Preparation of novel push-pull benzothiazole derivatives with reverse polarity: Compounds with potential non-linear optic application

Article abstract of DOI:10.1055/s-2004-837309

The hitherto unknown 6-dimethylaminobenzothiazole-2-carbaldehyde was prepared as a starting compound for the synthesis of novel push-pull benzothiazole derivatives with reverse polarity. These compounds are substituted at the 2-position by strong electron-acceptor groups and at the 6-position by NMe₂ as strong electron-donor. The new method for synthesis of 6-dimethylaminobenzothiazole involved the successful use of sonochemical reductive methylation. Expected non-linear optical properties of target molecules were studied by EFISH method.

Full text of DOI:10.1055/s-2004-837309

6
00
PAPER
Preparation of Novel Push-Pull Benzothiazole Derivatives with Reverse
Polarity: Compounds with Potential Non-Linear Optic Application
Push-Pull Ben
e
zothiazole
t
erivat
e
ives
w
ith R
r
everse Polarit yH robárik,* Ivica Sigmundová, Pavol Zahradník*
Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University Bratislava, Mlynská Dolina, 84215 Bratislava,
Slovakia
Fax +421(2)60296690; E-mail: peter.hrobarik@savba.sk; E-mail: zahradnik@fns.uniba.sk
Received 5 October 2004
a series of differently donor-acceptor substituted NLO-
Abstract: The hitherto unknown 6-dimethylaminobenzothiazole-
phores containing the benzothiazole moiety. Two types of
push-pull benzothiazoles according to the direction of di-
pole moment have been calculated: 1) the compounds
2
-carbaldehyde was prepared as a starting compound for the synthe-
sis of novel push-pull benzothiazole derivatives with reverse polar-
ity. These compounds are substituted at the 2-position by strong
electron-acceptor groups and at the 6-position by NMe as strong with normal polarity where the electron-acceptor group is
2
electron-donor. The new method for synthesis of 6-dimethylami- bonded to the heterocyclic benzene ring, the p-conjugated
nobenzothiazole involved the successful use of sonochemical re-
spacer is linked to the C-2 of the heterocycle and the elec-
ductive methylation. Expected non-linear optical properties of
tron-donor group stands on the opposite site of the spacer,
target molecules were studied by EFISH method.
and 2) the changed position for electron-donor and elec-
tron-acceptor groups, respectively, is characteristic for the
benzothiazole derivatives with reverse polarity (Figure 1).
Key words: benzothiazole, non-linear optics, push-pull system, re-
verse polarity, hyperpolarizability
The growing interest in organic materials for electro-optic
device applications (ultrafast analog-to-digital converters,
1
–5
ultrafast image processing, optical data storage) has led
to the development of non-linear optic (NLO) chro-
mophores possessing large molecular second order non-
linearity b. Most attempts to design chromophores with
6
large b have been based upon push-pull compounds. The
general structure of this type of chromophores is D-p-A,
where the electron-donor (D) and electron-acceptor (A)
groups are linked by a p-conjugated spacer. The donor
and acceptor substituents provide the requisite ground-
state charge asymmetry, whereas the p-conjugation moi-
ety serves as a pathway for the redistribution of electric
charges under the influence of electric fields. Many of
these donor-p-acceptor systems are substituted benzenes,
stilbenes and azostilbenes. A general structure-property
relationship for these donor-acceptor systems has been
well understood, although some further modifications and
improvements are still ongoing. Replacement of one or
both benzene rings of stilbene with more easily delocaliz-
able heteroaromatics, such as pyrrole, furan, thiophene or
thiazole, leads to enhanced hyperpolarizabilities.7 For
the practical application of NLO materials, both high hy-
perpolarizability and thermal stability are required, be-
cause chromophores must be stable at all temperatures
Figure 1 Benzothiazole derived NLO-phores with normal and re-
verse polarity (in respect to natural dipole moment of benzothiazole)
It is worth mentioning that benzothiazole derivatives pub-
13,14
lished up to now as NLO-phores have normal polarity.
Our theoretical results predict that benzothiazole deriva-
tives with reverse polarity could have larger b when a
strong acceptor is directly bonded to the C-2 (with or
without short vinyl spacer).
–11
The most worthwhile targets for synthesis in terms of
highest hyperpolarizabilities b were benzothiazole deriv-
atives with reverse polarity containing strong acceptor
group (dicyanovinyl or tricyanovinyl) in position 2, and a
p-dialkylaminostyryl or dialkylaminoheteroarylvinyl
group in position 6 of the benzothiazole ring. In order to
verify our theoretical prediction, we tried to prepare 6-
dimethylaminobenzothiazole-2-carbaldehyde, which was
not described in the literature yet. This aldehyde can serve
as a starting compound for syntheses of various push-pull
benzothiazole derivatives with interesting properties.
