Reaction of Herz salts with malononitrile: A general route to (6H-1,2,3-benzodithiazol-6-ylidene)malononitriles

Article abstract of DOI:10.1039/b110024f

6-Chloro-1,2,3-benzodithiazolium chlorides 1 (Herz salts) react with malononitrile to afford the highly coloured ylidenes 2 in low to moderate yields. The reaction is general but complex and in the case of the 6-chloro-4-methoxy-1,2,3-benzodithiazolium ch

Full text of DOI:10.1039/b110024f

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Reaction of Herz salts with malononitrile: a general route to
(6H-1,2,3-benzodithiazol-6-ylidene)malononitriles
Panayiotis A. Koutentisa and Charles W. Reesb
1
a Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus.
E-mail: koutenti@ucy.ac.cy
b Department of Chemistry, Imperial College of Science, Technology and Medicine, London,
UK SW7 2AY. E-mail: c.rees@ic.ac.uk
Received (in Cambridge, UK) 2nd November 2001, Accepted 3rd December 2001
First published as an Advance Article on the web 3rd January 2002
6-Chloro-1,2,3-benzodithiazolium chlorides 1 (Herz salts) react with malononitrile to afford the highly coloured
ylidenes 2 in low to moderate yields. The reaction is general but complex and in the case of the 6-chloro-4-methoxy-
1,2,3-benzodithiazolium chloride 1e the by-products 6-chloro-4-methoxy-1,3-benzothiazole-2-carbonitrile 3,
6-chloro-4-methoxy-2,3-dihydro-1,3-benzothiazole-2,2-dicarbonitrile 4, and 4-methoxy-6-thiocyanato-1,3-
benzothiazole-2-carbonitrile 5 were also isolated.
The term “Herz reaction” describes the condensation of aro-
matic amines and disulfur dichloride to give the corresponding
1,2,3-benzodithiazolium chlorides (Herz salts) and their sub-
sequent hydrolysis to afford 2-aminobenzenethiols.1,2 This
transformation and the accompanying para-chlorination of the
starting aniline have received considerable attention.3,4 How-
ever, although 1,2,3-benzodithiazolium salts have been known
for 80 years5 their chemistry that does not involve degradation
of the heterocyclic ring is still surprisingly sparse.
Recently we needed an independent synthesis of (5H-
naphtho[1,2-d][1,2,3]dithiazol-5-ylidene)malononitrile 2i and
were able to prepare it from 1-aminonaphthalene, which gave 5-
chloronaphtho[1,2-d][1,2,3]dithiazolium chloride when treated
with disulfur dichloride; when this Herz compound was treated
with malononitrile and 2 equivalents of base it gave the desired
target in moderate yield.6
pure samples. The naphtho- and the 1,2,5-benzothiadiaza Herz
salts gave the best yields (40 and 30% respectively) and it is
presumed that the stability added by the fused aromatic ring is
the contributing factor.
Interestingly the reaction of 3-monosubstituted anilines with
S2Cl2 to form Herz salts was reported to result in cyclisation
exclusively para to that substituent.9 Whilst 3-methoxyaniline
followed this trend, the Herz salts 1c and 1d derived from
3-methylaniline gave a mixture of 5-methyl (2c) and the more
sterically demanding 7-methyl substituted ylidene (2d) upon
reaction with malononitrile and base (Scheme 1). The mixture
A review of the literature showed that few such condensa-
tions with Herz salts had been carried out and that all involved
the use of amines. Interestingly these nitrogen based condensa-
tion products were found to exhibit antiallergic activities.7 We
now show that the reaction of malononitrile with Herz salts 1
to give ylidenes 2 is general, although moderate to low yielding,
and we discuss the identification of other minor products of
mechanistic interest.
Results and discussion
The Herz compounds were prepared according to literature
procedures (cf. refs. 1 and 8) and were washed with DCM to
remove soluble impurities and in general were obtained free
(by LRMS) of sulfur impurities. Some Herz salts such as the 5-
nitro-, 4-chloro-6-methyl- and the 4-phenyl-benzodithiazolium
chlorides were either unobtainable or the quality of the salt was
so poor that it could not be used. The displacement reaction
with malononitrile was quite general and a range of ylidenes
was synthesised (Table 1); however, attempts to react diethyl
malonate with the Herz salts to generate the analogous ylidenes
were unsuccessful.
The reactions were complex (TLC) but the ylidenes could be
readily identified by their intense blue–lilac colour in solution;
any co-running by-products could be removed from the
chromatographed fraction containing the ylidene by one or two
recrystallisations from glacial acetic acid to afford analytically
Scheme 1 Reagents and conditons: (i) S2Cl2, CH3CO2H, 90 ЊC, 8 h;
(ii) CH2(CN)2 (1 equiv.), EtNiPr2 (2 equiv.), DCM, 20 ЊC, 1 h, 5%.
