Synthesis and properties of a 1,3-thiazole extended p- terphenoquinone. A New sp2 nitrogen atom-containing terquinone derivative

Article abstract of DOI:10.1246/bcsj.80.1402

2,5-Bis(3,5-di-tert-bufyl-4-oxo-2,5-cyclohexadien-1-ylidene)-2, 5-dihydrothiazole, which is to our knowledge, the first p-terphenoquinone incorporating a 1,3-thiazole ring, had a sharp and strong absorption in the visible region and good electron affinity enhanced by sp² nitrogen atom. Alkali-metal reduction afforded the corresponding dianion, which showed strong fluorescence.

Full text of DOI:10.1246/bcsj.80.1402

1402 Short Articles
Bull. Chem. Soc. Jpn. Vol. 80, No. 7, 1402–1404 (2007)
tBu
tBu
4'
tBu
tBu
N
6"
6
2'
1"
2"
Synthesis and Properties of
a 1,3-Thiazole Extended p-
Terphenoquinone. A New sp2
Nitrogen Atom-Containing
Terquinone Derivative
4"
4
X
S
1
5'
1
O
O
O
O
2
tBu
tBu
tBu
tBu
4: X = CH=CH
5: X = S
6: X = O
Chart 1. Thiazole-extended p-terphenoquinone 1 and other
terquinones.
ꢀ
Naoaki Imai, Kouzou Matsumoto,
tBu
N
Hiroyuki Kurata, Hideki Takakuwa,
N
ii)
i)
S
OH
Br
Takeshi Kawase, and Masaji Oda
S
89%
74%
tBu
Department of Chemistry, Graduate School of Science,
Osaka University, Toyonaka, Osaka 560-0043
2
tBu
tBu
N
S
iii)
85%
Received December 8, 2006; E-mail: kurata@chem.sci.osaka-
u.ac.jp
1
OH
O
OH
tBu
tBu
3
2,5-Bis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-
ylidene)-2,5-dihydrothiazole, which is to our knowledge, the
first p-terphenoquinone incorporating a 1,3-thiazole ring, had
a sharp and strong absorption in the visible region and good
electron affinity enhanced by sp2 nitrogen atom. Alkali-metal
reduction afforded the corresponding dianion, which showed
strong fluorescence.
Scheme 1. Synthesis of 1. Reagents and conditions: i) 3,5-
di-tert-butyl-4-hydroxyphenylboronic acid, Pd(PPh3)4,
K2CO3, DME, H2O; reflux, 16h; ii) 2.2 equiv of n-BuLi/
ether, ꢁ78 ꢂC, 1 h, then 2,6-di-tert-butylbenzoquinone;
iii) excess anhyd. CuSO4, toluene, reflux, 16 h.
however, we thought that Suzuki–Miyaura coupling would
be a better method. Pd0-catalyzed cross-coupling of 2-bromo-
thiazole and 3,5-di-tert-butyl-4-hydoxyphenylboronic acid af-
forded 2 in 74% yield. Then, we tried to introduce one more
phenol ring to 2 via bromination and Suzuki–Miyaura cou-
pling. Bromination of the thiazole ring, however, did not occur
probably because of a competitive electron-transfer reaction.
We, thus, applied a lithiation-functionalization protocol. Di-
lithiation of 2 was carried out by treatment with two equiva-
lents of butyllithium in THF at ꢁ78 ꢂC, and the dilithio com-
pound reacted with 2,6-di-tert-butylbenzoquinone to give 3 in
89% yield. Initially, we planned to reduce 3 to the correspond-
ing bis-phenol, but found that 3 underwent dehydration to form
quinone 1. The NMR sample of 3 in CDCl3 turned purple after
several days, and the signals of 1 were observed in its spec-
trum, probably because of contamination of the solvent by
small amount of acid. Dehydration of 3, therefore, was carried
out by treatment with anhydrous CuSO4 in toluene,11 and 1
was obtained in 85% yield.
Extended quinones have attracted considerable attention
from the viewpoints of their structural, physicochemical, and
especially, electrochemical properties.1 In particular, p-qui-
nones incorporating five-membered heteroaromatics have been
extensively studied. Thiophene-, furan-, selenole-, telluro-
phene-, and N-methylpyrrole-incorporated p-terpheno- and/
or quaterphenoquinone derivatives have been synthesized.