1
that the system encounters. In this respect, good candi-
dates are benzothiazole derivatives. In our previous theo-
1
2
retical work, we presented semi-empirical (ZINDO-
SOS) as well as ab initio (HF-DDRPA/6-31G*) calcula-
tions on molecular quadratic hyperpolarizabilities b of
SYNTHESIS 2005, No. 4, pp 0600–0604
x
x
.
x
x
.2
0
0
5
Advanced online publication: 23.12.2004
DOI: 10.1055/s-2004-837309; Art ID: P11804SS
Georg Thieme Verlag Stuttgart · New York
©

PAPER
Push-Pull Benzothiazole Derivatives with Reverse Polarity
601
21
The synthesis is described in Scheme 1. Starting, 6-ni- 2-carbaldehyde was synthesized in this way. Compound
trobenzothiazole (1) was prepared according to the litera- 6 was prepared from 2-methyl-6-nitrobenzothiazole in the
ture procedure by nitration of benzothiazole with fuming same way as compound 2 from 6-nitrobenzothiazole. The
1
5
nitric acid. The reduction of 6-nitrobenzothiazole (1) reductive methylation of 6 was successfully carried out by
was improved by using ultrasound. An attempt at reduc- the 10 equivalents of formaldehyde and NaBH in 15 min-
4
tive methylation of NH group with a 10-fold excess of utes. It is interesting that methyl group in position 2 pro-
2
1
6
formaldehyde and NaBH4 led to an inseparable mixture tects imine double bond in thiazole ring against reduction
of 3 and the major product 5 (Scheme 2). A similar type with NaBH (cf. Scheme 2). However, the bromination of
4
of ring saturation (as in the case of 5) had been observed 7 by NBS afforded surprisingly the unknown, 7-bromo-6-
on reduction of 3-methylbenzothiazolium salts with dimethylamino-2-methylbenzothiazole (8) (Scheme 3).
1
7
NaBH CN. Only if the reductive agent NaBH was re-
3
4
placed by Fe/H SO under sonication, an acceptable yield
2
4
(
45%) of the compound 3 was achieved. We were unsuc-
cessful when we tried to prepare 3 by a one-pot reaction
from compound 1. The reduction of nitro group under
sonication worked only in polar ethanol, while reductive
methylation did not proceed under these conditions. The
isolated 6-dimethylaminobenzothiazole (3) was convert-
ed to the corresponding 2-carbaldehyde 4 in good yield by
1
8
reaction with BuLi followed by reaction with DMF and
hydrolysis (Scheme 1). This is a new way of synthesis of
substituted benzothiazole-2-carbaldehyde derivatives,
which were up to now prepared by oxidation of 2-methyl
1
9
group using SeO2 or by oxidative cleavage of double
2
0
bond attached to C-2 of benzothiazole. Disadvantages of Scheme 3
previous methods were low yields, toxicity of selenium
and/or inaccessibility of 6-dimethylamino-2-vinylben-
zothiazole derivatives.
The target compounds 9 and 10 with reverse polarity were
prepared by the condensation of carbaldehyde 4 with ma-
lononitrile and/or 2-(phenylsulfonyl)acetonitrile, respec-
tively (Scheme 4).
Scheme 1
Scheme 4
Another type of push-pull bis-benzothiazole was obtained
by the condensation of carbaldehyde 4 with 6-cyano-2-
methylbenzothiazole (11) (Scheme 5). Compound 11 was
prepared earlier from 6-amino-2-methylbenzothiazole (6)
22
by diazotation and Sandmeyer reaction in 57% yield.
Compound 11 was also used for the preparation of new
compound with normal polarity 2-[2-(4-dimethylami-
nophenyl)vinyl]benzotiazole-6-carbonitrile (13) by con-
Scheme 2
densation
Scheme 5).
with
4-dimethylaminobenzaldehyde
Another way of preparing aldehyde 4 could be via bromi-
nation of 2-methyl-6-dimethylaminobenzothiazole (7)
(
followed by hydrolysis of intermediate geminal 2-dibro- Compounds 9, 10 and 13 were subjected to EFISH
momethylbenzothiazole. A similar unsubstituted thiazole- measurements23 of first hyperpolarizability and dipole
Synthesis 2005, No. 4, 600–604 © Thieme Stuttgart · New York

6
02
P. Hrobárik et al.
PAPER
Figure 2 EFISH signals obtained from acetone solutions of 9
3
3
(
c = 4.12 mmol/dm ) and 13 (c = 5.7 mmol/dm ) at 1064 nm; measu-
red data are given in dotted lines, calculated values in solid ones.