1
was inseparable but the H and 13C NMR data for the con-
densation products 2c and 2d confirmed their identity. The ratio
1
of 2c : 2d was 2 : 1 (by H NMR) after recrystallisation from
glacial acetic acid.
In the solid state the ylidenes 2 were lustrous and metallic in
appearance. In solution the compounds were deep blue or lilac
in colour, with the lowest energy UV absorption band as high as
λmax 575 nm (log ε 4.35). This transition shifts further into
the red with increasing solvent polarity which suggests intra-
molecular charge transfer. The 13C NMR data of ylidenes 2
DOI: 10.1039/b110024f
J. Chem. Soc., Perkin Trans. 1, 2002, 315–319
This journal is © The Royal Society of Chemistry 2002
315

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Table 1 Ylidenes 2 derived from Herz salts 1 by treatment with malononitrile in the presence of Hünig’s base
Ylidene
R4
R5
R7
UV–vis λmax/nm (log ε)
13C (ppm) C(CN)2
Yield (%)
2a
2b
2c
2d
2e
2f
H
Me
H
H
MeO
H
H
H
Me
H
H
MeO
Me
H
H
H
H
Me
H
H
H
Me
H
H
575 (4.35)
569 (4.37)
N.d.b
61.2
60.8
61.5
62.8
60.2
59.7
61.3
62.2
61.3
63.3
11
16
5a
5a
11
14
13
15
40
30
N.d.b
564 (4.33)
554 (4.41)
569 (4.34)
569 (4.34)
530 (4.41)
517 (4.35)
2g
2h
2i
Me
Me
–CH᎐CH–CH᎐CH–
᎐
᎐
᎐
᎐
2j
᎐N–S–N᎐
a The 5- and 7-methyl derivatives 2c and 2d were obtained as an inseparable mixture from 3-methylaniline. b N.d. = not determined.
indicated that a considerable negative charge was located on
the central carbon of the malononitrile group [60–63 ppm,
C(CN)2] indicating the presence of a considerable push–pull
effect, the ‘push’ originating presumably from both sulfurs in
the dithiazole ring.
Despite attempts to optimise conditions for the treatment of
the Herz salts with malononitrile to give the ylidenes, the yields
were poor; variables investigated were reaction time, rate of
addition of base, quantity of base, order of addition, reaction
solvent (DCM, THF, EtOH) and base (Hünig’s base, pyridine,
DBU). The only factor that significantly affected the yields
of the ylidenes 2 was the quantity of base. If less base was
added the yield dropped; a 2 : 1 stoichiometry of base to
malononitrile was optimal.
The other products formed during the ylidene synthesis from
4-methoxy-1,2,3-benzodithiazolium chloride 1e and malono-
nitrile in the presence of Hünig’s base were investigated. Apart
from the ylidene 2e (11%), three other compounds were
isolated. A fluorescent cream coloured solid was identified
as 6-chloro-4-methoxybenzothiazole-2-carbonitrile 3 (24%); a
1H–13C correlation 13C NMR eliminated the possibility of the
isomeric benzisothiazole structure. A trace amount of a faint
yellow crystalline compound 4 was isolated and tentatively
assigned the dicyanomethylene structure, based on the LRMS
and on the fact that it readily formed the benzothiazole 3 on
standing. The remaining compound was tentatively assigned as
4-methoxy-6-thiocyanatobenzothiazole-2-carbonitrile 5 (5%).
All the standard spectral data were collected for the com-
pound 5 which is isomeric with the ylidene 2e, C10H5N3OS2, as
shown by microanalysis and HRMS. However compound 5 is
almost colourless and does not show the typical ylidene absorp-
tions in the UV spectrum; its spectrum λmax 303 (log ε 4.06) and
344 nm (3.84) was very similar to that of the benzothiazole 3
λmax 302 (log ε 4.17) and 339 nm (3.78), and both compounds
were strongly fluorescent. The LRMS of compound 5 had a
relatively intense fragmentation from the parent ion m/z (EI)
247 (62%) to 218 (100) which was significantly absent in the
LRMS of the ylidene 2e. LSMS confirmed the fragment
m/z (EI) 218 (100%) to come directly from the parent ion. A
similar fragmentation was seen from the benzothiazole 3 parent
ion m/z (EI) 224 (54%) to 195 (100). HRMS supported the
formula of CHO for this fragment. The IR data show two very
different nitrile stretches for 5 at 2231 and 2159 cmϪ1 and the
low wavenumber nitrile stretch is in the region for thiocyanates
(2170–2135 cmϪ1).10 The 13C NMR shows ten separate carbon
environments, two of which can be identified as belonging to
the two nitriles (112.9 and 109.7 ppm) and one of which is
the methoxy carbon resonance (57.3 ppm). The 1H NMR shows
the same aromatic substitution pattern as for the benzothiazole
1
3 and the ylidene 2e. Like the UV data, the 13C and H NMR
patterns for the aromatic resonances were closer to the benzo-
thiazole 3 than to the ylidene 2e. Based on all this we have
assigned the compound as the 6-thiocyanato derivative 5.
