxide solution (50 ml ꢁ 3), water phase was extracted with hexane
(
50 ml ꢁ 3), The extract was dried over MgSO and evaporated in
4
vacuo, leaving a residue, which was subjected to column chromato-
graphed on silica gel absorbed 3 wt% aqueous 25% NH (Silica Gel
3
6
0, 70 ꢂ 230 mesh, eluent; hexane=ethyl acetate, 20=1), to afford 1a
ꢀ
(
3.9 mg, 8%) as dark purple powder: 113 ꢂ 114 C; FT-IR 3037, 2958,
ꢃ1; 1
2
909, 2864, 1527, 1391, 1229, 1141, 1070, 985, 797 cm
H-NMR

Dihydropyrene Containing a Nitrogen Atom
375
(
7
400 MHz, C D ) d ꢃ2.62 (s, 3H), 1.62 (s, 9H), 7.54 (d, J ¼ 7.82 Hz, 2H),
6
6
.70 (t, J ¼ 7.81 Hz, 1H), 8.04 (d, J ¼ 7.81 Hz, 2H), 8.34 (s, 2H), 8.56 (d,
þ
J ¼ 8.30 Hz, 2H); MS (FAB): m=z 277 (M þ 1H). Anal. Calcd for
(
7
C H N þ 1=4H O): C, 85.82; H, 7.74; N, 5.00. Found: C, 85.79; H,
2
0
21
2
ꢃ1
ꢃ1
.84; N, 5.09. k
; 355 nm (e 25887 l mol
cm ), 530 nm (e
cyclohexane
ꢃ1
ꢃ1
ꢃ1
ꢃ1
4
537 l mol cm ), 718 nm (e 2007 l mol cm ).
Measurements
1
H-NMR spectra were recorded on a JOEL JNM-EX400 spectrometer
ꢀ
at 25 C. IR spectra were recorded as a KBr disk on a Shimazu JR-408.
FT-IR spectra were recorded on a Perkin-Elmer Instruments Spec-
trum One FT-IR Spectrometer. UV-Vis spectra were recorded on a
HITACHI U-3210 spectrometer. TOF mass spectral analyses were per-
TM
formed on a PerSeptive Biosystems Voyager RP. FAB mass spectral
analyses were performed on a JOEL JMS-DX303HF.
RESULTS AND DISCUSSION
Syntheses of starting materials 7 and 11 are shown in Scheme 2.
Compound 7 was yielded from 5 by two steps, and compound 11 was
obtained from 8 by three steps.
Syntheses of 1a and 2a are shown in Scheme 3.
Dithia[3.3]metacyclophane 12 was synthesized with KOH under
the high dilution condition from 7 and 11. SMe derivative 13 was
obtained by Witting rearrangement reaction and confirmed its
SCHEME 2 Synthesis of starting materials.

3
76
K. Chifuku et al.
SCHEME 3 Synthesis of DHP derivatives 1a and 2a.
1
structure by H-NMR and H-H COSY, H-H NOESY spectra. The
structure of 13 is shown in Figure 3. Bis-sulfonium salt derivative
1
5 was continuously produced by treating with dimethoxycarbonium
tetrafluoroborate 14. Hofmann elimination reaction of 15 by using
t-BuOK gave DHP derivative 2a which have a -SMe group. In the case
of using NaH, DHP derivative 1a was yielded. It was expected that
Hofmann elimination reaction of 15 produced MCPDs 1b and 2b,
and following thermal isomerization of the MCPDs 1b and 2b gave
DHPs 1a and 2a, respectively. Since both 1a and 2a were unstable
FIGURE 3 Structure of Sme derivative 13.

Dihydropyrene Containing a Nitrogen Atom
377
FIGURE 4 UV-Vis spectra of 1a (cyclohexane, 2.12 ꢁ 10ꢃ5 mol/l).
on silica gel, alumina, under the acid condition, they were 8.4% and
.7% yield, respectively. Structures of 1a and 2a were confirmed by
2
1
H-NMR and H-H COSY, H-H NOESY spectra.
UV-Vis spectra of 1a and 3a are shown in Figures 4 and 5. Absorp-
tion maximum of 1a shifted to the longer wavelength than that of 3a.
Energy gap between HOMO and LUMO of 1a and 3a calculated
with AM1 (software; Hyperchem Ver 5.1 for windows) is shown in
Figure 6.
As show in Figure 6, energy gap of 1a was smaller than that of 3a
about 0.78 eV by AM1 calculation. This calculation was supported by
UV-Vis spectra, in which absorption maximum of 1a shift to the longer
wavelength than that of 3a.
The optimized structures of 1a and 3a with AM1 (software;
Hyperchem Ver 5.1 for windows) are shown in Figures 7 and 8.
While the internal methyl groups of 3a locate at the center of 14p
annulene ring, 1a is the bowl type structure and the internal methyl
group of 1a shifts from the center of the 14p annulene ring.
Chemical shifts of the internal methyl groups and aromatic protons
of various DHP derivatives are shown in Table 1.
The peaks of internal methyl groups of 1a and 2a shifted the lower
magnetic field than that of 3a. The quantities of the chemical shifts
were not so remarkable compared with 16a. According to optimized

3
78
K. Chifuku et al.
FIGURE 5 UV-Vis spectra of 3a (cyclohexane, 1.80 ꢁ 10ꢃ5 mol/l).
structures of 1a and 3a, it is suggested that the low field shift was
depend on the position of internal methyl groups which located at
the out of center of 14p annulene ring for DHP derivatives [12,13].
Thermal isomerization from 1b to 1a was confirmed by the syn-
thetic procedure of 1a by Hofmann elimination of 15.
When C D solution of 1a was irradiated by visible light from the
6
6
halogen lamp (500 W), the C D insoluble material was generated.
6
6
1
When H-NMR spectrum of C D insoluble material was measured
6
6
FIGURE 6 Energy gaps of DHP 1a and 3a.

Dihydropyrene Containing a Nitrogen Atom
379
FIGURE 7 Optimized structure of 1a (AM1, HyperChem Pro Ver 5.1 for
Windows).
in CDCl , no peak of 1a and 1b was detected and broad peaks were
3
observed.
CONCLUSIONS
DHP derivatives 1a and 2a replaced with a nitrogen atom at 10c-
position was synthesized. Absorption maximum of 1a shifted to the
FIGURE 8 Optimized structure of 3a (AM1, HyperChem Pro Ver 5.1 for
Windows).

3
80
K. Chifuku et al.
TABLE 1 Chemical Shifts of Internal Methyl Groups and Aromatic-Protons
FIGURE 9 Photoisomerization of 1a.
longer wavelength compared with them of 3a. According to structural
optimization by AM1, structure of DHP 1a was not suggested the
plane type structure but the bowl type structure. Photo isomerization
to 1b from 1a was not observed. The irradiation of visible light seems
to cause polymerization of 1a (Fig. 9).
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[
4] Murphy, R. S., Chen, Y., Ward, T. R., Mitchell, R. H., & Bohne, C. (1999). Chem.
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[
[
[
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Dihydropyrene Containing a Nitrogen Atom
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[
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