Synthesis of Bis[1,2]dithiolo[1,4]thiazines and a [1,2]Dithiolo[1,4]thiazine from Tertiary Diisopropylamines

Article abstract of DOI:10.1021/jo9902345

The reaction of N-(2-chloroethyl)diisopropylamine 1a with S₂Cl₂ allows the selective one-pot preparation of the tricyclic 4-(2-chloroethyl) bisdithiolothiazines 2-4 or, by addition of phosphorus pentasulfide at a late stage in the re

Full text of DOI:10.1021/jo9902345

5010
J . Org. Chem. 1999, 64, 5010-5016
Syn th esis of Bis[1,2]d ith iolo[1,4]th ia zin es a n d a
[1,2]Dith iolo[1,4]th ia zin e fr om Ter tia r y Diisop r op yla m in es
Charles W. Rees,* Andrew J . P. White, and David J . Williams
Department of Chemistry, Imperial College of Science, Technology and Medicine,
London SW7 2AY, United Kingdom
Oleg A. Rakitin and Lidia S. Konstantinova
N. D. Zelinsky Institute of Organic Chemistry, Academy of Sciences,
Leninsky Prospect 47, 117913 Moscow, Russia
Carlos F. Marcos
Departamento de Quı´mica Orga´nica, Escuela Polite´cnica, Universidad de Extremadura,
10071 Ca´ceres, Spain
Toma´s Torroba*
Departamento de Quı´mica, Facultad de Ciencias, Universidad de Burgos,
09001 Burgos, Spain
Received February 8, 1999
The reaction of N-(2-chloroethyl)diisopropylamine 1a with S2Cl2 allows the selective one-pot
preparation of the tricyclic 4-(2-chloroethyl) bisdithiolothiazines 2-4 or, by addition of phosphorus
pentasulfide at a late stage in the reaction, of the dithiolothiazine 5. The chloroethyl derivative 2
is also obtained from (2-diisopropylamino)ethanethiol 1b, or its disulfide 1c, with S2Cl2, in a rare
conversion of a thiol or disulfide into the corresponding chloro compound. Compounds 2 and 5 are
also obtained from N-(2-hydroxyethyl)diisopropylamine 1d , though in much lower yields. The
reaction of N-(2-phenylthioethyl) (1e) or N-(2-phthalimidoethyl)diisopropylamines 1f,g affords
bisdithiolothiazines 7, 8, 9, and 11 and the dithiolopyrrole 10. A coherent set of reaction pathways
for the formation of these products is proposed. X-ray crystallography shows that the bisdithio-
lothiazine ring system of 2 is folded out of planarity about the thiazine N-S vector, with the
N-chloroethyl group folded back over the thiazine ring with the chlorine atom lying above the
thiazine sulfur atom; the dithiolothiazine ring system of 5 has the thiazine ring in a “sofa”
conformation.
In tr od u ction
zodithiazolones.5 During this work we found that Hu¨nig’s
base, a simple saturated tertiary amine, is converted in
a one-pot reaction by S2Cl2 into the fully unsaturated
tricyclic bis[1,2]dithiolo[3,4-b:4′,3′-e][1,4]thiazine ring sys-
tem6 or, at a higher temperature, into the bis[1,2]dithiolo-
[4,3-b:3′,4′-d]pyrrole system7 by selective sulfur extrusion
from the thiazine. Only the isopropyl groups of Hu¨nig’s
base reacted with S2Cl2, the ethyl group being un-
changed.8 This led us to consider the reactivity of
functionalized ethyl groups, both to explore the scope of
the reaction and possibly to intercept proposed interme-
diates on the long reaction pathway, by cyclizations
involving the ethyl group substituents. In this way, we
discovered that N-(2-chloroethyl)diisopropylamine may
afford either 4-(2-chloroethyl)bisdithiolothiazines or, by
addition of phosphorus pentasulfide at a late stage of the
The chemistry of various sulfur heterocycles such as
thiophenes and 1,3-dithioles has been extensively studied
since the discovery of their superconductivity1 and optical
and electronic switching properties.2 Polysulfur-nitrogen
heterocycles could be even better candidates for such
behavior, if practical syntheses were available. We have
studied the reactions of cyclic oximes with disulfur
dichloride (sulfur monochloride), S2Cl2, in the presence
of N-ethyldiisopropylamine (Hu¨nig’s base), to produce
suitable materials for electronic or optical applications,
and have discovered a simple route to some heterocyclic
pseudoazulenes,3 that constitute a new family of liquid
crystalline materials,4 and a one-pot synthesis of ben-
(1) (a) Gar´ın, J . Adv. Heterocycl. Chem. 1995, 62, 249. Misaki, Y.;
Fujiwara, H.; Yamabe, T. J . Org. Chem. 1996, 61, 3650. (b) Otsubo,
T.; Aso, Y.; Takimiya, K. Adv. Mater. 1996, 8, 203. (c) Horiuchi, S.;
Yamochi, H.; Saito, G.; Sakaguchi, K.; Kusunoki, M. J . Am. Chem. Soc.
1996, 118, 8604. (d) Roncali, J . J . Mater. Chem. 1997, 7, 2307.
(2) (a) Tsivgoulis, G. M.; Lehn, J .-M. Angew. Chem. 1995, 107, 1188,
Angew. Chem, Int. Ed. Engl. 1995, 34, 1119. (b) Gilat, S. L.; Kawai, S.
H.; Lehn, J .-M. Chem. Eur. J . 1995, 1, 275. (c) Kawai, S. H.; Gilat, S.
L.; Ponsinet, R.; Lehn, J .-M.; Ibid. 1995, 1, 285. (d) Tsivgoulis, G. M.;
Lehn, J .-M. Ibid. 1996, 2, 1399. (e) Tsivgoulis, G. M.; Lehn, J .-M. Adv.
Mater. 1997, 9, 39.
(4) Barbera´, J .; Rakitin, O. A.; Ros, M. B.; Torroba, T. Angew. Chem.
1998, 110, 308; Angew. Chem., Int. Ed. 1998, 37, 296.
(5) Polo, C.; Ramos, V.; Torroba, T.; Rakitin, O. A.; Rees, C. W.
Tetrahedron 1998, 54, 223.
(6) Marcos, C. F.; Polo, C.; Rakitin, O. A.; Rees, C. W.; Torroba, T.
Angew. Chem. 1997, 109, 283. Angew. Chem, Int. Ed. Engl. 1997, 36,
281.
(7) Marcos, C. F.; Polo, C.; Rakitin, O. A.; Rees, C. W.; Torroba, T.