A suspicion that 6-chloro-4-methoxy-1,2,3-benzodithiazole
2-oxide 6 (formed by hydrolysis of the corresponding Herz salt
1e) was the species reacting with the malononitrile to give the
by-products 3, 4 and 5 was eliminated by treating a pure sample
of oxide 6 with malononitrile and Hünig’s base. TLC analysis
was unable to locate any of the above products.
Benzothiazoles have been prepared from Herz salts
previously; however, the procedure involved reduction of the
heterocyclic dithiazole ring to afford the aminobenzenethiol,
which is then cyclised to the benzothiazole.3 Since under our
reaction conditions such a reduction and cyclisation are not
feasible an alternative pathway must be operating.
We postulate (Scheme 2) that malononitrile attacks the
dithiazolium nitrogen† to afford the adduct 7 which ring opens
to the imine 8. Cyclisation by the highly nucleophilic sulfur
followed by proton transfer could yield benzothiazole 9 which
† Broadly similar, alternative, mechanisms initiated by nucleophilic
attack at either ring sulfur atom seem somewhat less likely, but cannot
be discounted at present.
316
J. Chem. Soc., Perkin Trans. 1, 2002, 315–319

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a Perkin-Elmer Lambda II spectrometer and inflections are
identified by the abbreviation ‘inf’. IR spectra were recorded on
a Perkin–Elmer 1710FT spectrometer and strong, medium and
weak peaks are represented by s, m and w respectively. 1H NMR
spectra were recorded on Bruker RX-400 (at 400 MHz) and
Bruker AM500 (at 500 MHz) machines. 13C NMR spectra were
recorded on Bruker RX-400 (at 100 MHz) and Bruker AM500
(at 125 MHz) machines. A doublet of sextets is represented
by dhex. Deuterated solvents were used for homonuclear lock
and the signals are referenced to the deuterated solvent peaks.
Mass spectra were recorded on a VG micromass 7070E or a
VG Autospec “Q” mass spectrometer. Microanalyses were
performed on a Perkin–Elmer 2400 CHN Analyser.
Reaction of Herz salts with malononitrile
Typical procedure. To a stirred suspension of 6-chloro-1,2,3-
benzodithiazol-2-ium chloride 1a11 (223 mg, 1 mmol) in DCM
(25 ml) at ca. 20 ЊC, malononitrile (66 mg, 1 mmol) was added
followed by the addition of Hünig’s base (348 µl, 2 mmol).
After 1 h TLC indicated a deep blue product and chroma-
tography (DCM) gave (6H-1,2,3-benzodithiazol-6-ylidene)-
propanedinitrile 2a (24 mg, 11%) as deep blue prisms, mp
283–285 ЊC (from glacial acetic acid) (Found: C, 49.7; H, 1.5;
N, 19.1. C9H3N3S2 requires C, 49.8; H, 1.4; N, 19.35%);
λmax(DCM)/nm 228 (log ε 3.66), 276 inf (3.96), 281 (3.99), 333
inf (4.00), 343 (4.12), 395 (3.23), 551 inf (4.33), 575 (4.35), 619
inf (4.13); νmax(Nujol)/cmϪ1 3096w, 3068w and 3047w (Ar CH),
2205s (CN), 2175m (CN), 1596s (C᎐N), 1513s (C᎐C), 1489s,
᎐
᎐
1455s, 1407s, 1353m, 1339m, 1245m, 1199w, 1171w, 1150m,
1029m, 985m, 902m, 870m, 838m, 789s, 725m, 649m; δH(400
MHz; DMSO-d6) 7.88 (1H, d, J 9.6 Hz, Ar H-4), 7.82 (1H, d,
J 2.0 Hz, Ar H-7), 7.50 (1H, dd, J 2.0, 9.6 Hz, Ar H-5); δC(100
MHz; DMSO-d6) 159.0, 153.2, 152.0, 129.0 (Ar CH), 128.2 (Ar
CH), 116.4 (CN), 116.4 (CN), 109.8 (Ar CH), 61.2 [C(CN)2];
m/z (EI) 217 (Mϩ, 100%), 190 (Mϩ Ϫ CHN, 5), 173 (4), 162 (12),
ϩ
ϩ
155 (4), 141 (9), 127 (5), 114 (5), 87 (3), 76 (C6H4 , 7), 64 (S2 , 9)
(Found: Mϩ, 216.9749. C9H3N3S2 requires M, 216.9768).