The mb values were measured in 1,4-dioxane and/or acetone by
electric-field induced second harmonic generation (EFISH) tech-
nique in the swivel cell. A Nd-YAG laser (l = 1064 nm) was used.
The measurement cell (standard optical cell, 100-OS-5 by Hellma,
Germany) was mounted on an electronically controlled rotary table.
Angular resolution was better than 0.1° and total travel was –25 to
Scheme 5
+
25°. All experimental data are referenced on p-nitroaniline in di-
–
47
–47
oxane 18.3 × 10 esu and/or in acetone 34.2 × 10 esu, respec-
tively.
moment mb (EFISH output is depicted in Figure 2). The
experimental results as well as calculated theoretical
1
2
values are presented in Table 1. Agreement between
theoretical and experimental values is quite good, with the
Sonochemical Reduction of 6-Nitrobenzothiazole Derivatives to
Amines; General Procedure
exception of compound 9. The discrepancy in this case To a mixture of 6-nitrobenzothiazole (1) or 2-substituted 6-ni-
can be explained by the strong absorption of compound 9 trobenzothiazole (27 mmol) and conc. HCl (3.8 mL, 44 mmol) in
8
0% EtOH (120 mL) was added powdered iron (6.0 g, 108 mmol).
at 532 nm, what is close to twice the exciting laser fre-
quency. In those cases the used theoretical method gives
larger b-values. Unfortunately, up to now we have no
EFISH results for 12 (problem with solubility in acetone
or dioxane).
The reaction mixture was sonicated for 20 min (temperature at-
tained: 90 °C) and then cooled down to r.t. Precipitated of iron ox-
ides and hydroxy salts were removed by filtration and washed with
EtOH (2 × 30 mL). The solvent was removed from combined EtOH
solutions on a rotary vacuum evaporator and the solid residue was
extracted into a heterogeneous mixture of EtOAc and 10% aq solu-
tion of Na CO . EtOAc extract was dried (Na SO ) and the solvent
Table 1 Experimental EFISH and Calculated ZINDO Data (Includ-
2
3
2
4
12b
ing Solvent Effect) of New Benzothiazole Derivatives
was removed under vacuum. The crude product was purified by
short-column chromatography [SiO , i-hexane (2-methylpentane)–
EtOAc, 2:1].
2
Product
Solvent
acetone
acetone
dioxane
acetone
mbexp (10–48 esu) mbZINDO (10–48 esu)
9
5050
6100
1200
3180
6750
6704
1065
2970
6
-Aminobenzothiazole (2)
Prepared from 6-nitrobenzothiazole (1; 4.8 g); yield: 3.50 g (88%),
mp 86–87 °C (Lit.
1
1
1
0
3
3
2
4b
mp 84–85 °C); R 0.10 (SiO , i-hexane–
f 2
EtOAc, 1:1).
1
H NMR (300 MHz, CDCl /TMS): d = 8.70 (s, 1 H, H-2), 7.89 (d,
3
1
H, J = 8.9 Hz, H-4), 7.16 (d, 1 H, J = 2.2 Hz, H-7), 6.87 (dd, 1 H,
J = 8.9, 2.2 Hz, H-5), 3.86 (br s, 2 H, NH2).
NMR spectra were recorded with a Varian Gemini 2000 spectro-
6-Amino-2-methylbenzothiazole (6)
1
13
meter at 300 MHz for H and 75 MHz for C in CDCl with TMS
Prepared from 6-nitro-2-methylbenzothiazole (5.2 g); yield: 3.80 g
3
2
4a
as an internal standard; chemical shifts d are given in ppm; coupling
constants J are given in Hz. UV/Vis absorption spectra were taken
(86%), mp 125–126 °C (Lit. mp 125–127 °C); R 0.11 (SiO ,
f 2
i-hexane–EtOAc, 1:1).
on a Hewlett-Packard Diode Array 8245 in CHCl solution. IR
1
3
H NMR (300 MHz, CDCl /TMS): d = 7.70 (d, 1H, J = 8.8 Hz, H-
3
spectra were recorded on a Perkin-Elmer 781 in CHCl . Melting
3
4
5
), 7.06 (d, 1 H, J = 2.8 Hz, H-7), 6.79 (dd, 1 H, J = 8.8, 2.8 Hz, H-
points were determined using a Kofler apparatus and are uncorrect-
), 3.78 (s, 2 H, NH ), 2.75 (s, 3 H, CH ).