J . Chem. Soc., Chem. Commun. 1997, 879.
(8) Rees, C. W.; White, A. J . P.; Williams, D. J .; Rakitin, O. A.;
Marcos, C. F.; Polo, C.; Torroba, T. J . Org. Chem. 1998, 63, 2189.
(3) (a) Rakitin, O. A.; Rees, C. W.; Torroba, T. J . Chem. Soc., Chem.
Commun. 1996, 427. (b) Rakitin, O. A.; Rees, C. W.; Williams, D. J .;
Torroba, T. J . Org. Chem. 1996, 61, 9178.
10.1021/jo9902345 CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/24/1999

Synthesis of Bis[1,2]dithiolo[1,4]thiazines
J . Org. Chem., Vol. 64, No. 14, 1999 5011
Sch em e 1
F igu r e 1. The molecular structure of 2.
the symmetrical structure in addition to the chloroethyl
group, and the IR spectrum showed one carbonyl absorp-
tion at 1634 cm-1, all in agreement with the assigned
structure 4-(2-chloroethyl)bis[1,2]dithiolo[3,4-b:4′,3′-e]-
[1,4]thiazine-3,5-dione (2). The X-ray analysis of 2 shows
the molecule to have a scorpion-like conformation (Figure
1), and a pattern of bonding within the fused ring system
very similar to that observed for the N-ethyl analogue.8
In both structures the geometry at nitrogen is pyramidal
with N(4) lying 0.22 Å out of the plane of its substituents.
The principal differences between the two species are a
change in the fold angle about the N‚‚‚S vector in the
thiazine ring [25° here compared with 34° for the N-ethyl
analogue] and in the relative orientations of the C(9)-
C(10) bond with respect to the N‚‚‚S vector in the thiazine
ring; the S‚‚‚N-C-C molecular torsion angles are 39 and
-6° in the N-chloroethyl and N-ethyl species, respec-
tively. A consequence of this torsional relationship in the
N-chloroethyl compound, and a gauche relationship about
the C(9)-C(10) bond, is a directing of the chlorine atom
over the center of the thiazine ring, the nonbonded
Cl‚‚‚S(8) distance being 3.85 Å.
An inspection of the packing of the molecules reveals
the formation of head-to-tail chains of molecules linked
via pairs of O‚‚‚S interactions (3.10 and 3.19 Å, Figure
2). Adjacent chains in one direction are oriented parallel
and coplanar to each other to form sheets. Centrosym-
metrically related pairs of sheets are arranged such that
the chlorine atoms of molecules within one sheet are
directed to lie approximately centrally between the sulfur
atoms of the dithiole rings of adjacent chains of the next
and vice versa thereby stabilizing the sheet structure via
Cl‚‚‚S cross-linking interactions (a -d in Figure 2).
The geometry of 2 has been optimized using ab initio
density functional theory methods,11 and the results are
in agreement with those from the crystallographic analy-
sis. Thus, there seems to be an attractive interaction
between the chlorine atom and the thiazine ring that
contributes to a crystal structure conformation which is
not purely a consequence of the crystal packing.
reaction, a new dithiolothiazine derivative.9 We have
made a systematic study of these reactions to understand
how the functionalization of the ethyl group in the
starting material, and the reaction conditions, affect the
nature of the final product. We now report precise
conditions for the selective synthesis of each class of
compounds, mechanistic proposals based on reaction
pathways, and the structures and crystal packing ob-
tained from X-ray diffraction analysis.
Resu lts a n d Discu ssion
Preliminary experiments had shown that electron-
withdrawing substituents in place of the ethyl group, as
in N,N-diisopropylacetamide or N,N-diisopropylcyana-
mide, suppressed the reaction of the isopropyl groups
with S2Cl2. We therefore selected the commercially avail-
able N-(2-chloroethyl)diisopropylamine 1a, which is readily
converted into the thiol 1b and its disulfide 1c,10 and
N-(2-hydroxyethyl)diisopropylamine 1d . These com-
pounds (1 equiv) were each treated with S2Cl2 (10 equiv)
and 1,4-diazabicyclo[2.2.2]octane (DABCO) (ca. 10 equiv)
in 1,2-dichloroethane for 3 days at room temperature.
Formic acid (20 equiv) was then added and the mixture
heated under reflux for 1 h, since we find that this
treatment gives clean reactions by converting the 3-chlo-
rodithiolium salt intermediates (e.g., 13) into dithiole-3-
ones. To our initial surprise, all four starting materials
1a -d gave exactly the same product 2, as yellow crystals
mp 175-177 °C (13-25%) after chromatography (Scheme
1). Mass spectrometry, HRMS, and microanalysis showed
2 to be a monochloro compound C8H4ClNO2S5; the 1H
NMR showed two vicinal methylene groups and 13C NMR
showed three unsaturated carbon signals consistent with
When the reaction of 1a (1 equiv) with S2Cl2 (1 equiv)
was performed in THF without addition of DABCO or
(9) Marcos, C. F.; Rakitin, O. A.; Rees, C. W.; Souvorova, L. I.;
Torroba, T.; White, A. J . P.; Williams, D. J . J . Chem. Soc., Chem.
Commun. 1998, 453.
(10) Davis, F. A.; Ray, J . K.; Kasperowicz, S.; Przeslawski, R. M.;
Durst, H. D. J . Org. Chem. 1992, 57, 2594.
(11) Rzepa, H.; Conesa, C. Electronic Conference on Heterocyclic
Chemistry ECHET 98, communication No. 004; for the complete
discussion see the web page http://www.ch.ic.ac.uk/ectoc/echet98/pub/
004/index.htm.

5012 J . Org. Chem., Vol. 64, No. 14, 1999
Rees et al.
F igu r e 2. Part of a pair of interlocking sheets of molecules
present in the structure of 2 showing the directing of the
chlorine atoms in one sheet into the plane of the other and
the associated Cl‚‚‚S and O‚‚‚S interactions (Å): (a) 3.48; (b)
3.36; (c) 3.53; (d) 3.44; (e) 3.10; (f) 3.19.
F igu r e 3. The molecular structure of 5 showing the near-
orthogonal relationship between the two dithiole rings and the
“sofa” conformation adopted by the thiazine ring.
