Synthesis of N-unsubstituted bis[1,2]dithiolo[1,4]thiazines and bis[1,2]dithiolopyrroles

Article abstract of DOI:10.1039/b005068g

The parent bis[1,2]dithiolo[1,4]thiazine-3,5-dione 8, -3,5-dithione 11, the unsymmetrical 3-oxo-5-thione 10 and the bis[1,2]dithiolopyrrole-3,5-dione 9 are synthesised by acid catalysed cleavage of their various N-benzyl, ethyl, ethoxycarbonylethyl and pr

Full text of DOI:10.1039/b005068g

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Synthesis of N-unsubstituted bis[1,2]dithiolo[1,4]thiazines and
bis[1,2]dithiolopyrroles
Lidia S. Konstantinova,a Natalia V. Obruchnikova,a Oleg A. Rakitin,a Charles W. Reesb and
Tomás Torrobac
1
a N. D. Zelinsky Institute of Organic Chemistry, Academy of Sciences, Leninsky Prospect, 47,
117913 Moscow, Russia
b Department of Chemistry, Imperial College of Science, Technology and Medicine, London,
UK SW7 2AY
c Departamento de Química, Facultad de Ciencias, Universidad de Burgos, 09001 Burgos, Spain
Received (in Cambridge, UK) 26th June 2000, Accepted 18th August 2000
First published as an Advance Article on the web 28th September 2000
The parent bis[1,2]dithiolo[1,4]thiazine-3,5-dione 8, -3,5-dithione 11, the unsymmetrical 3-oxo-5-thione 10 and
the bis[1,2]dithiolopyrrole-3,5-dione 9 are synthesised by acid catalysed cleavage of their various N-benzyl, ethyl,
ethoxycarbonylethyl and propanoic acid derivatives. These N-alkyl compounds are prepared in the usual way
from the appropriate N-alkyldiisopropylamine and S2Cl2. N-Benzyl derivatives 2 and 5 of the thiazine and pyrrole
diones give 8 (100%) and 9 (58%) respectively with conc. H2SO4 in dilute DCM solution, and the N-ethyl thiazine
derivatives of the dione 12 and the keto-thione 13 give 8 (89%) and 10 (75%) respectively in conc. H2SO4 at 120 ЊC.
Ethyl 3-(diisopropylamino)propanoate 16 with S2Cl2 gives the three thiazines 17 (30%), 18 (15%) and 19 (13%),
and 17 and 19 are converted into the pyrroles 20 (95%) and 21 (90%) respectively by thermal extrusion of sulfur in
refluxing xylene. All five ethyl esters, 17–21, are hydrolysed with aqueous acid to 22–26 respectively in 92–100% yield,
and the N-propanoic acids 22–25 with hot conc. hydrochloric or hot 80–90% sulfuric acid are dealkylated to the
corresponding parent products 8–11. It is also shown that the hydrolysis and dealkylation steps 17→22→8 can be
combined in one operation (75%).
We have previously described a remarkable one-pot transform-
ation of Hünig’s base and related diisopropylamines with
disulfur dichloride, S2Cl2, into bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e]-
[1,4]thiazines (cf. 2–4) and, at higher temperature, into
bis[1,2]dithiolo[4,3-b:3,4-d]pyrroles (cf. 5, 6), new families of
stable fully unsaturated heterocycles which are revealing a rich
chemistry.1–6 There has been greatly renewed interest in sulfur
heterocycles as new materials since the discovery of super-
conducting tetrathiafulvalene charge-transfer complexes7 and
molecular switches,8 thiazole and thiadiazole liquid crystals,9
and thiophene nonlinear optical materials.10 With such poten-
tial applications in mind, we wished to synthesise a wider range
of the bisdithiolothiazines and bisdithiolopyrroles, particularly
with various N-substituents, for which the N-unsubstituted
parent ring systems would hopefully be key intermediates. We
now describe various syntheses of these parent compounds
8–11.5
turned our attention to the synthesis of N-benzyl derivatives of
the ring systems, and their debenzylation.
N-Debenzylation reactions
Under minor variations of our standard conditions N-benzyl-
diisopropylamine 1,11 S2Cl2 and DABCO gave the three
N-benzyl bis[1,2]dithiolothiazines 2, 3 and 4 and two sym-
metrical bis[1,2]dithiolopyrroles 5 and 6, as shown in Scheme 1.