(4-Methyl-6H-1,2,3-benzodithiazol-6-ylidene)propanedinitrile
2b
Scheme 2
Similar treatment of 6-chloro-4-methyl-1,2,3-benzodithiazol-
2-ium chloride 1b11 with malononitrile and Hünig’s base gave
the title compound 2b (16%) as lustrous green–brown solid,
mp > 300 ЊC (from glacial acetic acid) (Found: C, 51.8; H, 2.2;
N, 18.0. C10H5N3S2 requires C, 51.95; H, 2.2; N, 18.2%);
λmax(DCM)/nm 228 (log ε 3.87), 275 inf (3.99), 279 (4.01), 347
(4.14), 395 (3.44), 414 (3.42), 545 inf (4.35), 569 (4.37), 610 inf
(4.16); νmax(Nujol)/cmϪ1 3068w (Ar CH), 2201s (CN), 1603s
could lose sulfur via a chain extension mechanism to give 4.
Alternatively loss of HCN from 9 could occur first to give 10
followed by loss of sulfur to afford benzothiazole 3. It is also
possible that cyanide could play a part in the desulfurisation
of 9 and 10 thus generating the thiocyanate anions which
could displace the activated chlorine atoms, particularly in the
starting Herz salt 1. This could presumably lead to the sub-
sequent formation of benzothiazole 5.
In conclusion we have demonstrated that the condensation
of malononitrile with Herz salts in the presence of base gives
highly coloured ylidenemalononitriles in low to modest yields
in somewhat complex reactions which can include direct attack
of the heterocyclic ring by malononitrile to give various benzo-
thiazole by-products.
(C᎐N), 1507s (C᎐C), 1432m, 1399s, 1319s, 1253w, 1133m,
᎐
᎐
1037w, 985m, 904m, 881w, 860w, 840w, 826w, 809m, 736m,
577w; δH(400 MHz; DMSO-d6) 7.70 (1H, d, J 2.0 Hz, Ar H ),
7.31 (1H, m, Ar H ), 2.53 (3H, d, J 1.1 Hz, CH3); δC(100 MHz;
DMSO-d6) 159.8, 153.2, 152.6, 138.4, 126.5 (Ar CH), 116.5
(CN), 116.5 (CN), 108.7 (Ar CH), 60.8 [C(CN)2], 18.8 (CH3);
m/z (EI) 231 (Mϩ, 100%), 203 (2), 198 (3), 171 (3), 140 (3), 128
(3), 115 (3), 101 (2), 89 (2), 64 (4) (Found: Mϩ, 230.9912.
C10H5N3S2 requires M, 230.9925).
Experimental
(5-Methyl-6H-1,2,3-benzodithiazol-6-ylidene)propanedinitrile 2c
and (7-methyl-6H-1,2,3-benzodithiazol-6-ylidene)-
propanedinitrile 2d
All reactions and column eluents were monitored by TLC using
commercial aluminium backed thin-layer chromatography
(TLC) plates (Merck Kieselgel 60 F254). The plates were
observed under UV light at 254 and 350 nm. The technique of
dry flash chromatography was used throughout for all non-
TLC scale chromatographic separations using Sorbsil C60 M40
silica. Petrol refers to light petroleum, bp 60–80 ЊC.
Melting points were determined using a Reichert Kofler
hot-stage apparatus. Solvents used for recrystallisation are indi-
cated after the melting point. UV spectra were obtained using
Similar treatment of a mixture of 6-chloro-5-methyl-1,2,3-
benzodithiazol-2-ium chloride 1c12 and 6-chloro-7-methyl-
1,2,3-benzodithiazol-2-ium chloride 1d with malononitrile and
Hünig’s base gave a mixture of the title compounds 2c and 2d
(5%) as blue needles, mp > 300 ЊC (from glacial acetic acid)
(Found: C, 52.05; H, 2.0; N, 18.0. C10H5N3S2 requires C, 51.95;
H, 2.2; N, 18.2%); δH(400 MHz; DMSO-d6) 2c: 7.82 (1H, s, Ar
J. Chem. Soc., Perkin Trans. 1, 2002, 315–319
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H-7), 7.72 (1H, m, Ar H-4), 2.56 (3H, d, J 0.8 Hz, 5-CH3); 2d:
7.79 (1H, d, J 9.7 Hz, Ar H-4), 7.55 (1H, d, J 9.7 Hz, Ar H-5),
2.60 (3H, s, 7-CH3); δC(100 MHz; DMSO-d6) 2c: 158.9, 151.5,
151.0, 138.4, 127.7 (Ar CH), 118.3 (CN), 117.8 (CN), 111.2
(Ar CH), 61.5 [C(CN)2], 21.6 (5-CH3); 2d: 158.0, 153.0, 149.2,
131.5 (Ar CH), 126.6 (ArCH), 119.0, 118.1 (CN), 117.6 (CN),
62.8 [C(CN)2], 22.4 (7-CH3); δC(100 MHz; DMSO-d6, DEPT
135) 2c: 127.7 (Ar CH), 111.2 (Ar CH), 21.6 (5-CH3); 2d: 131.5
(Ar CH), 126.6 (Ar CH), 22.4 (7-CH3); m/z (EI) 231 (Mϩ,
100%), 204 (Mϩ Ϫ CHN, 27), 177 [Mϩ Ϫ 2(CN), 3], 171 (3), 153
(CN), 118.2 (CN), 110.2 (Ar CH), 61.3 [C(CN)2], 17.5 (CH3),
16.4 (CH3); m/z (EI) 245 (Mϩ, 100%), 230 (Mϩ Ϫ CH3, 6), 218
(Mϩ Ϫ CHN, 29), 191 (4), 162 (9), 152 (6), 127 (4), 113 (6), 101
(2), 70 (3), 58 (9) (Found: Mϩ, 245.0089. C11H7N3S2 requires M,
245.0081).