Sch em e 2
mation is surprisingly rare for sulfur derivatives, but has
been achieved with sulfuryl chloride, followed by treat-
ment with triphenylphosphine.13
These results suggest that S2Cl2 reacted with the sulfur
groups faster than with isopropyl; otherwise the nucleo-
philic mercapto or hydroxy groups would probably have
reacted with some intermediate on the way to the
bisdithiolothiazine ring system. We therefore decided to
try to regenerate a thiol derivative from the chloro
compound by addition of a sulfur nucleophile at a late
stage in the reaction. Treatment of the 2-chloroethyl-
amine 1a (1 equiv) and S2Cl2 (1 equiv) in THF for 3 days
at room temperature was followed by addition of phos-
phorus pentasulfide (P4S10, 0.3 mol) with heating under
reflux for 5.5 h. Chromatography gave a new compound
5, C8H5NS7, as shiny orange needles, mp 240-241 °C
(40%)12 (Scheme 1). Treatment of the 2-hydroxyethyl-
amine 1d in the same conditions gave also 5, though in
much lower yield (7%). This compound 5 did not contain
chlorine though two different methylene groups were still
present, together with an aromatic methine group, in the
1H and 13C NMR spectra. The IR spectrum showed the
presence of thiocarbonyl but not a carbonyl group. The
presence of an aromatic proton indicated that the fully
fused tricyclic system of 2-4 had not been reached, and
suggested the presence of a 1,2-dithiole with one ring
hydrogen. The lack of either chlorine or mercapto groups
bonded to methylene indicated that the ethyl group could
be involved in a new ring. The structure 5,6-dihydro-4-
(3-thiono[1,2]dithiol-4-yl)[1,2]dithiolo[3,4-b][1,4]thiazine-
3-thione (5) was established by X-ray crystallography.
Compound 5 was found to have the partially saturated
structure illustrated in Figure 3. The thiazine ring has
a “sofa” conformation with C(5) lying 0.7 Å out of the
plane of the remaining five atoms (which are coplanar
to within 0.07 Å). The geometry at nitrogen is pyramidal,
N(4) being 0.28 Å out of the plane of its substituents.
The two dithiole rings are oriented approximately or-
thogonally (ca. 80°) thus minimizing interactions between
them. A comparison of the pattern of bonding in these
two rings shows that the C(3A)-C(7A) fusion between
one of them and the thiazine ring results only in changes
in the bond lengths of this bond [1.371(4) Å] and its
immediately adjacent neighbor C(7A)-S(1) [1.729(3) Å]
formic acid, the oxothione 3 was obtained as an orange
solid, mp 256-258 °C (10%),12 together with 2 (30%)12
(Scheme 2). Again the mass spectrum of 3 showed the
1
presence of a chlorine atom and the H NMR spectrum
two distinctive methylene groups. Desymmetrization of
the molecule by the thione group was shown by the
appearance of three new signals in the 13C NMR spec-
trum. IR also confirmed the presence of the thione and
ketone groups. Thus the unsymmetrical structure 4-(2-
chloroethyl)-3-oxobis[1,2]dithiolo[3,4-b:4′,3′-e][1,4]thiazine-
5-thione (3) was fully supported by all its spectroscopic
properties. Furthermore, the reaction can be performed
without the presence of oxygen donors by quenching the
3-chlorodithiolium salts with an additional base. Thus,
1a (1 equiv) was treated with S2Cl2 (10 equiv), DABCO
(5 equiv), and tetramethylammonium chloride (30 mg)
as a source of chloride anion, in chloroform for 3 days at
room temperature. Triethylamine (13 equiv) was then
added and the mixture stirred at room temperature for
an additional 3 h. By this extremely mild method, the
dithione 4 was obtained as a dark red solid, mp 229-
230 °C (14%). The new symmetrical structure 4-(2-
chloroethyl)bis[1,2]dithiolo[3,4-b:4′,3′-e][1,4]thiazine-3,5-
dithione (4) was fully supported by all its spectroscopic
properties.
In these reactions the chloroethylamine 1a , the mer-
captoethylamine 1b, the disulfide 1c, and the hydroxy-
ethylamine 1d have reacted with S2Cl2 in the same way
as Hu¨nig’s base itself, without detectable diversion of the
reaction pathway, but with the additional conversion at
some stage of the thiol, disulfide, and hydroxy groups into
the corresponding chloro compound. This last transfor-
(12) In the absence of DABCO, yields are calculated on the basis of
15 mol of amine 1a (or 1d ) giving 1 mol of product and 14 mol of amine
1a (or 1d ) hydrochloride.
(13) Still, I. W. J .; Kutney, G. W.; McLean, D. J . Org. Chem. 1982,
47, 560.

Synthesis of Bis[1,2]dithiolo[1,4]thiazines
J . Org. Chem., Vol. 64, No. 14, 1999 5013
Sch em e 3
F igu r e 4. Part of two overlapping sheets of molecules of 5
showing the intra and intersheet S‚‚‚S interactions. The S‚‚‚S
distances (Å) are (a) 3.31; (b) 3.45; (c) 3.52; (d) 3.55.
compared to those in the pendant ring system [1.348(4)
and 1.705(3) Å for C(8)-C(12) and C(12)-S(11) respec-
tively] which exhibit a higher degree of multiple bond
order.
The molecules pack to form sheets which are domi-
nated by short S‚‚‚S contacts [a , b, and d in Figure 4],
the S‚‚‚S distances ranging between 3.31 and 3.55 Å.
Adjacent sheets are offset such that the pendant dithiole
rings within one sheet insert into cavities formed between
groups of four molecules in a neighboring sheet, the
superstructure being stabilized via an additional S‚‚‚S
interaction [c in Figure 4] of 3.52 Å. These pendant
dithiole rings, although being oriented parallel to each
other, are offset, thereby precluding any π‚‚‚π interac-
tions between them.