They exhibit amphoteric redox properties as well as potentials
for use as novel dyestuffs and in photoelectronic devices.2–6
Although the synthesis of oxadiazole- and thiadiazole-inserted
derivatives has been reported in a Japanese patent,7 derivatives
extended with a 1,3-thiazole ring have remained unknown.8
The electron-withdrawing 1,3-thiazole ring should increase
the acceptor ability of the quinones, while the nitrogen atom
should act as a functional part for intermolecular interactions,
such as the formation of metal complexes and supramolecules
having hydrogen bonds. Furthermore, thiazole-containing ꢀ-
systems have been investigated as n-type organic field-effect
transistors.9 In this context, we designed a new p-terphenoqui-
none derivative containing a 1,3-thiazole ring, 2,5-bis(3,5-di-
tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-2,5-dihydro-
thiazole (1), and here report its facile synthesis and fundamen-
tal properties (Chart 1).
Terquinone 1 was isolated green needles with golden metal-
lic luster and was deep purple in solution, with good air and
thermal stability. Well-resolved signals were observed in H
1
and 13C NMR spectra, indicating negligible contribution of di-
radical character on 1 (Table 1). The proton on the thiazole
ring (H40) was observed at a significantly low magnetic field
(ꢁ 8.76), which is caused by the electron-withdrawing effect
of the adjacent sp2-nitrogen atom as well as the two quinone
methide units. Among the non-equivalent four protons of
six-membered rings, H6 was shifted remarkably downfield
(ꢁ 8.07) compared to the other three protons, probably because
of the anisotropic effect of the nitrogen atom. 13C chemical
Synthesis of 1 is outlined in Scheme 1. It is thought that
2-(3,5-di-tert-butyl-4-hydroxyphenyl)thiazole (2) is a key in-
termediate, because 2 is not only the precursor for 1 but also
for other quinonoid compounds containing a thiazole unit.
Two-step synthesis of 2 has been reported in a U.S. Patent;10
Published on the web July 11, 2007; doi:10.1246/bcsj.80.1402

Bull. Chem. Soc. Jpn. Vol. 80, No. 7 (2007)
Ó 2007 The Chemical Society of Japan 1403
1
Table 1. Selected H and 13C NMR Spectral Dataa) of 1
tBu
tBu
N
Na/THF
(2e)
Position
200
S
1
O
O
2
6
40
600
7.51d)
4 and 400
tBu
tBu
1Hb)
7.25d)
8.07d)
8.76
7.15d)
12-
13Cc) 127.67 126.70 156.74 129.78 124.80
186.39
185.82
Scheme 2. Alkali-metal reduction of 1.
a) In CDCl3. The chemical shift assignment was determined
by COSY, NOESY, HMQC, and HMBC techniques. b) ꢁ/
ppm in 600 MHz. c) ꢁ/ppm in 150 MHz. d) Doublet, J ¼
2:5 Hz.
3
2
1
0
Abs.
Int. (a.u.)
10
6
300
400
500
600
700
ε/104
wavelength/nm
Fig. 2. UV–vis and emission spectra of dianion 12ꢁ in THF.
2
Alkali-metal reduction was performed for the generation
of the dianion of 1. In a degassed THF solution, 1 was reduced
by using with a sodium mirror. The reaction was monitored by
the change in UV–vis spectra. As the reaction proceeds, the
absorption of 1 gradually decreased and a new absorption at
350–450 nm appeared, thus indicating the formation of dianion
12ꢁ by electronic reduction (Scheme 2). The solution color
changed from deep purple to yellow. The final UV–vis spec-
trum is shown in Fig. 2 (ꢂmax ¼ 419 and 332 nm). Interesting-
ly, the solution of 12ꢁ exhibited strong fluorescence. The emis-
sion spectrum is also shown in Fig. 2, and the first and second
emission maxima were 475 and 497 nm, respectively.14
In conclusion, a new p-terphenoquinone extended with a
1,3-thiazole ring 1 was synthesized in three steps from 2-bro-
mothiazole. Facile di-lithiation of the key intermediate 2
should be a useful synthetic tool for a variety of novel thia-
zole-containing quinonoid compounds. Terquinone 1 showed
a sharp and strong absorption in the visible region, consider-
ably low reduction potentials in the cyclic voltammetry, and
strong fluorescence in the dianion state, which indicates that
1 has the potential for use in functionalized organic materials.