2
3
ed. TLC was carried out on SiO (Lachema/UV) and spots were de-
2
tected with UV light (254 nm). Flash chromatography was carried
6
-Dimethylaminobenzothiazole (3)
out on SiO (silica gel, Merck). Elemental analyses were recorded
2
A solution of 6-aminobenzothiazole (2; 3.0 g, 20.0 mmol) in THF
80 mL) was slowly added to a stirred mixture of 40% aq formalde-
hyde (15.4 mL, 200 mmol) and 4 M H SO (15 mL, 60 mmol). To
on a Carlo Erba CHN 1106. All sonochemical experiments were
carried out in a glass reactor fitted to an ultrasonic horn
ULTRAGEN (20 kHz, 300 W) under air.
(
2
4
the resultant mixture was added powdered iron (8.9 g, 160 mmol)
and the mixture was sonicated for 30 min. The precipitate of iron
Synthesis 2005, No. 4, 600–604 © Thieme Stuttgart · New York

PAPER
Push-Pull Benzothiazole Derivatives with Reverse Polarity
603
salts was removed by filtration and washed with EtOAc (2 × 20
mL). The combined organic solutions were made strongly basic
with 20% aq NaOH and extracted with EtOAc (2 × 100 mL). The
combined EtOAc extracts were dried (Na SO ) and the solvent was
i-hexane–EtOAc, 4:1) to give 8 (0.28 g, 52%) as a yellow-white
needles; mp 62–63 °C; R 0.54 (SiO , i-hexane–EtOAc, 3:1).
f
2
1
H NMR (300 MHz, CDCl /TMS): d = 7.81 (d, 1 H, J = 8.6 Hz, H-
3
2
4
4
), 7.23 (d, 1 H, J = 8.6 Hz, H-5), 2.85 [s, 6 H, N(CH ) ], 2.79 (s, 3
3 2
removed on the rotary vacuum evaporator. The oily residue was pu-
H, CH3).
rified by column chromatography (SiO , i-hexane–EtOAc, 4:1) to
2
1
3
2
5b
C NMR (75 MHz, CDCl /TMS): d = 165.79 (C-2), 149.28 (C),
give 3 (1.60 g, 45%) as white needles; mp 77–79 °C (Lit. mp 73–
3
1
4
48.58 (C), 140.93 (CS), 121.50 (CH), 119.01 (CH), 109.76 (CBr),
4.88 [N(CH ) ], 20.31 (CH ).
7
4 °C); R 0.41 (SiO , i-hexane–EtOAc, 3:1).
f 2
1
3
2
3
H NMR (300 MHz, CDCl /TMS): d = 8.67 (s, 1 H, H-2), 7.95 (d,
3
1
H, J = 8.8 Hz, H-4), 7.15 (d, 1 H, J = 2.2 Hz, H-7), 7.00 (dd, 1 H,
2
-(6-Dimethylaminobenzothiazol-2-ylmethylene)malononitrile
J = 8.8, 2.2 Hz, H-5), 3.03 [s, 6 H, N(CH ) ].
3
2
(
9)
A solution of 6-(dimethylamino)benzothiazol-2-carbaldehyde 4
6
-Dimethylaminobenzothiazole-2-carbaldehyde (4)
To a vigorously stirred solution of BuLi (4.2 mL, 1.6 M in hexane,
.70 mmol) in anhyd THF (20 mL) at –78 °C under N was added
(
(
0.21 g; 1.0 mmol), malononitrile (0.10 g, 1.5 mmol) and pyridine
0.2 mL) in propan-2-ol (12 mL) was stirred and refluxed for 30
6
2
min. The mixture was poured into H O (30 mL) and extracted with
2
slowly a solution of 6-dimethylaminobenzothiazole (3; 1.15 g, 6.45
mmol) in THF (10 mL). The reaction mixture was stirred, warmed
to –50 °C (temperature should not raise above –35 °C) and after 1 h
cooled to –78 °C. To the resulting solution of aryllithium salt was
added slowly anhyd DMF (2 mL). The solution was stirred for 1 h,
poured into H O (100 mL), neutralized with aq sat. solution of
NH Cl and subsequently extracted with EtOAc (2 × 100 mL). The
combined extracts were dried (Na SO ) and the solvent was re-
CHCl (3 × 20 mL). The combined extracts were dried (Na SO )
3
2
4
and the solvent was removed under vacuum. The residue was re-
crystallized from EtOH to give 9 (0.23 g, 90%) as dark-red crystals;
mp 218–219 °C; R 0.33 (SiO , i-hexane–EtOAc, 3:1).
f
2
–
1
IR (CHCl ): 2210 cm (C≡N).