The reaction of 2-chloroethylamine 1a , S2Cl2 and P2S5,
performed in the presence of DABCO, gave no stable
products. Dehydrogenation of 5 to the fully unsaturated
1,4-thiazine ring system by reaction with DDQ was
unsuccessful, giving only baseline material on TLC. This
was in contrast with the inertness of compound 2, in
which all attempts to displace the chlorine atom with
bases or iodide were unsuccessful. Treatment of 2 with
diisopropylamine for 7 h, or with sodium diisopropyla-
mide in diisopropylamine for 0.5 h, or with potassium
iodide in acetone for 5 h, gave unchanged 2. Compound
2 was also recovered after stirring with thiourea and
sodium hydroxide in water for 3 days, and it did not react
with phosphorus pentasulfide or Lawesson’s reagent in
refluxing THF for 50 h. On the other hand, compound 2
underwent thermal sulfur extrusion by refluxing in
chorobenzene for 7 days, affording quantitatively 4-(2-
chloroethyl)bis[1,2]dithiolo[4,3-b:3′,4′-d]pyrrole-3,5-di-
one (6), yellow crystals, mp 245-247 °C, fully character-
ized by spectroscopy. This slow sulfur extrusion from 2
contrasts with the fast sulfur extrusion from the N-ethyl
analogue which is complete in 3 h in refluxing xylene.8
This is probably due to the destabilization of the key
reaction intermediate, which requires electron release
from the nitrogen atom,8 by the inductive effect of the
chlorine atom.
groups into the starting material. Thus, reaction of N-(2-
phenylthioethyl)diisopropylamine 1e (1 equiv), obtained
from 1a and lithium thiophenoxide, with S2Cl2 (10 equiv)
and DABCO (6 equiv), in 1,2-dichloroethane for 3 days
at room temperature and then addition of formic acid (20
equiv) and heating the mixture for 45 min afforded
compound 7 as an orange solid, mp 148-149 °C (17%)
(Scheme 2). Mass spectrometry and microanalysis showed
1
7 to be C14H9NO2S6, and H and 13C NMR spectra showed
a phenyl ring and two vicinal methylene groups, sup-
porting the presence of the intact phenylthioethyl group
in a bisdithiolothiazine structure, and the carbonyl
groups were confirmed by IR, all in agreement with the
assigned structure 4-(2-phenylthioethyl)bis[1,2]dithiolo-
[3,4-b:4′,3′-e][1,4]thiazine-3,5-dione (7). The phenyl ring
was not chlorinated by S2Cl2. Furthermore, treatment of
N-(2-diisopropylaminoethyl)phthalimide14 (1f) (1 equiv),
readily obtained from 1a and potassium phthalimide in
dimethylformamide, with S2Cl2 (10 equiv) and DABCO
(10 equiv) in chloroform for 3 d at room temperature and
then addition of formic acid (20 equiv) and heating the
mixture under reflux for 1.5 h afforded compound 8,
orange crystals, mp 226-228 °C (25%) as the main
product (Scheme 3). Mass spectrometry and microanaly-
sis showed 8 to be C16H8N2O4S5, and the 1H NMR
spectrum showed the presence of two methylene groups
and four aromatic protons, indicating the presence of the
phthalimido group in 8 which was assigned the structure
4-(2-phthalimidoethyl)bis[1,2]dithiolo[3,4-b:4′,3′-e][1,4]-
thiazine-3,5-dione. Compound 8 was not obtainable by
the reaction of 2 and potassium phthalimide in DMF,
from which only baseline material (TLC) could be ob-
served. Treatment of 1f (1 equiv) with S2Cl2 (9 equiv) and
DABCO (9 equiv) in 1,2-dichloroethane for 3 days at room
temperature and heating the mixture under reflux for 1
h gave compound 9, black crystals, mp 245-247 °C (26%)
after chromatography, as the main product. All spectro-
Because of the inertness of the chlorine atom in the
primary alkyl chloride 2, in reactions with usual nucleo-
philes, we tried to obtain ethyl-substituted derivatives
of the tricyclic 1,4-thiazines by introducing suitable
(14) (a) Moore, R. J . Am. Chem. Soc. 1946, 68, 1657. (b) Chiti, S.
Farm. Ed. Sci. 1958, 13, 261 and 276.

5014 J . Org. Chem., Vol. 64, No. 14, 1999
Rees et al.
Sch em e 4
Sch em e 5
scopic data indicated for this compound 9 the structure
corresponding to the dithiono derivative of 8. In addition,
the reaction of 1f (1 equiv) with S2Cl2 (9 equiv) and
DABCO (9 equiv) in 1,2-dichlorobenzene for 3 days at
room temperature and heating the mixture under reflux
for 1.5 h afforded compound 10, black crystals, mp 291-
293 °C as the only product (63%). Mass spectrometry and
microanalysis showed 10 to be C16H8N2O2S6 and all
spectroscopic data indicated that 10 was the sulfur
extrusion product from 9, the 4-(2-phthalimidoethyl)bis-
[1,2]dithiolo[4,3-b:3′,4′-d]pyrrole-3,5-dithione (10). In a
similar way, treatment of N-(2-diisopropylaminoethyl)-
3,4,5,6-tetrachlorophthalimide (1g) (1 equiv), readily
obtained from 1a and sodium tetrachlorophthalimide in
dimethylformamide, with S2Cl2 (10 equiv) and DABCO
(5 equiv) in dichloroethane for 3 d at room temperature
and then addition of formic acid (20 equiv) and heating
the mixture under reflux for 45 min afforded compound
11, orange crystals, mp 238-240 °C (16%) (Scheme 4)
which was fully supported by spectroscopic and analytical
data.
the partially saturated thiazine 15, after further chlori-
nation. Salt 15 converts into the final product 5 by
reaction with more phosphorus pentasulfide. The com-
plete reaction scheme is probably quite complex and other
pathways can be envisaged. Thus, disalt 12 could react
with P4S10 to give the intermediate 16 which may cyclize
and be chlorinated to give 15. In some reactions of 1a (1
equiv) and S2Cl2 (1 equiv) in THF, a green mixture of
insoluble salts was filtered from the reaction mixture.
By treating this mixture with water or methanol, com-
pound 5 was isolated in very low yield (2-6%) after
column chromatography, showing that the conversion of
1a into 5 is a minor pathway even in the absence of P4S10.
Substitution of the chlorine atom in 1a by groups that
resist chlorination and are poorer leaving groups (such
as phenylthio or phthalimido) prevents the pathway to
5 and the reaction gives bis[1,2]dithiolo[1,4]thiazine
derivatives (such as 7 and 8) exclusively.
In contrast with the straightforward synthesis of
compounds 8-11, their inertness and low solubility in
common solvents made their chemistry difficult. Thus,
all attempts at deprotection of the amino group from
phthalimide derivatives 8-11 were unsuccessful. For
example, refluxing 10 and hydrazine hydrochloride in
ethanol for 24 h left 10 unchanged and the same reaction
in DMF for 8 h completely decomposed 10. Refluxing 10
and concentrated hydrochloric or hydrobromic acid in
aqueous dimethyl sulfoxide or aqueous chloroform left
10 unchanged. On the other hand, treatment of 11 with
hydrazine in refluxing ethanol for 4 h, or with ethylene-
diamine15 in refluxing acetonitrile for 5 h, gave only
intractable solids. Similar attempts at deprotecting 8 and
9 failed.