Our standard conditions for the above conversions are treat-
ment of the tertiary diisopropylamine with S2Cl2 and DABCO
for 3 d at room temperature, in chloroform for the thiazines,
and in chlorobenzene for the pyrroles; a final brief period of
heating for the latter induces extrusion of sulfur. For the oxy-
genated products, like 2, 3 and 5, formic acid is added to-
wards the end of the reaction. However, when these conditions
were applied to N,N-diisopropylamine and its trimethyl-
silyl derivative, there was extensive decomposition and no
N-unsubstituted dithiolothiazines or dithiolopyrroles could
be isolated. Diisopropylamines with readily removable, elec-
tron withdrawing groups like acetyl or cyano on nitrogen were
equally unsuccessful as starting materials, since they are inert
towards S2Cl2; the electron withdrawing groups presumably
suppress the initial oxidation of the amine by S2Cl2 to an
iminium ion.4 Since an N-benzyl group should be removable we
Scheme 1
When 1 was treated with S2Cl2 (10 equiv) and DABCO (7 equiv)
in CHCl3 for 3 d followed by formic acid (100 equiv), the
bisdithiolothiazinedione 2 was obtained in 35% yield. With
slightly more DABCO (9 equiv) the unsymmetrical keto-thione
DOI: 10.1039/b005068g
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3 was isolated in 14% yield. For the preparation of the dithione
4 (23%) we used a method developed for other bisdithiolo-
thiazine-dithiones,4 i.e. treatment of 1 with S2Cl2 and DABCO
and finally with triethylamine.
15 are readily available from Hünig’s base,4 we have investigated
their possible N-de-ethylation reactions. Whilst such reactions
are rare there is one report of the loss of an N-ethyl group
accompanying O-demethylation in a phenothiazine derivative
upon boiling in pyridine hydrochloride.12 However the diketo
derivative 12 was extensively decomposed under these
conditions, giving substantial amounts of sulfur but no clean
products of de-ethylation or sulfur extrusion. It was found
that compounds 12–15 are very sensitive to alkali but remark-
ably stable to acid. The thiazines 12–14 were stable to dilute
and conc. hydrochloric acid, even at reflux, and to dilute and
conc. sulfuric acid at room temperature. But on heating in conc.
sulfuric acid at 120 ЊC for 2 h, the diketo derivative 12 was
smoothly dealkylated to 8 in high yield (89%) (Scheme 4). The
The bisdithiolopyrroles 5 and 6 were prepared by the reaction
of 1 with S2Cl2 in chlorobenzene with a final period of heating
with and without formic acid, respectively. The yield of the
dione 5 was very low however (3%) and this compound was
prepared alternatively in excellent yield from the dithione 6
by treatment with an excess of ethoxycarbonylnitrile oxide 7
generated in situ from ethyl chlorooximinoacetate and triethyl-
amine,4 and from the bisdithiolothiazinedione 2 by sulfur extru-
sion in boiling xylene for 7 h (86% and 92% yield respectively).
The bisdithiolothiazinedithione 4 underwent similar but faster
thermolysis (in boiling xylene for 1 h) to give the corresponding
pyrrole 6 (88%).
The structures of these five N-benzyl derivatives, 2–6, fol-
lowed from their analytical and spectroscopic data and their
close similarity to the analogous N-ethyl compounds;4 the
structure of 2 was confirmed by X-ray crystallography.5 In gen-
eral the yields of N-benzyl derivatives from the S2Cl2 reactions
were lower than for the corresponding N-ethyl compounds,
probably because of their greater sensitivity to heat and to acid
(see below).
Very little is known about the N-debenzylation of 1,4-thi-
azines, 1,4-oxazines and piperazines, but cleavage of N-benzyl
tertiary amines is usually achieved by palladium catalysed
reductions. Compounds 2–6 are not stable to these reductive,
nor to strongly basic, conditions and so we examined their
behaviour under acidic conditions. Treatment of dilute solu-
tions of the two diketo compounds 2 and 5 in DCM with conc.
sulfuric acid gave the desired N-unsubstituted compounds 8
and 9 respectively (Scheme 2); 8 (100%) was formed rapidly, at
Scheme 4
monoketo derivative 13 behaved similarly to give the unsym-
metrical parent compound 10 (obtained in trace amounts only
from its N-benzyl derivative) in high yield (75%); this de-
ethylation of 13 was accompanied by a little oxidation to give
some of the diketo compound 8 as a minor product. When 13
was heated in trichloroacetic acid at 130 ЊC for 1 h it was
oxidised, without dealkylation, to give 12 (63%) together
with some extrusion of sulfur to the diketo pyrrole 15 (20%)
(Scheme 5).
Scheme 5
Scheme 2
The dithione 14 in conc. sulfuric acid at 135 ЊC for 3 h also
suffered some oxidation and de-ethylation to give the un-
symmetrical compound 10 (20%), together with traces of
the two symmetrical compounds 8 and 11 (Scheme 6). The
5–10 ЊC for 5 min, and 9 (58%) at room temperature overnight.