3
2
1
4
H NMR (300 MHz, CDCl /TMS): d = 7.99 [s, 1 H, CH(CN) ], 7.99
3 2
(d, 1 H, J = 9.2 Hz, H-4), 7.08 (dd, 1 H, J = 9.2, 2.3 Hz, H-5), 7.01
2
4
moved under vacuum. The crude product was recrystallized from
EtOH to give 4 (1.05 g, 80%) as a yellow-brown needles.; mp 174–
1
(
d, 1 H, J = 2.3 Hz, H-7), 3.16 [s, 6 H, N(CH ) ].
3 2
1
3
C NMR (75 MHz, CDCl / TMS): d = 151.30 (C), 151.22 (C),
3
75 °C; R 0.46 (SiO , i-hexane–EtOAc, 3:1).
f 2
1
51.12 (CH), 145.54 (C), 141.60 (C), 126.45 (CH), 115.87 (CH),
–
1
IR (CHCl ): 1680s cm (C=O).
3
113.99 (C), 112.99 (C), 100.67 (CH), 81.65 (C), 40.88 [N(CH ) ].
3 2
1
H NMR (300 MHz, CDCl /TMS): d = 10.05 (s, 1 H, CHO), 8.02
3
–1
–1
3
UV (CHCl ): l = 530 nm (e = 42500 dm ·mol ·cm ).
3 max
(
(
1
d, 1 H, J = 9.9 Hz, H-4), 7.05 (dd, 1, H, J = 9.9, 2.4 Hz, H-5), 7.05
d, 1 H, J = 2.4 Hz, H-7), 3.11 [s, 6,H, N(CH ) ].
Anal. Calcd for C H N S: C, 61.40; H, 3.96; N, 22.03; S, 12.61.
1
3
10
4
3
2
Found: C, 61.24; H, 3.99; N, 21.88; S, 12.60.
3
C NMR (75 MHz, CDCl /TMS): d = 185.15 (CHO), 160.13 (C-2),
3
1
50.86 (C), 145.65 (C), 140.12 (Carom–S), 126.26 (CH), 114.90
2-Benzenesulfonyl-3-(6-dimethylaminobenzothiazol-2-yl)acry-
lonitrile (10)
To a solution of 6-dimethylaminobenzothiazole-2-carbaldehyde (4;
(CH), 101.75 (CH), 40.84 [N(CH ) ].
3 2
3
–1
–1
UV (CHCl ): l = 424 nm (e = 17800 dm ·mol ·cm ).
3
max
0
.10 g, 0.49 mmol) in MeOH (10 mL) was added 2-(phenylsulfo-
Anal. Calcd for C H N OS: C, 58.23; H, 4.89; N, 13.58. Found:
C, 58.15; H, 4.88; N, 13.37.
10
10
2
nyl)acetonitrile (0.10 g, 0.55 mmol) and solid NaOH (0.10 g, 2.5
mmol) as a base catalyst. The reaction mixture was stirred and re-
fluxed for 3 h. After cooling, the brown precipitate was collected by
filtration, dried and recrystallized from EtOH to give 10 (0.14 g,
6
-Dimethylamino-2-methylbenzothiazole (7)
A solution of 6-amino-2-methylbenzothiazole (6; 2.0 g, 12.2 mmol)
in THF (60 mL) was slowly added to a stirred mixture of 40% aq
formaldehyde (9.4 mL, 122 mmol) and 4 M H SO (12 mL, 48
7
8%) as red-brown crystals; mp 228–229 °C; R 0.23 (SiO , i-hex-
f 2
ane–EtOAc, 3:1);
2
4
–
1
IR (CHCl ): 2210 cm (C≡N).
mmol). To the resulting solution was added finely crushed NaBH4
4.62 g, 122 mmol) at such a rate that the temperature did not exceed
0 °C (Note: the reaction is strongly exothermic). After the addition
3
(
3
1H NMR (300 MHz, CDCl /TMS):
d
= 8.45 [s, 1 H,
3
CH(CN)SO Ph], 8.04 (dd, 2 Harom, J = 7.1, 1.7 Hz), 7.98 (d, 1 H,
2
was complete, the mixture was stirred for 15 min at r.t. and then was
made strongly basic with 20% aq NaOH. The resultant mixture was
extracted with EtOAc (3 × 50 mL). The combined EtOAc extracts
were washed with brine, dried (Na SO ) and the solvent was re-
J = 9.3 Hz, H-4), 7.59 (m, 3 Harom), 7.05 (dd, 1 H, J = 9.3, 2.2 Hz,
H-5), 7.00 (d, 1 H, J = 2.2 Hz, H-7), 3.13 [s, 6 H, N(CH ) ].