Con clu sion s
Rea ction Mech a n ism s. A plausible mechanism for
all the transformations of 1a (as the actual starting
material or as obtained in situ by chlorination of 1b-d )
could start by formation of an intermediate disalt 12 (cf.
ref 8) that may further react with S2Cl2 to form, after
extrusion of sulfur, the bis[1,2]dithiolo[1,4]thiazine disalt
13, which affords the dione 2 by reaction with formic acid
or, alternatively, a mixture of dione 2 and oxothione 3
by reaction with sulfur and oxygen donors present in the
reaction mixture (Scheme 5). Similarly, disalt 13 gives
dithione 4 by quenching with triethylamine. Further
extrusion of sulfur from 2 affords 6. In the presence of
phosphorus pentasulfide the disalt 12 could give the
intermediate 14 which could then cyclize as shown to give
Commercial N-(2-chloroethyl)diisopropylamine, and
related compounds, are shown to give some quite complex
1,4-thiazine derivatives, such as 2-5, in one-pot reactions
with disulfur dichloride. The products can be varied by
changing the reactant ratios and solvents, and by the
addition of amines, oxygen donors, or phosphorus pen-
tasulfide. The mild reaction conditions should allow the
ready elaboration of these structures to give compounds
of potential use as new electronic materials in the 1,2-
dithiole series,16 and in pharmaceutical research.17
(16) (a) Terzis, A.; Kamitsos, E. I.; Psycharis, V.; Zambounis, J . S.;
Swiatek, J .; Papavassiliou, G. C. Synth. Met. 1987, 19, 481. (b)
Fangha¨nel, E.; Richter, A. M.; Kordts, B.; Beye, N. Phosphorus, Sulfur
1989, 43, 165.
(17) Aimar, M. L.; Rossi, R. H. Tetrahedron Lett. 1996, 37, 2137,
and references therein.
(15) Debenham, J . S.; Fraser-Reid, B. J . Org. Chem. 1996, 61, 432.

Synthesis of Bis[1,2]dithiolo[1,4]thiazines
J . Org. Chem., Vol. 64, No. 14, 1999 5015
NOS6: C, 26.84; H, 1.13; N, 3.91. Found: C, 27.08; H, 0.91;
N, 3.81. Compound 2 (277 mg, 30%)12 was also obtained.
4-(2-Ch lor oe t h yl)b is[1,2]d it h iolo[3,4-b:4′,3′-e][1,4]-
th ia zin e-3,5-d ith ion e (4). Disulfur dichloride (4 mL, 50
mmol) was added dropwise to a solution of recently distilled
N-(2-chloroethyl)diisopropylamine (1a ) (0.82 g, 5 mmol), DAB-
CO (2.80 g, 25 mmol), and tetramethylammonium chloride (30
mg) in chloroform (100 mL) at -40 °C. The mixture was stirred
for 15 min at -40 °C and then for 3 days at room temperature.
Triethylamine (9.1 mL, 65 mmol) was then added and the
mixture stirred at room temperature for additional 3 h. The
reaction mixture was filtered through Celite, and the solvent
was removed in the rotary evaporator. MPLC (petroleum ether
to a mixture of petroleum ether/CH2Cl2 1:1) of the residue
afforded compound 4 as a dark red solid (petroleum ether/
Exp er im en ta l Section
Disulfur dichloride, DABCO, phosphorus pentasulfide,
lithium thiophenoxide, potassium phthalimide, and tetrachlo-
rophthalimide were purchased from Aldrich and used without
further purification. N-(2-Chloroethyl)diisopropylamine hy-
drochloride (Aldrich) was used as source of free amine. THF
was distilled from sodium. 1,2-Dichloroethane and chloroben-
zene were distilled from phosphorus pentoxide. Melting points
were determined using a Kofler hot-stage apparatus. CH2 and
CH groups were identified by DEPT experiments on repre-
sentative examples. Column chromatography (MPLC) was
carried out on a medium-pressure Gilson liquid chromatog-
raphy apparatus, with silica gel C60 (Merck). Petroleum ether
refers to the fraction bp 40-60 °C.
4-(2-Ch lor oe t h yl)b is[1,2]d it h iolo[3,4-b:4′,3′-e][1,4]-
th ia zin e-3,5-d ion e (2). Disulfur dichloride (4.0 mL, 50 mmol)
was added dropwise to a solution of recently distilled N-(2-
chloroethyl)diisopropylamine (1a ) (0.82 g, 5 mmol) [from
treatment of its hydrochloride with aqueous sodium hydroxide
at 0 °C, and extraction with ice-cold diethyl ether], or (2-
diisopropylamino)ethanethiol (1b)10 (0.81 g, 5 mmol), or bis-
[2-(diisopropylamino)ethyl]disulfide (1c)10 (0.80 g, 2.5 mmol)
or N-(2-hydroxyethyl)diisopropylamine (1d ) (0.73 g, 5 mmol)
and DABCO (5.0 g, 45 mmol, for 1a , and 4.5 g, 40 mmol, for
1b, 1c, and 1d ) in 1,2-dichloroethane (100 mL) at -40 °C. The
mixture was stirred for 15 min at -40 °C and then for 3 days
at room temperature. Formic acid (4 mL, 100 mmol) was then
added dropwise at 5 °C and the mixture refluxed for 1 h (for
1a ,b and 1d ) and 2 h (for 1c). The reaction mixture was filtered
through Celite, and the solvent was removed in the rotary
evaporator. MPLC (silica gel Merck 60, petroleum ether to
CH2Cl2) of the residue afforded 2 as yellow crystals (petroleum
ether/CH2Cl2) (427 mg, 25%) from 1a or 1b, (274 mg, 16%)
from 1c, and (222 mg, 13%) from 1d ; mp 175-177 °C. 1H NMR
(400 MHz, CDCl3) δH 3.73 (t, J 5.7, 2H, CH2), 4.23 (t, J 5.7,
2H, CH2); 13C NMR (100 MHz, CDCl3) δC 43.43 and 47.22 (2
× CH2), 136.62 and 146.68 (2 × sp2Ctertiary), 182.08 (CdO); IR
(CCl4, cm-1) νmax 1666 and 1634 (CdO), 1561, 1522; m/z (EI,
70 eV) 343 (M+ + 2, 30), 341 (M+, 51), 305 (M - 36, 44), 292
(M - 49, 67); HRMS, M+ ) 340.8537 C8H4ClNO2S5 required
340.8534. Anal. Calcd for C8H4ClNO2S5: C, 28.11; H, 1.18; N,
4.10. Found: C, 28.45; H, 0.90; N, 3.92.
1
CH2Cl2) (262 mg, 14%); mp 229-230 °C. H NMR (400 MHz,
pyridine-d5) δH 3.92 (t, J 6.1, 2H, CH2), 4.91 (t, J 6.1, 2H, CH2);
13C NMR (100 MHz, pyridine-d5) δC 43.74 and 48.83 (2 × CH2),
148.31 and 159.40 (2 × sp2Ctertiary), 203.24 (CdS); IR (CCl4,
cm-1) νmax 1490, 1452, 1312 (CdS); m/z (EI, 70 eV) 323 (M -
50, 12). Anal. Calcd for C8H4ClNS7: C, 25.69; H, 1.08; N, 3.75.