Their structures are based upon spectroscopic and analytical
data and confirmed for 8 by X-ray crystallography.5
However, when one or more of the keto groups in 2 and 5 are
replaced by thioketo groups, i.e. with compounds 3, 4 and 6, the
analogous debenzylations were unsuccessful. The bisdithiolo-
thiazines 3 and 4 were decomposed by conc. sulfuric acid in
DCM solution at room temperature within 10 min (Scheme 3);
Scheme 6
N-ethylbisdithiolopyrroles were unstable to hot conc. sulfuric
acid (125–130 ЊC) and compound 15 gave none of the N-H
compound 9.
N-Ethoxycarbonylethyl derivatives
Scheme 3
Given the above dealkylation reactions of the N-ethylbis-
dithiolothiazines in hot sulfuric acid, we wondered whether
compounds with functionalised ethyl groups would cleave
similarly, possibly under milder conditions. Such compounds,
with N-CH2CH2X groups, are generally readily available from
the appropriate diisopropylamine, Pri2NCH2CH2X, where X =
Cl, PhS, and phthalimido, for example.6 We were particularly
interested in the propanoic acids (X = CO2H) and their deriv-
atives, with the aim of investigating intramolecular attraction
between the ethyl group functionality and the sulfur atom in the
the NH compounds 10 and 11 (see below) were obtained only in
trace amounts and were identified by mass spectrometry. The
bisdithiolopyrrole 6 did not react under the same conditions;
the fused pyrroles are generally more stable than the thiazines.
Thus cleavage of the N-benzyl compounds was successful only
with the diketo compounds 2 and 5.
N-De-ethylation reactions
Since N-ethylbisdithiolothiazines 12–14 and bisdithiolopyrrole
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Table 1 Hydrolysis of esters 17–21 to the corresponding acids 22–26
acid
R–CH2CH2COOEt
17–21
R–CH2CH2COOH
22–26
Reaction conditions
Reaction
temperature/ЊC
Reaction
time/h
Product
(yield %)
Ester (mmol) R
Reagent
HCl (20%), 20 ml
60
60
60
60
15
22 (95)
23 (94)
24 (93)
25 (100)
H2SO4 (80%), 60 ml
H2SO4 (80%), 20 ml
HCl (20%), 60 ml
1
1
18
H2SO4 (80%), 40 ml
60
1
26 (92)
1,4-thiazine ring in the “scorpion” conformation adopted by
bisdithiolothiazines in the crystal lattice.4–6
We therefore studied the reaction of ethyl 3-(diisopropyl-
amino)propionate 1613 with S2Cl2 under our standard condi-
tions, and the results (Scheme 7) proved to be similar to those
the reaction mixture was then heated under reflux for 3 h, only
the dithione 19 was isolated, though in disappointing yield
(13%). The bisdithiolopyrroles 20 and 21 were obtained in high
yield (95 and 90% respectively) by sulfur extrusion from the
corresponding 1,4-thiazines upon heating in xylene. As with the
N-benzyl compounds above, the extrusion of sulfur from
dithione 19 was considerably faster than from the dione 17,
requiring 1 h and 18 h respectively for complete reaction.
The reaction of bisdithiolothiazines 17, 18 and 19 and bis-
dithiolopyrroles 20 and 21 with aqueous hydrochloric and
sulfuric acids was then studied. In each case the first step was a
very high yielding hydrolysis to the corresponding propanoic
acid (Table 1). The diketo compounds 17 and 20 were hydro-
lysed more readily (with more dilute hydrochloric acid) than
any of the thioketo analogues 18, 19 and 21. 1,4-Thiazino and
pyrrolo derivatives with the same number of thio and keto
groups had practically the same reactivity.
All the propanoic acids so produced are stable, high melting,
coloured compounds, practically insoluble in common organic
solvents and water. The diketo compounds 22 and 25 are
yellow, the monothione 23 is deep red and the dithiones 24 and
26 are deep purple. Their structures are based on spectroscopic
and analytical data and comparison with the corresponding
N-ethyl derivatives,4 and the structure of the diketo bisdithiolo-
thiazine acid 22 was confirmed by X-ray crystallography.14
Scheme 7
of the N-ethyl and N-benzyl compounds. The symmetrical
diketo compound 17 and the unsymmetrical monothione 18
were obtained from the amine 16, S2Cl2 and DABCO, with
subsequent treatment with formic acid. If the formic acid
was added after 3 d at room temperature compound 17 was
obtained in 30% yield, but if added after 7 d at room temper-
ature (in the presence of more DABCO) compound 18 was
isolated (15%). If formic acid was replaced by triethylamine and
N-Propanoic acid cleavage
We next studied the conversion of these propanoic acids into
the parent N-unsubstituted systems by more vigorous acidic
treatment; this was achieved in reasonable to high yields with
conc. hydrochloric acid (36%) at 100 ЊC, sulfuric acid (80
and 90%) at up to 135 ЊC and trichloroacetic acid at 130 ЊC
(Table 2).