3
2
1
3
C NMR (75 MHz, CDCl /TMS): d = 151.01 (C), 150.83 (C),
3
2
4
1
1
45.57 (C), 143.87 (CH), 141.16 (C), 138.20 (C), 134.76 (CH),
29.85 (CH), 128.81 (CH), 126.00 (CH), 115.40 (CH), 115.02 (C),
moved on the rotary evaporator. The oily residue was purified by
column chromatography (SiO , i-hexane–EtOAc, 3:1) to give 7
2
2
5a
113.12 (C), 100.78 (CH), 40.76 [N(CH
UV (CHCl ): lmax = 514 nm (e = 36600 dm ·mol ·cm ).
Anal. Calcd for C18 : C, 58.52; H, 4.09; N, 11.37; S,
17.36. Found: C, 58.45; H, 4.09; N, 11.28; S, 17.11.
3 2
) ].
(
1.50 g, 64%) as colorless needles; mp 72–74 °C (Lit. mp 71 °C);
3
–1
–1
R 0.40 (SiO , i-hexane–EtOAc, 3:1).
3
f
2
1
H NMR (300 MHz, CDCl /TMS): d = 7.77 (d, 1 H, J = 9.3 Hz, H-
H N O S
15 3 2 2
3
4
5
), 7.06 (d, 1 H, J = 2.8 Hz, H-7), 6.92 (dd, 1 H, J = 9.3, 2.8 Hz, H-
), 3.00 [s, 6 H, N(CH ) ], 2.76 (s, 3 H, CH ).
3
2
3
2
-Methylbenzothiazole-6-carbonitrile (11)
To a stirred solution of 6-amino-2-methylbenzothiazole (6; 4.0 g;
0.024 mol) in 2.5 M aq H SO (20 mL, 0.05 mol) was added NaNO
(1.8 g, 0.026 mol) dissolved in H O (8 mL). The reaction tempera-
ture was maintained in the range of –2 up to 2 °C. After the addition
of NaNO , the mixture was partially neutralized by adding crushed
ice (ca. 10 g) and 10% aq solution Na CO (ca. 10 mL). The red di-
7
-Bromo-6-dimethylamino-2-methylbenzothiazole (8)
To a solution of 6-dimethylamino-2-methylbenzothiazole (7; 0.39
g, 2 mmol) in anhyd CCl (10 mL) was added N-bromosuccinimide
2
4
2
4
2
(
0.72 g, 4 mmol) and AIBN (0.02 g, 0.12 mmol). The mixture was
stirred at r.t. for 5 min and then refluxed for 40 min. After cooling
to r.t., the brown precipitate was collected by filtration and washed
with CCl . The combined CCl solutions were washed with aq 10%
2
2
3
azonium salt solution was slowly poured into a freshly prepared so-
lution of CuCN (2.50 g, 0.028 mol), NaCN (3.0 g, 0.061 mol) and
4
4
Na CO solution and the solvent was removed under vacuum. The
2
3
crude product was purified by column chromatography (SiO2,
NaOH (4.0 g, 0.100 mol) in H O (60 mL) in a large Erlenmeyer
2
Synthesis 2005, No. 4, 600–604 © Thieme Stuttgart · New York

6
04
P. Hrobárik et al.
PAPER
flask. The mixture was stirred at r.t. for 10 min, followed by stirring Acknowledgment
at 80 °C (Note: evolution of gaseous N , strong foaming) for 2 h.
2
This project was supported by the Ministry of Education, Slovak
Republic (grant VEGA 1/1374/04). We would like to thank Prof.
Walter M. Fabian and Dr. Renate Dworczak, Institute of Chemistry,
Karl-Franz University in Graz (Austria) for EFISH measurements.
After cooling, a black solid was collected by filtration and the mix-
ture was extracted with CHCl (50 mL). The CHCl extract was
3
3
dried (Na SO ) and the solvent was removed under vacuum. The
2
4
product 11 was obtained by vacuum sublimation (0.5 Torr/150 °C)
of the combined black solids as white needles (2.40 g, 57%); mp
1
43–144 °C (Lit.22 mp 144 °C); R 0.18 (SiO2, i-hexane–
f
References
EtOAc, 7:1).
1
(1) Dalton, L. Adv. Polym. Sci. 2002, 158, 1.
H NMR (300 MHz, CDCl /TMS): d = 8.17 (d, 1 H, J = 1.7 Hz, H-
3
(2) Marder, S. R.; Kippelen, B.; Jen, A. K. Y.; Peyghambarian,
N. D. Nature 1997, 388, 845.
7
5
), 8.02 (d, 1 H, J = 8.8 Hz, H-4), 7.71 (dd, 1 H, J = 8.8, 1.7 Hz, H-
), 2.90 (s, 3 H, CH3).