300
500
700
900
wavelength/nm
Fig. 1. UV–vis spectrum of 1 in CH2Cl2.
Table 2. Redox Potentialsa) of 1 and 5
E2ox E1ox
+1.68b) +1.38b)
E1red
E2red
1
5
ꢁ0:44
ꢁ0:63
ꢁ0:65
ꢁ0:79
+1.03
a) In CH2Cl2. b) V vs. Ag/Agþ in 0.1 M n-Bu4NClO4/CH2Cl2
at rt, scan rate 100 mV sꢁ1, ferrocene = +0.41 V. c) Peak
potential.
shifts of carbonyl carbons (C4 and C400) were comparable to
those of the benzoquinonoid,12 thienoquinonoid,2 and furoqui-
nonoid4 isomers (4, 5, and 6 in Chart 1: ꢁ 186.06, 185.81, and
185.72, respectively). Two pinch bonds of 1, C1–C20 and C50–
C100, can easily rotate; their rotational barriers (ꢀGz) were
estimated to be 85:4 ꢃ 0:8 and 78:7 ꢃ 0:8 kJ molꢁ1 respective-
ly, by the measurement of the coalescence phenomena among
signals of the tert-butyl protons.
Experimental
UV–vis spectrum of 1 is shown in Fig. 1. A sharp and
strong absorption was observed at ꢂmax(CH2Cl2) = 578 nm,
which is consistent with those of 4, 5, and 6. The absorption
end extends to the near-infrared region (700 nm). The longest
absorption maxima of 1 showed a slight bathochromic shift as
compared to that of 5 (ꢂmax(CH2Cl2) = 568 nm).13
Electrochemical properties of 1 were studied using cyclic
voltammetry. For comparison, the redox potentials of 5 were
measured under the same conditions, and the data are summa-
rized in Table 2. Compound 1 showed two sets of reversible
reduction waves, of which the first and second reduction
potentials were more positive than those of 5. This indicates
that introducing an electron-withdrawing 1,3-thiazole unit to
a quinone skeleton is an effective way of increasing its elec-
tron affinity. Whereas 5 showed a reversible oxidation wave
at a relatively low potential, 1 showed two oxidation peaks
and both of them were irreversible.
Melting points were measured on a Yanaco MP 500D apparatus
and were uncorrected. Mass spectra were recorded with a JEOL
SX-102 instrument by EI or FAB method. Infrared spectra were
recorded on a Perkin-Elmer 1650 FT-IR spectrophotometer in
KBr disks and only significant absorption bands are reported.
UV–vis absorption spectra were obtained on a Jasco V-570 spec-
trophotometer. 1H and 13C NMR spectra were measured on Varian
UNITY plus 600 (600 MHz), JEOL GSX-400 (400 MHz), or
JEOL EX-270 (270 MHz) instrument, and recorded in ꢁ value
with tetramethylsilane as an internal standard. Cyclic voltammetry
was performed on a BAS CV-50W voltammetric analyzer. Micro-
analyses were performed at the Elemental Analysis Center,
Faculty of Science, Osaka University.
2-(3,5-Di-tert-butyl-4-hydroxyphenyl)thiazole (2). 3,5-Di-tert-
butyl-4-hydoxyphenylboronic acid (500 mg, 2.0 mmol), sodium car-
bonate (1.27 g, 12 mmol), and water (4 mL) were added to a solution
of 2-bromothiazole (274 mg, 1.7 mmol) and Pd(PPh3)4 (115 mg, 0.1

1404 H. Kurata et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 7 (2007)
mmol) in 1,2-dimethoxyethane (10 mL) under nitrogen atmosphere.