(4,7-Dimethyl-6H-1,2,3-benzodithiazol-6-ylidene)propanedinitrile
2h
Similar treatment of 6-chloro-4,7-dimethyl-1,2,3-benzodi-
thiazol-2-ium chloride 1h with malononitrile and Hünig’s base
gave the title compound 2h (15 %) as lustrous green needles,
mp > 270 ЊC (from glacial acetic acid) (Found: C, 53.9; H, 2.7;
N, 17.1. C11H7N3S2 requires C, 53.9; H, 2.9; N, 17.1%);
λmax(DCM)/nm 229 (log ε 3.86), 276 (3.88), 318 (3.59), 353
(4.19), 408 (3.54), 427 inf (3.50), 545 inf (4.37), 569 (4.34),
ϩ
(9), 140 (3), 128 (3), 102 (4), 89 (2), 76 (2), 64 (S2 , 5) (Found:
Mϩ, 230.9936. C10H5N3S2 requires M, 230.9925).
(4-Methoxy-6H-1,2,3-benzodithiazol-6-ylidene)propanedinitrile
2e
606 inf (4.24); νmax(Nujol)/cmϪ1 2199s (CN), 1607s (C᎐N),
᎐
Similar treatment of 6-chloro-4-methoxy-1,2,3-benzodithiazol-
2-ium chloride 1e12 with malononitrile and Hünig’s base gave
the title compound 2e (11%) as green needles, mp > 300 ЊC
(from glacial acetic acid) (Found: C, 48.3; H, 2.0; N, 16.7.
C10H5N3OS2 requires C, 48.6; H, 2.0; N, 17.0%); λmax(DCM)/
nm 233 (log ε 3.92), 273 (3.91), 345 (4.05), 436 inf (3.66), 541 inf
(4.30), 564 (4.33), 610 inf (4.09); νmax(Nujol)/cmϪ1 3062w (Ar
1511s (C᎐C), 1493s, 1425s, 1405s, 1392s, 1355w, 1290m, 1214m,
᎐
1156w, 1122w, 1059m, 1033w, 962m, 909m, 896w, 880m, 834s,
741w, 722w, 685s, 654m; δH(400 MHz; DMSO-d6) 7.36 (1H, d,
J 1.2 Hz, Ar H-5), 2.57 (3H, s, CH3), 2.49 (3H, hidden by
DMSO, CH3); δC(100 MHz; DMSO-d6) 158.7, 153.0, 150.3,
136.6, 129.0 (Ar CH), 118.2 (CN), 117.7 (CN), 117.6, 62.2
[C(CN)2], 22.5 (CH3), 18.4 (CH3); m/z (EI) 245 (Mϩ, 100%),
230 (Mϩ Ϫ CH3, 8), 217 (Mϩ Ϫ CH2N, 20), 201 (3), 186 (5),
162 (17), 151 (10), 132 (10), 113 (10), 101 (5), 89 (8), 88 (7),
73 (21), 70 (18) (Found: Mϩ, 245.0071. C11H7N3S2 requires M,
245.0081).