(
3) Alivisatos, A. P.; Barbara, P. F.; Castleman, A. W.; Chang,
J.; Dixon, D. A.; Klein, M. L.; McLendon, G. L.; Miller, J.
S.; Ratner, M. A.; Rossky, P. J.; Stupp, S. I.; Thompson, M.
E. Adv. Mater. 1998, 10, 1297.
2
6
-[2-(6-Dimethylaminobenzothiazol-2-yl)vinyl]benzothiazole-
-carbonitrile (12)
To a solution of 2-methylbenzothiazole-6-carbonitrile (11; 0.14 g,
.80 mmol) in MeOH (6 mL) was added 6-dimethylaminobenzothi-
(
4) Beckmann, S.; Etzbach, K. H.; Kramer, P.; Lukaszuk, K.;
Matschiner, R.; Schmidt, A.; Schuhmacher, P.; Sens, R.;
Seybold, G.; Würthner, F.; Wortmann, R. Adv. Mater. 1999,
0
azole-2-carbaldehyde (4; 0.16 g, 0.80 mmol) and solid NaOH (0.1
g, 2.5 mmol) as a base catalyst. The reaction mixture was stirred and
heated to reflux. After refluxing for 10 h, 2 mL of MeOH was evap-
orated and the resulting orange-red solid was collected by filtration,
washed and dried. The crude product was recrystallized from EtOH
to give 12 (0.20 g, 69%) as orange crystals; mp 277–279 °C.
11, 536.
(
(
(
5) Dalton, L. R.; Zhang, C.; Oh, M. C.; Zhang, H.; Steier, W.
H. Chem. Mater. 2001, 13, 3043.
6) Kanis, D. R.; Ratner, M. A.; Marks, T. J. Chem. Rev. 1994,
94, 195.
IR (CHCl ): 2220 cm– (C≡N).
1
1
3
7) Varanasi, P. R.; Jen, A. K. Y.; Chandrasekhar, J.;
Namboothiri, I. N. N.; Rathna, A. J. Am. Chem. Soc. 1996,
118, 12443.
H NMR (300 MHz, CDCl /TMS): d = 8.21 (d, 1 H, J = 1.7 Hz, H-
3
7
7
7
(
1
), 8.08 (d, 1 H, J = 9.3 Hz, H-4¢), 7.89 (d, 1 H, J = 8.8 Hz, H-4),
.83 (d, 1 H, J = 15.9 Hz, H ), 7.73 (dd, 1 H, J = 8.8, 1.7 Hz, H-5),
(8) Breitung, E. M.; Shu, C. F.; McMahon, J. R. J. Am. Chem.
Soc. 2000, 122, 1154.
(9) Brasselet, S.; Cherioux, F.; Audebert, P.; Zyss, J. Chem.
Mater. 1999, 11, 1915.
b
.58 (d, 1 H, J = 16.5 Hz, H ), 7.06 (d, 1 H, J = 2.2 Hz, H-7¢), 6.98
a
dd, 1 H, J = 9.3, 2.2 Hz, H-5¢); 3.09 [s, 6 H, N(CH ) ].
3
2
3
C NMR (75 MHz, CDCl /TMS): d = 169.67 (C-2), 158.70 (C),
3
(
(
(
10) Albert, I. D. L.; Morley, J. O.; Pugh, D. J. Phys. Chem. 1995,
1
(
1
(
56.49 (C), 149.82 (C), 146.00 (C), 138.16 (C), 135.44 (C), 132.87
99, 8024.
CH), 129.90 (CH), 126.53 (CH), 126.24 (CH), 124.27 (CH),
24.11 (CH), 118.88 (CN), 114.04 (CH), 109.13 (CCN), 102.25
CH), 41.01 [N(CH ) ].
11) Dirk, C. W.; Katz, H. E.; Schilling, M. L.; King, L. A. Chem.
Mater. 1990, 2, 700.
3
2
12) (a) Hrobárik, P.; Zahradník, P.; Fabian, W. M. Phys. Chem.
Chem. Phys. 2004, 6, 495. (b) Hrobárik, P. Diploma Thesis;
Comenius University: Bratislava, Czech Republic, 2004.
13) Miller, R. D.; Lee, V. Y.; Moylan, C. R. Chem. Mater. 1994,
3
–1
–1
UV (CHCl ): l = 468 nm (e = 29200 dm ·mol ·cm ).
3
max
Anal. Calcd for C H N S : C, 62.96; H, 3.89; N, 15.46; S, 17.69.