The mixture was heated at reflux for 16 h. After cooling to room
temperature, the mixture was quenched with 1 M (=1 molLꢁ1) HCl
(10 mL) and extracted with diethyl ether (20 mL ꢄ 3). The com-
bined organic phase was washed with water and brine and dried
with anhydrous Na2SO4. After evaporation of solvent in vacuo, the
residue was purified by column chromatography (SiO2, 50 g, eluent;
10% ethyl acetate/hexane) to give 2 (357 mg, 74%): colorless plates
(benzene/hexane); mp 127–128 ꢂC; MS(EI) m=z 289 (Mþ, 100%),
163.48, 156.74, 152.56, 151.62, 148.73, 148.58, 148.44, 129.78,
128.86, 128.46, 127.67, 126.70, 124.80, 36.13, 36.02, 35.81,
35.79, 29.74, 29.67, 29.64, 28.60; UV–vis. (CH2Cl2) ꢂmax/nm
(log ") 627 (4.51), 578 (4.93), 540sh (4.70), 500sh (4.27), 327
(3.89), 262 (3.88), IR (KBr) ꢃ/cmꢁ1 2956m, 1590s(CO), 1454w,
1387w, 1361m, 1331w, 1253w, 1126m, 1086w, 1033w, 884w,
859m, 816w, 716w; Found: C, 75.50; H, 8.45; N, 2.84%. Calcd
for C31H41NO2S: C, 75.72; H, 8.40; N, 2.85%.
1
274 [(M ꢁ CH3)þ, 90%]; HNMR (400 MHz, CDCl3) ꢁ 7.80 (d,
References
J ¼ 3:3 Hz, 1H), 7.78 (s, 2H), 7.22 (d, J ¼ 3:3 Hz, 1H), 5.46 (s,
1H), 1.50 (s, 18H); 13C NMR (67.8 MHz, CDCl3) ꢁ 169.67, 155.76,
143.31, 136.52, 125.39, 123.81, 117.50, 34.42, 30.21; IR (KBr)
ꢃ/cmꢁ1 3584s (OH), 2956s, 1434s, 1388s, 1237s, 1118m, 921m,
880m, 849s, 811w, 769w, 704w, 604m, 546w, 512w; Found: C,
70.49; H, 8.07; N, 4.87%. Calcd for C17H23NOS: C, 70.55; H,
8.01; N, 4.84%.
1
a) The Chemistry of Quinonoid Compounds, ed. by S.
Patai, Wiley, London, 1974. b) The Chemistry of Quinonoid
Compound, ed. by S. Patai, Z. Rappoport, Wiley, Chichester,
1988, Vol. II.
2 a) K. Takahashi, T. Suzuki, J. Am. Chem. Soc. 1989, 111,
5483. b) K. Takahashi, T. Suzuki, K. Akiyama, Y. Ikegami, Y.
2-(3,5-Di-tert-butyl-4-hydroxyphenyl)-5-(3,5-di-tert-butyl-1-
hydroxy-4-oxo-2,5-cyclohexadienyl)thiazole (3). A 1.6 M solu-
tion of butyllithium in hexane (1.5 mL, 2.4 mmol) was added
dropwise to a solution of 2 (287 mg, 1.0 mmol) in THF (7.5 mL)
at ꢁ78 ꢂC. After stirring at ꢁ78 ꢂC for 1 h, a solution of 2,6-di-
tert-butylbenzoquinone (242 mg, 1.1 mmol) in THF (5 mL) was
added, and then the mixture was stirred at 0 ꢂC for 1.5 h. After hy-
drolysis with saturated ammonium chloride aqueous solution, the
mixture was extracted with ethyl acetate (20 mL ꢄ 3), washed
with water and brine, and dried with Na2SO4. The solvent was
evaporated in vacuo, and the residue was washed with hexane
to give 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-5-(3,5-di-tert-bu-
tyl-1-hydroxy-4-oxo-2,5-cyclohexadienyl)thiazole (455 mg, 89%).
This compound was used for the next reaction without further
Fukazawa, J. Am. Chem. Soc. 1991, 113, 4576.
3
4
K. Takahashi, T. Sakai, Chem. Lett. 1993, 157.
a) K. Takahashi, A. Gunji, K. Akiyama, Chem. Lett. 1994,
863. b) K. Takahashi, A. Gunji, Heterocycles 1996, 43, 941.