CH), 2202s and 2183s (CN), 1607s (C᎐N), 1493s, 1461s, 1423s,
᎐
1368m, 1324s, 1266s, 1212m, 1190m, 1169s, 1146m, 1035s,
907m, 844s, 810m, 738s, 662m; δH(400 MHz; DMSO-d6) 7.32
(1H, d, J 1.6 Hz, Ar H ), 6.55 (1H, d, J 1.6 Hz, Ar H ), 3.99 (3H,
s, CH3O); δC(100 MHz; DMSO-d6) 155.1, 155.0, 153.2, 152.4,
116.6 (CN), 116.5 (CN), 106.0 (Ar CH), 102.5 (Ar CH), 60.2
[C(CN)2], 56.8 (CH3O); m/z (EI) 247 (Mϩ, 100%), 232 (Mϩ
Ϫ
(5H-Naphtho[1,2-d][1,2,3]dithiazol-5-ylidene)propanedinitrile
2i
CH3, 5), 214 (Mϩ Ϫ HS, 16), 204 (24), 186 (Mϩ Ϫ CHOS, 12),
ϩ
177 (9), 162 (5), 152 (3), 128 (4), 113 (7), 101 (3), 89 (6), 64 (S2 ,
Similar treatment of 5-chloronaphtho[1,2-d][1,2,3]dithiazol-2-
ium chloride 1i13 with malononitrile and Hünig’s base gave
the title compound 2i (40%) as lustrous green–brown needles,
mp 285–88 ЊC (from glacial acetic acid), identical with an
authentic sample.
8) (Found: Mϩ, 246.9879. C10H5N3OS2 requires M, 246.9874).
(5-Methoxy-6H-1,2,3-benzodithiazol-6-ylidene)propanedinitrile
2f
Similar treatment of 6-chloro-5-methoxy-1,2,3-benzodithiazol-
2-ium chloride 1f12 with malononitrile and Hünig’s base gave
the title compound 2f (14%) as green–brown needles, mp > 300
ЊC (from glacial acetic acid) (Found: C, 48.3; H, 1.9; N, 16.7.
C10H5N3OS2 requires C, 48.6; H, 2.0; N, 17.0%); λmax(DCM)/
nm 228 (log ε 4.08), 275 (3.93), 287 inf (3.80), 377 (3.90), 406 inf
(3.68), 536 inf (4.40), 554 (4.41), 599 inf (4.14); νmax(Nujol)/
(5H-[1,2,5]Thiadiazolo[3,4-e][1,2,3]benzodithiazol-5-ylidene)-
propanedinitrile 2j
Similar treatment of 5-chloro[1,2,5]thiadiazolo[3,4-e][1,2,3]-
benzodithiazol-2-ium chloride 1j with malononitrile and
Hünig’s base gave the title compound 2j (30%) as graphite grey
crystals, mp > 300 ЊC (from glacial acetic acid) (Found: C, 39.2;
H, 0.4; N, 25.4. C9HN5S3 requires C, 39.3; H, 0.4; N, 25.45%);
λmax(DCM)/nm 232 inf (log ε 3.69), 250 inf (3.86), 264 inf
(3.97), 277 (4.02), 291 (4.16), 297 (4.17), 302 (4.24), 341 (3.73),
357 (3.72), 378 (3.72), 493 inf (4.30), 517 (4.35), 555 inf (4.26),
590 inf (3.96); νmax(Nujol)/cmϪ1 3073w (Ar CH), 2209s (CN),
cmϪ1 3061w (Ar CH), 2201s and 2190s (CN), 1588m (C᎐N),
᎐
1515s, 1503s (C᎐C), 1454s, 1405s, 1363m, 1301w, 1260s, 1231s,
᎐
1181w, 1168w, 1048m, 1007s, 978w, 904w, 868s, 826s, 753m,
725s, 687w, 658w; δH(400 MHz; DMSO-d6) 7.81 (1H, s, Ar H ),
7.30 (1H, s, Ar H ), 3.94 (3H, s, CH3O); δC(100 MHz; DMSO-
d6) 160.0, 156.6, 149.4, 145.6, 117.5 (CN), 117.1 (CN), 109.6
(Ar CH), 102.4 (Ar CH), 59.7 [C(CN)2], 56.5 (CH3O); m/z (EI)
1549m and 1534m (C᎐N), 1519s (C᎐C), 1495m, 1394s, 1354w,
᎐
᎐
1332w, 1283s, 1212w, 1086m, 973w, 864w, 832m, 806w, 739m,
721w; δH(500 MHz; DMSO-d6) 7.95 (1H, s, Ar H ); δC(125
MHz; DMSO-d6) 156.8, 152.0, 151.2, 149.3, 144.5, 116.3 (CN),
116.2 (CN), 108.8 (Ar CH), 63.3 [C(CN)2]; m/z (EI) 275 (Mϩ,
100%), 217 (7), 191 (Mϩ Ϫ C2N2S, 2), 159 (Mϩ Ϫ C2N2S2, 3),
247 (Mϩ, 100%), 217 (Mϩ Ϫ CH2O, 36), 207 (25), 204 (Mϩ
Ϫ
C2H3O, 25), 192 (Mϩ Ϫ C2HNO, 44), 179 (41), 160 (14), 141
ϩ
(14), 113 (12), 89 (17), 64 (S2 , 17) (Found: Mϩ, 246.9891.
C10H5N3OS2 requires M, 246.9874).