Found: C, 62.73; H, 3.89; N, 15.38; S, 17.34.
1
9
14
4 2
(
(
6
, 1023.
14) (a) Leng, W. N.; Zhou, Y.; Xu, Q. H.; Liu, J. Z. Polymer
001, 42, 9253. (b) Leng, W. N.; Zhou, Y.; Xu, Q. H.; Liu,
2
-[2-(4-Dimethylaminophenyl)vinyl]benzothiazole-6-carboni-
2
trile (13)
J. Z. Macromolecules 2001, 34, 4774.
To a solution of 2-methylbenzothiazole-6-carbonitrile (11; 0.14 g,
0
(
(
(
15) Mizuno, Y.; Adachi, K. J. J. Pharm. Soc. Jpn. 1952, 72, 739;
.80 mmol) in MeOH (6 mL) was added 4-dimethylaminobenzalde-
Chem. Abstr. 1954, 48, 2688g.
16) Giuamanini, G. A.; Chiavari, G.; Musiani, M. M.; Rossi, P.
Synthesis 1980, 743.
hyde (0.12 g, 0.80 mmol) and solid NaOH (0.1 g, 2.5 mmol) as
a base catalyst. The reaction mixture was stirred and heated to re-
flux. After refluxing for 12 h, 2 mL of MeOH was evaporated and
the resulting yellow-orange solid was collected by filtration,
washed and dried. The crude product was recrystallized from EtOH
to give 13 (0.18 g, 74%) as yellow-orange crystals; mp 215–217 °C.
17) Singh, H.; Rakesh, S.; Singh, K.; Contreras, R.; Uribe, G.
Tetrahedron 1989, 45, 5193.
(
(
18) Gilman, H.; Beel, J. A. J. Am. Chem. Soc. 1949, 71, 2328.
19) (a) Conte, M. Bull. Soc. Chim. Fr. 1967, 2834. (b) Borsche,
D. Liebigs Ann. Chem. 1939, 537, 53.
(20) (a) Vetelino, M. G.; Coe, J. W. Tetrahedron Lett. 1994, 35,
219. (b) Hamer, F. H. J. Chem. Soc. 1952, 3197.
(21) Jones, G.; Ollivierre, H.; Fuller, L. S.; Young, J.
Tetrahedron 1991, 47, 2851.
IR (CHCl ): 2210 cm– (C≡N).
1
1
3
H NMR (300 MHz, CDCl /TMS): d = 8.13 (d, 1 H, J = 1.6 Hz, H-
3
7
5
6
5
), 7.96 (d, 1 H, J = 8.5 Hz, H-4), 7.67 (dd, 1 H, J = 8.5, 1.6 Hz, H-
), 7.54 (d, 1 H, J = 15.9 Hz, H ), 7.49 (d, 2 H, J = 8.8 Hz, H-2¢,H-
b
¢), 7.18 (d, 1 H, J = 15.9 Hz, H ), 6.71 (d, 2 H, J = 8.8 Hz, H-3¢,H-
a
¢), 3.05 [s, 6 H, N(CH ) ].
(22) Stephens, F.; Wibberley, D. J. Chem. Soc. 1950, 3336.
3
2
1
3
(23) Dworczak, R.; Kieslinger, D. Phys. Chem. Chem. Phys.
C NMR (75 MHz, CDCl /TMS): d = 171.29 (C-2), 155.58 (C=N),
3
2
000, 2, 5057.
24) (a) Manning, W. B.; Horak, V. Synthesis 1978, 363.
b) Boggust, C. J. Chem. Soc. 1949, 355.
1
(
(
50.62 (C-4¢), 139.73 (CH ), 133.62 (CS), 128.43 (CH), 128.42
CH), 124.87 (CH), 121.74 (CH), 121.60 (C), 118.00 (CN), 114.98
CH), 110.96 (CH), 106.58 (CCN), 39.12 [N(CH ) ].
b
(
(
(
3
2
25) (a) Levkoev, I. I.; Sveshnikov, N. N.; Gorbacheva, I. N.;
Barvyn, N. S.; Krasnova, T. V. Zh. Obshch. Khim. 1954, 24,
280; Chem. Abstr., 1955, 49, 4627i. (b) Schmidt, O. Chem.
Ber. 1906, 39, 2413.
3
–1
–1
UV (CHCl ): l = 428 nm (e = 26400 dm ·mol ·cm ).
3
max
Anal. Calcd for C H N S: C, 70.79; H, 4.95; N, 13.76; S, 10.50.
Found: C, 70.51; H, 4.93; N, 13,54; S, 10.23.
18
15
3
Synthesis 2005, No. 4, 600–604 © Thieme Stuttgart · New York