Found: C, 25.64; H, 1.12; N, 3.79.
5,6-Dih yd r o-4-(3-th ion o[1,2]d ith iol-4-yl)-[1,2]d ith iolo-
[3,4-b][1,4]th ia zin e-3-th ion e (5). Disulfur dichloride (2.86
mL, 35 mmol) was added dropwise to a solution of recently
distilled N-(2-chloroethyl)diisopropylamine (1a ) (5.73 g, 35
mmol) or N-(2-hydroxyethyl)diisopropylamine (1d ) (5.65 g, 35
mmol) in THF (50 mL) at -40 °C. The mixture was stirred
for 15 min at -40 °C and then for 3 days at room temperature.
Phosphorus pentasulfide (4.45 g, 10 mmol) was then added
and the mixture refluxed for 5.5 h. The reaction mixture was
filtered through Celite, and the solvent was removed in the
rotary evaporator. MPLC (petroleum ether to CH2Cl2) of the
residue afforded
5 as orange needles (petroleum ether/
CH2Cl2) (317 mg, 40%)12 from 1a and (56 mg, 7%)12 from 1d ;
mp 240-241 °C. 1H NMR (400 MHz, pyridine-d5) δH 3.01 (t, J
4.7, 2H, CH2), 4.05 (m, br, 2H, CH2), 7.72 (s, 1H, CdCH); 13C
NMR (100 MHz, pyridine-d5) δC 23.13 and 47.31 (2 × CH2 from
DEPT), 142.40 (sp2CH from DEPT), 144.80, 153.25 and 157.20
(3 × sp2Ctertiary), 203.60 and 210.80 (2 × CdS); IR (CCl4, cm-1
)
νmax 1460, 1345 and 1317 (CdS), 1242; m/z (EI, 70 eV) 339
(M+, 46), 306 (M - 33, 19), 275 (M - 64, 96); HRMS, M+
)
338.8466 C8H5NS7 required 338.8467. Anal. Calcd for
C8H5NS7: C, 28.30; H, 1.48; N, 4.13. Found: C, 28.16; H, 1.58;
N, 3.95. Crystal data for compound 5 have already been
deposited; CCDC 182/736.
Cr ysta l d a ta for 2: C8H4NO2S5Cl, M ) 341.9, triclinic, P1h
(no. 2), a ) 7.064(1), b ) 8.320(1), c ) 11.427(1) Å, R ) 76.77-
(1), â ) 73.45(1), γ ) 66.53(1)°, V ) 585.5(1) Å3, Z ) 2, Dc )
1.939 g cm-3, µ(Mo-KR) ) 12.0 cm-1, F(000) ) 344. An orange
block of dimensions 0.93 × 0.90 × 0.60 mm was used. 11832
Independent reflections were measured at 153 K on a Siemens
P4/PC diffractometer with Mo-KR radiation (λ ) 0.71073 Å)
using ω-scans. The structure was solved by direct methods and
all of the non-hydrogen atoms were refined anisotropically
using full matrix least-squares based on F2 with absorption
corrected data (Gaussian, max. and min transmission factors
0.53 and 0.38, respectively) to give R1 ) 0.039, wR2 ) 0.102
for 9303 independent observed reflections [|Fo| > 4σ(|Fo|), 2θ
e 98°] and 155 parameters; CCDC 126155.
4-(2-Ch lor oeth yl)bis[1,2]d ith iolo[4,3-b:3′,4′-d ]p yr r ole-
3,5-d ion e (6). Compound 2 (100 mg, 0.3 mmol) was heated at
reflux in chlorobenzene (60 mL) for 7 days, affording 6 as
yellow crystals (petroleum ether/CH2Cl2) (90 mg, 99%); mp
1
245-247 °C. H NMR (400 MHz, CDCl3) δH 3.78 (t, J 5.8, 2H,
CH2), 4.82 (t, J 5.8, 2H, CH2); 13C NMR (100 MHz, pyridine-
d5) δC 44.08 and 44.79 (2 × CH2), 131.95 and 135.99 (2 ×
sp2Ctertiary), 182.35 (CdO); IR (KBr, cm-1) νmax 1639 and 1624
(CdO), 1339; m/z (EI, 70 eV) 311 (M+ + 2, 49), 309 (M+, 100),
273 (M - 36, 27), 260 (M - 49, 72); HRMS, M+ ) 308.8809
C8H4ClNO2S4 required 308.8813. Anal. Calcd. for
C8H4ClNO2S4: C, 32.49; H, 1.35; N, 4.74. Found: C, 32.36; H,
1.62; N, 4.56.
4-(2-Ch lor oeth yl)-3-oxobis[1,2]d ith iolo[3,4-b:4′,3′-e][1,4]-
th ia zin e-5-th ion e (3). Disulfur dichloride (3.3 mL, 40 mmol)
was added dropwise to a solution of recently distilled N-(2-
chloroethyl)diisopropylamine (1a ) (6.65 g, 40 mmol), in THF
(50 mL) at -40 °C. The mixture was stirred for 15 min at -40
°C and then for 3 days at room temperature and then refluxed
for 2.5 h. The reaction mixture was filtered through Celite,
and the solvent was removed in the rotary evaporator. MPLC
(petroleum ether to CH2Cl2) of the residue afforded compound
3 as orange crystals (petroleum ether/CH2Cl2) (96 mg, 10%);12
4-(2-P h en ylth ioeth yl)bis[1,2]d ith iolo[3,4-b:4′,3′-e][1,4]-
th ia zin e-3,5-d ion e (7). Lithium thiophenoxide, 1.0 M solution
in THF (12 mL, 12 mmol), was added dropwise to a solution
of recently distilled N-(2-chloroethyl)diisopropylamine (1a )
(1.97 g, 12 mmol) in THF (22 mL), and the mixture was stirred
for 2 days at room temperature, affording N-(2-phenylthioeth-
yl)diisopropylamine (1e) as a liquid (2.57 g, 90%), m/z (EI, 70
eV) 238 (M+ + 1, 20). Disulfur dichloride (4 mL, 50 mmol) was
added dropwise to a solution of N-(2-phenylthioethyl)diiso-
propylamine (1e) (1.19 g, 5 mmol), DABCO (3.37 g, 30 mmol),
and tetramethylammonium chloride (30 mg) in 1,2-dichloro-
ethane (100 mL) at -40 °C. The mixture was stirred for 15
min at -40 °C and then for 3 days at room temperature.