K. Takahashi, A. Gunji, K. Yanagi, M. Miki, J. Org. Chem.
1996, 61, 4784.
5
6
a) R. Tamura, Y. Nagata, H. Shimizu, A. Matsumoto, N.
Ono, A. Kamimura, K. Hori, Adv. Mater. 1993, 5, 719. b) R.
Tamura, H. Takasuka, Y. Nagata, N. Azuma, A. Matsumoto, Y.
Sadaoka, A. Gunji, K. Takahashi, A. Kamimura, K. Hori, Mol.
Cryst. Liq. Cryst. 1996, 278, 139.
7
S. Hirano, Jpn. Kokai Tokkyo Koho JP 08020580, 1996;
Chem. Abstr. 1996, 115, 281609.
A bithiazole-extended TCNQ type have been known: K.
8
1
purification; colorless powder; mp > 150 ꢂC (decomp.); H NMR
Suzuki, M. Tomura, S. Tanaka, Y. Yamashita, Tetrahedron Lett.
2000, 41, 8359.
(270 MHz, CDCl3) ꢁ 7.72 (s, 2H), 7.55 (s, 1H), 6.71 (s, 2H), 5.48
(s, 1H), 1.93 (brs, 1H), 1.48 (s, 18H), 1.24 (s, 18H); 13C NMR
(67.8 MHz, CDCl3) ꢁ 185.70, 170.19, 156.08, 145.97, 140.43,
140.00, 139.50, 136.59, 125.12, 123.70, 68.49, 34.84, 34.43,
30.20, 29.36; HRMS Found: m=z 509.2968. Calcd for C31H43-
NO3S: [Mþ], 509.2964.
9
a) S. Ando, J. Nishida, E. Fujiwara, H. Tada, Y. Inoue,
S. Tokito, Y. Yamashita, Synth. Met. 2006, 156, 327. b) S. Ando,
R. Murakami, J. Nishida, H. Tada, Y. Inoue, S. Tokito, Y.
Yamashita, J. Am. Chem. Soc. 2005, 127, 14996.
10 G. G. I. Moore, US Patent 1985, Chem. Abstr. 1985, 104,
34081.
11 H. Kurata, M. Monden, T. Kawase, M. Oda, Tetrahedron
Lett. 1998, 39, 7135.
12 a) R. West, J. A. Jorgenson, K. L. Stearly, J. C. Calabrese,
J. Chem. Soc., Chem. Commun. 1991, 1234. b) P. Boldt, D.
2,5-Bis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-
2,5-dihydrothiazole (1). Compound 3 (50 mg, 0.1 mmol) was
added to a suspension of well-dried anhydrous CuSO4 (500 mg,
3.1 mmol) in toluene (10 mL) under a nitrogen atmosphere. The
mixture was then refluxed for 16 h. After removal of inorganic
materials by filtration, the filtrate was evaporated in vacuo, and
the residue was purified by column chromatography (SiO2, 20 g,
eluent; 10% ethyl acetate/hexane) to give 1 (42 mg, 85%): metal-
lic green needles (benzene–hexane); mp 248–249 ꢂC (decomp.)
Bruhnke, F. Gerson, M. Scholz, P. G. Jones, F. Bar, Helv. Chim.
Acta 1993, 76, 1739.
¨
13 Compound 5 was prepared and UV–vis spectrum was
measured under the same condition as 1.
14 The quantum yield could not obtain because the determina-
tion of the solution concentration and the reduction conversion
was difficult.
1
MS (FAB) m=z 494.4 [(M + H)þ]; H NMR (600 MHz, CDCl3)
ꢁ 8.76 (s, 1H), 8.07 (d, J ¼ 2:5 Hz, 1H), 7.51 (d, J ¼ 2:5 Hz, 1H),
7.25 (d, J ¼ 2:5 Hz, 1H), 7.15 (d, J ¼ 2:5 Hz, 1H), 1.38 (s, 9H),
1.37 (s, 27H); 13C NMR (150 MHz, CDCl3) ꢁ 186.39, 185.82,