137.5 (Mϩϩ, 3), 91 (8), 70 (5), 64 (S2 , 9), 46 (NSϩ, 3) (Found:
ϩ
(4,5-Dimethyl-6H-1,2,3-benzodithiazol-6-ylidene)propanedinitrile
Mϩ, 274.9411. C9HN5S3 requires M, 274.9394).
2g
Reaction of 6-chloro-4-methoxy-1,2,3-benzodithiazol-2-ium
chloride 1e with malononitrile and Hünig’s base
Similar treatment of 6-chloro-4,5-dimethyl-1,2,3-benzodi-
thiazol-2-ium chloride 1g with malononitrile and Hünig’s base
gave the title compound 2g (13 %) as lustrous green needles,
mp 259–266 ЊC (from glacial acetic acid) (Found: C, 54.0; H,
2.8; N, 17.0. C11H7N3S2 requires C, 53.9; H, 2.9; N, 17.1%);
λmax(DCM)/nm 228 (log ε 3.97), 280 (3.97), 359 (4.06), 406
(3.54), 428 inf (3.50), 552 inf (4.32), 569 (4.34), 610 inf (4.15);
To a stirred suspension of 6-chloro-4-methoxy-1,2,3-benzodi-
thiazol-2-ium chloride 1e (506 mg, 2 mmol) in DCM (25 ml) at
ca. 20 ЊC, malononitrile (132 mg, 2 mmol) was added followed
by the addition of Hünig’s base (695 µl, 4 mmol). After 12 h
TLC indicated several products; the volatiles were removed
and chromatography (petrol–DCM, 1 : 1) of the residue gave 6-
chloro-4-methoxybenzothiazole-2-carbonitrile 3 (108 mg, 24%)
as cream coloured needles, mp 126–128 ЊC (from cyclohexane)
(Found: C, 48.2; H, 2.4; N, 12.3. C9H5ClN2OS requires C, 48.2;
H, 2.2; N, 12.5%); λmax(DCM)/nm 256 (log ε 4.24), 294 inf
νmax(Nujol)/cmϪ1 3089w (Ar CH), 2200s (CN), 1577s (C᎐N),
1504s (C᎐C), 1396m, 1334s, 1196m, 1165s, 1128w, 1103w, 952w,
913w, 868w, 830m, 743m, 714w, 663m; δH(400 MHz; DMSO-d6)
7.76 (1H, s, Ar H-7), 2.52 (3H, s, CH3), 2.48 (3H, s, CH3);
δC(125 MHz; DMSO-d6) 159.6, 152.5, 150.3, 135.2, 134.2, 118.6
᎐
᎐
318
J. Chem. Soc., Perkin Trans. 1, 2002, 315–319

View Article Online
(4.11), 302 (4.17), 339 (3.78), 351 inf (3.71); νmax(Nujol)/cmϪ1
HCN, 49), 195 (Mϩ Ϫ HCN, –CHO, 100), 189 (Mϩ Ϫ HCN,
3070m and 3035w (Ar CH), 2228m (CN), 1585s and 1562s
–Cl, 6), 181 (15), 159 (26), 129 (9), 93 (12), 85 (30), 79 (13), 71
(C᎐N) or (C᎐C), 1464s, 1424s, 1386s, 1325s, 1270s, 1187w,
(52), 62 (7).
᎐
᎐
1137s, 1097m, 1036s, 908w, 863m, 841s, 794m, 783m, 749w,
640w, 603m; δH(400 MHz; DMSO-d6) 7.86 (1H, d, J 1.8 Hz, Ar
H ), 7.16 (1H, d, J 1.8 Hz, Ar H ), 3.98 (3H, s, CH3O); δC(100
MHz; DMSO-d6) 154.1, 141.1, 137.9, 135.4, 134.7, 113.7 (Ar
CH), 113.7 (CN), 109.5 (Ar CH), 56.6 (CH3O); δC(100 MHz;
DMSO-d6) 154.1 (dhex, J 1.5, 4.3, 6.0 Hz, C-4), 141.1 (t, J 6.8
Hz, C-3a), 137.9 (d, J 1.7 Hz, C-7a), 135.4 (s, C-2), 134.7 (t,
J 4.3 Hz, C-6), 113.7 (dd, J 5.3, 176.7 Hz, C-5 or C-7), 113.2 (s,
CN), 109.5 (dd, J 5.6, 167.1 Hz, C-5 or C-7), 56.6 (q, J 146 Hz,
CH3O); m/z (EI) 224 (Mϩ, 54%), 195 (Mϩ Ϫ CHO, 100), 189
(Mϩ Ϫ Cl, 7), 181 (16), 159 (27), 129 (10), 93 (13), 81 (9), 79
(15), 69 (27), 62 (9). Further elution (petrol–DCM, 1 : 3) gave
4-methoxy-6-thiocyanatobenzothiazole-2-carbonitrile 5 (24 mg,
5%) cream coloured needles, mp 169–172 ЊC (from cyclo-
hexane–pentane) (Found: C, 48.3; H, 2.0; N, 16.9. C10H5N3OS2
requires C, 48.6; H, 2.0; N, 17.0%); λmax(DCM)/nm 303 (log
ε 4.06), 344 (3.84); νmax(Nujol)/cmϪ1 3082w and 3062w (Ar CH),
Acknowledgements
We thank the EPSRC for a Research Studentship (P.A.K.),
Mr R. Sheppard for expert help with NMR spectroscopy,
MDL Information Sytems (UK) Ltd for financial support and
the Wolfson Foundation for establishing the Wolfson Centre
for Organic Chemistry in Medical Science at Imperial College.