Formic acid (4 mL, 100 mmol) was then added dropwise at 5
°C and the mixture refluxed for 45 min. The reaction mixture
was filtered through Celite, and the solvent was removed in
1
mp 256-258 °C. H NMR (400 MHz, CDCl3) δH 3.71 (t, J 5.7,
2H, CH2), 4.43 (m, br, 2H, CH2); 13C NMR (100 MHz, CDCl3)
δC 43.19 and 47.66 (2 × CH2), 137.08, 147.74, 148.42 and
155.75 (4 × sp2Ctertiary), 182.18 (CdO), 200.90 (CdS); IR (CCl4,
cm-1) νmax 1657 and 1637 (CdO), 1552, 1479, 1285 (CdS); m/z
(EI, 70 eV) 359 (M+ + 2, 21), 357 (M+, 35), 322 (M - 35, 14),
308 (M - 49, 10), 295 (M - 62, 27); HRMS, M+ ) 356.8387
C8H4ClNOS6 required 356.8306. Anal. Calcd for C8H4Cl-

5016 J . Org. Chem., Vol. 64, No. 14, 1999
Rees et al.
the rotary evaporator. MPLC (petroleum ether to CH2Cl2) of
CH2Cl2) (1.04 g, 63%); mp 291-293 °C. 1H NMR (400 MHz,
pyridine-d5) δH 4.37 (t, J 4.8, 2H, CH2), 5.93 (t, J 4.8, 2H, CH2),
7.49 (q, J a-b 5.3, J a-c 3.0, 2H, Ph), 7.76 (q, J b-a 5.3, J b-d 3.0,
2H, Ph); 13C NMR (100 MHz, pyridine-d5) δC 40.34 and 41.58
(2 × CH2, from DEPT), 124.76 and 135.74 (2 × CHaromatic, from
DEPT), 134.16, 139.25 and 147.49 (3 × sp2Ctertiary), 169.68
(CdO), 201.48 (CdS); IR (CCl4, cm-1) νmax 1763 and 1702
(CdO), 1430, 1346, 1275 (CdS); m/z (EI, 70 eV) 454 (M + 2,
31), 452 (M+, 100), 419 (M - 33, 18); HRMS, M+ ) 451.8931
the residue afforded 7 as an orange solid (petroleum ether/
1
CH2Cl2) (353 mg, 17%); mp 148-149 °C. H NMR (400 MHz,
CDCl3) δH 3.18 (t, J 6.4, 2H, CH2), 4.04 (t, J 6.4, 2H, CH2),
7.18-7.31 (m, 5H, Ph); 13C NMR (100 MHz, CDCl3) δC 34.04
and 44.37 (2 × CH2, from DEPT), 126.71, 129.10 and 129.88
(3 × CHaromatic, from DEPT), 134.82, 136.60 and 146.30 (3 ×
sp2Ctertiary), 181.96 (CdO); IR (CCl4, cm-1) νmax 1663 (CdO),
1559; m/z (EI, 70 eV) 415 (M+, 10), 305 (M - 110, 10), 278 (M
- 137, 11), 273 (M - 142, 20), 77 (100); HRMS, M+ ) 414.8934
C
16H8N2O2S6 requires 451.8910. Anal. Calcd for C16-
C
14H9NO2S6 requires 414.8958. Anal. Calcd. for C14H9NO2S6:
H8N2O2S6: C, 42.46; H, 1.78; N, 6.19. Found: C, 42.35; H, 1.84;
N, 6.04.
C, 40.46; H, 2.18; N, 3.37. Found: C, 40.47; H, 2.07; N, 3.23.
4-(2-P h th a lim id oeth yl)bis[1,2]d ith iolo[3,4-b:4′,3′-e][1,4]-
th ia zin e-3,5-d ion e (8). Disulfur dichloride (5.3 mL, 65 mmol)
was added dropwise to a solution of N-(2-diisopropylaminoeth-
yl)phthalimide14 (1f) (1.79 g, 6.5 mmol) and DABCO (7.31 g,
65 mmol) in absolute chloroform (100 mL) at -40 °C. The
mixture was stirred for 15 min at -40 °C and then for 3 days
at room temperature. Formic acid (5.2 mL, 130 mmol) was then
added dropwise at 5 °C and the mixture refluxed for 1.5 h.