References
1 W. K. Warburton, Chem. Rev., 1957, 57, 1011.
2 S. W. Schneller, Int. J. Sulfur Chem., 1976, 8, 579.
3 L. D. Huestis, M. L. Walsh and N. Hahn, J. Org. Chem., 1965, 30,
2763.
4 P. Hope and L. A. Wiles, J. Chem. Soc. (C), 1967, 1642.
5 L. Cassella and Co., GP. 360,690/1922 (R. Herz, Chem. Zentralbl.,
1922, 4, 948).
2231m (CN) and 2159m (SCN), 1620m and 1586s (C᎐N), 1565s
᎐
6 P. A. Koutentis and C. W. Rees, J. Chem. Soc., Perkin Trans. 1, 1999,
111.
and 1508m (C᎐C), 1383s, 1327s, 1308m, 1280s, 1270m, 1240m,
᎐
1209w, 1146m, 1108w, 1092w, 1041m, 906w, 892w, 848w, 830m,
771w, 744w, 721w; δH(400 MHz; DCM-d2) 7.75 (1H, d, J 1.6
Hz, Ar H ), 7.10 (1H, d, J 1.7 Hz, Ar H ), 4.10 (3H, s, CH3O);
δC(100 MHz; DCM-d2) 155.6, 143.7, 138.7, 136.7, 127.7, 114.6
(Ar CH), 112.9 (CN), 109.7 (SCN), 109.2 (Ar CH), 57.3
(CH3O); m/z (EI) 247 (Mϩ, 62%), 220 (Mϩ Ϫ CHN, 13), 218
(Mϩ Ϫ CH3N, 100), 204 (4), 191 (8), 159 (18), 149 (6), 107 (3),
94 (6), 69 (14) (Found: Mϩ, 246.9908. C10H5N3OS2 requires M,
246.9874); LSMS: (EI, B/E of m/z 247) 232 (2%), 218 (100), 204
(2), 191 (13), 159 (7); (EI, B2/E of m/z 218) 247 (Mϩ, 100%).
Further elution (DCM) gave (4-methoxy-6H-1,2,3-benzo-
dithiazol-6-ylidene)propanedinitrile 2e (54 mg, 11%) as green
needles, mp > 300 ЊC (from glacial acetic acid), identical to
that described above. A final elution (DCM) gave 6-chloro-4-
methoxy-2,3-dihydrobenzothiazole-2,2-dicarbonitrile 4 (6 mg,
1%) as faint yellow needles, m/z (EI) 251 (Mϩ, 3%), 224 (Mϩ Ϫ
7 E. Jacobi, R. Gericke and S. M. Coutts, EP: 0056475/1982 (Chem.
Abstr., 1982, 97, 216192).
8 L. Cassella and Co., BP 17 417/1914 (Chem. Abstr., 1922, 16, 500).
9 B. Kh. Strelets, L. S. Éfros and Z. V. Todres, Chem. Heterocycl.
Compd. (Engl. Transl.), 1970, 6, 327; B. Kh. Strelets, L. S. Éfros and
Z. V. Todres, Khim. Geterotsikl. Soedin., 1970, 6, 351 (Chem. Abstr.,
1970, 73, 66507).
10 E. Pretsch, J. Seibel, W. Simon and T. Clerc, Tables of Spectral Data
for Structure Determination of Organic Compounds, Springer-Verlag,
Berlin, 2nd Edition, 1989, p. I–65.
11 L. Cassella & Co., Ger. Pat. 367 345/1915 (Chem. Abstr., 1924, 18,
991).
12 B. Kh. Strelets, L. S. Éfros and Yu. I. Akulin, Chem. Heterocycl.
Compd. (Engl. Transl.), 1976, 12, 161; B. Kh. Strelets, L. S. Éfros
and Yu. I. Akulin, Khim. Geterotsikl. Soedin., 1976, 2, 183 (Chem.
Abstr., 1976, 85, 32925).
13 R. Shibata and M. Okuyama, Bull. Chem. Soc. Jpn., 1936, 11,
117.
J. Chem. Soc., Perkin Trans. 1, 2002, 315–319
319