The reaction mixture was filtered through Celite and the
solvent was removed in the rotary evaporator. MPLC (petro-
leum ether to CH2Cl2) of the residue afforded 8 as orange
crystals (petroleum ether/CH2Cl2) (736 mg, 25%); mp 226-
228 °C. 1H NMR (400 MHz, CDCl3) δH 3.96 (t, J 6.1, 2H, CH2),
4.33 (t, J 6.1, 2H, CH2), 7.74 (m, 2H, Ph), 7.84 (m, 2H, Ph);
13C NMR (100 MHz, CDCl3) δC 37.92 and 42.63 (2 × CH2),
123.34 and 134.15 (2 × CHaromatic), 131.97, 136.30 and 145.85
4-[2-(Tet r a ch lor op h t h a lim id o)et h yl]b is[1,2]d it h iolo-
[3,4-b:4′,3′-e][1,4]th ia zin e-3,5-d ion e (11). Sodium tetrachlo-
rophthalimide (3.07 g, 10 mmol) [obtained quantitatively from
tetrachlorophthalimide (2.85 g, 10 mmol) and sodium hydride
(0.26 g, 11 mmol) stirred in THF (50 mL) for 20 h at room
temperature] and N-(2-chloroethyl)diisopropylamine (1a ) (1.64
g, 10 mmol) were stirred in dimethylformamide (5 mL) for 18
h at room temperature. The residue afforded N-(2-diisopropyl-
aminoethyl)-3,4,5,6-tetrachlorophthalimide (1g) as a colorless
solid (CH2Cl2) (1.45 g, 35%); mp 92-94 °C. 1H NMR (400 MHz,
CDCl3) δH 0.96 (d, 12H, J 6.3, 4 × CH3), 2.65 (t, 2H, J 6.9,
CH2), 3.01 (q, 2H, J 6.3, 2 × CH), 3.68 (t, 2H, J 6.9, CH2); 13
C
NMR (100 MHz, CDCl3) δC 20.67, 39.55, 42.58, 48.48, 127.69,
129.46, 139.89, 163.59 (CdO); IR (CCl4, cm-1) νmax 2969, 1770
and 1712 (CdO), 1401; m/z (EI, 70 eV) 415 (7), 413 (16), 411
(15), 312 (92), 310 (89), 142 (100). Disulfur dichloride (2.0 mL,
25 mmol) was added dropwise to a solution of N-(2-diisopro-
pylaminoethyl)-3,4,5,6-tetrachlorophthalimide (1g) (1.03 g, 2.5
mmol), DABCO (1.40 g, 12.5 mmol) and tetramethylammo-
nium chloride (30 mg) in 1,2-dichloroethane (50 mL) at -40
°C. The mixture was stirred for 15 min at -40 °C, then for 3
days at room temperature. Formic acid (2 mL, 50 mmol) was
then added dropwise at 5 °C and the mixture refluxed for 45
min. The reaction mixture was filtered through Celite and the
solvent was removed in the rotary evaporator. MPLC (petro-
leum ether to CH2Cl2) of the residue afforded 11 as orange
crystals (petroleum ether/CH2Cl2) (236 mg, 16%); mp 238-
240 °C.1H NMR (400 MHz, CDCl3) δH 3.80 (t, J 6.8, 2H, CH2),
(3 × sp2Ctertiary), 168.10 and 181.73 (2 × CdO); IR (CCl4, cm-1
)
νmax 1772, 1710, and 1624 (CdO), 1559, 1519; m/z (EI, 70 eV)
452 (M+, 54), 420 (M - 32, 6), 337 (10), 305 (10), 292 (M -
160, 73), 174 (100); HRMS, M+ ) 451.9093 C16H8N2O4S5
requires 451.9088. Anal. Calcd for C16H8N2O4S5: C, 42.47; H,
1.78; N, 6.19. Found: C, 42.34; H, 1.91; N, 6.26.
4-(2-P h th a lim id oeth yl)bis[1,2]d ith iolo[3,4-b:4′,3′-e][1,4]-
th ia zin e-3,5-d ith ion e (9). Disulfur dichloride (2.65 mL, 33
mmol) was added dropwise to a solution of N-(2-diisopropyl-
aminoethyl)phthalimide14 (1f) (1 g, 3.65 mmol), DABCO (3.75
g, 33 mmol) in 1,2-dichloroethane (50 mL) at -40 °C. The
mixture was stirred for 15 min at -40 °C, then for 3 days at
room temperature and then refluxed for 1 h. The reaction
mixture was filtered through Celite and the solvent was
removed in the rotary evaporator. MPLC (petroleum ether to
CH2Cl2) of the residue afforded 9, black crystals (petroleum
1
3.92 (t, J 6.8, 2H, CH2); H NMR (400 MHz, pyridine-d5) δH
5.62 (t, J 6.0, 2H, CH2), 6.16 (t, J 6.0, 2H, CH2); 13C NMR (100
MHz, pyridine-d5) δC 38.67 and 43.01 (2 × CH2), 128.44,
129.41, 137.72, 139.62 and 148.34 (5 × sp2Ctertiary), 163.58 and
183.39 (2 × CdO); IR (CCl4, cm-1) νmax 1773, 1717, 1661 and
1
ether/CH2Cl2) (460 mg, 26%); mp 245-247 °C. H NMR (400
MHz, pyridine-d5) δH 4.15 (t, J 6.1, 2H, CH2), 5.18 (t, J 6.1,
2H, CH2), 7.55 (m, 2H, Ph), 7.79 (m, 2H, Ph); 13C NMR (100
MHz, pyridine-d5) δC 38.28 and 44.66 (2 × CH2, from DEPT),
123.27 and 134.29 (2 × CHaromatic, from DEPT), 132.64, 148.20
and 158.38 (3 × sp2Ctertiary), 168.42 (CdO), 203.23 (CdS); IR
(CCl4, cm-1) νmax 1768 and 1707 (CdO), 1392, 1306 (CdS); m/z
(EI, 70 eV) 484 (M+, 8), 452 (M - 32, 55), 420 (M - 64, 37),
174 (100); HRMS, M+ ) 483.8638 C16H8N2O2S7 requires
483.8631. Anal. Calcd for C16H8N2O2S7: C, 39.65; H, 1.66; N,
5.78. Found: C, 40.64; H, 1.84; N, 6.07.
1630 (CdO), 1521; m/z (EI, 70 eV) 592 (M+ + 4, 6), 590 (M+
+
2, 7), 588 (M+, 5), 560 (M + 4-32, 10), 558 (M + 2-32, 17),
556 (M - 32, 11), 273 (100). Anal. Calcd for C16H4Cl4N2O4S5:
C, 32.55; H, 0.68; N, 4.75. Found: C, 32.78; H, 0.71; N, 4.79.
Ack n ow led gm en t. We gratefully acknowledge fi-
nancial support from the Direccio´n General de Ensen˜an-
za Superior of Spain (DGES Project ref. PB96-0101), the
NATO Linkage Grant 970596, the Russian Foundation
for Basic Research (grant no. 99-03-32984a), MDL
Information Systems (UK) Ltd, and the Wolfson Foun-
dation for establishing the Wolfson Centre for Organic
Chemistry in Medical Science at Imperial College.
4-(2-P h th a lim id oeth yl)bis[1,2]d ith iolo[4,3-b:3′,4′-d ]p yr -
r ole-3,5-d ith ion e (10). Disulfur dichloride (2.65 mL, 33.1
mmol) was added dropwise to a solution of N-(2-diisopropyl-
aminoethyl)phthalimide14 (1f) and DABCO (3.75 g, 33 mmol)
in 1,2-dichlorobenzene (50 mL) at -40 °C. The mixture was
stirred for 15 min at -40 °C and then for 3 days at room
temperature and then refluxed for 1.5 h. The reaction mixture
was filtered through Celite, and the solvent was removed in
the rotary evaporator. MPLC (petroleum ether to CH2Cl2) of
the residue afforded 10, black crystals (petroleum ether/
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data (excluding structure factors) for the structures reported.
This material is available free of charge via the Internet at
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J O9902345