J. Chem. Soc., Perkin Trans. 1, 2000, 3421–3427
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Table 2 N-Dealkylation of propanoic acids 22–25
Reaction conditions
Reaction
Propanoic acid
(mmol)
Reaction
time/h
Product
(yield %)
Reagent
temp./ЊC
HCl
(36%)
50 ml
100
10
26
2
H2SO4
(80%)
15 ml
107
135
H2SO4
(96%)
50 ml
24 (0.3)
Cl3CCO2H
14 g
130
100
2
8 (69)
HCl
35
(36%)
45 ml
The symmetrical diketo acid 22 with conc. hydrochloric acid
at 100 ЊC gave bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]thiazine-3,5-
dione 8 in high yield (80%). The monothione 23 required more
vigorous conditions, 80% sulfuric acid and a longer reaction
time, and the yield of 3-oxobis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]-
thiazine-5-thione 10 was substantially lower (40%). Under still
more vigorous conditions the dithione 24 gave a high yield of
the parent bisthione 11 (78%) though the reaction now had to
be performed under argon since 11 is unstable in air. Dithione
24 was also heated in trichloroacetic acid at 130 ЊC for 2 h,
when the only product isolated was the diketo compound 8
(69%), oxidation of both thio groups having accompanied
cleavage of the N-propanoic acid chain. Bisdithiolopyrrole
derivatives required more vigorous conditions for the same
cleavage. The pyrrolo-propanoic acid 25 in conc. hydrochloric
acid at 100 ЊC had to be heated for longer than the thiazino-
propanoic acid 22 and the yield of the pyrrole 9 (56%) was
lower than that of the thiazine 8 (80%). In conc. sulfuric acid at
130 ЊC both pyrrole derivatives 25 and 26 decomposed within a
few hours.
loss of the alkyl group by nucleophilic attack or by elimination.
The benzyl group is cleaved most readily, as expected, followed
by the propanoic acid group, and then the ethyl group. A rare
acid-catalysed N-de-ethylation of a phenothiazine with boiling
pyridine hydrochloride was mentioned earlier.12
A somewhat related, but thermal cleavage of an N-propanoic
acid residue has been reported.15 When 27 was heated neat at
250 ЊC under reduced pressure (0.1 mm) it gave 29 in almost
quantitative yield. Curiously this transformation was struc-
ture specific, being observed only when both fused benzene
rings were present. The reaction could possibly be self (acid)
catalysed via the zwitterionic form 28 with the proton trans-
We have shown that the ethyl propanoate 17 is hydrolysed to
the propanoic acid 22 (95%) in dilute hydrochloric acid at 60 ЊC
for 15 h and that the acid 22 is cleaved to the parent compound
8 (80%) in conc. hydrochloric acid at 100 ЊC for 1 h. As one
might expect these two steps can be combined and the ester 17
was converted directly into 8 in virtually the same overall yield
(75%) by heating in conc. sulfuric acid at 95 ЊC for 20 h. The
analogous sequence 18→23→10 could probably be combined
in the same way. The parent compound 8 can also be prepared
quite readily via its N-ethyl and N-benzyl derivatives, 12 and 2,
whilst the monothio analogue 10 is best prepared via its N-ethyl
derivative 13.
Of the three N-unsubstituted bisdithiolothiazines, 8 and 10
are thermally stable, and may be kept in air though both darken
on storage in the light. Bisthione 11 however is unstable in air at
room temperature or adsorbed onto silica gel, giving 10; all
operations involving 11 should be performed under argon.
All the above acid-catalysed dealkylation reactions presum-
ably involve protonation of the substrates on one, or more, of
the several available hetero atoms (N, S or O) followed by
ferred to the carbonyl group, giving a tautomer which would
be greatly stabilised by the second benzo ring. However this
thermal cleavage did not extend to our N-propanoic acid
22, nor its ethyl ester 17, since on heating at 200–220 ЊC/0.5
mm both of these compounds underwent preferential sulfur
extrusion and sublimation to give the corresponding pyrroles 25
and 20 quantitatively.
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as dark red crystals (from light petroleum–CHCl3), mp 221–
Experimental
Melting points were determined on a Kofler hot-stage appar-
222 ЊC (Found Mϩ, 400.8606. C13H7NS7 requires M, 400.8624)
(Found: C, 38.7; H, 1.6; N, 3.2. C13H7NS7 requires C, 38.9; H,
1.8; N, 3.5%); δH (d5-pyridine) 5.45 (2H, s, CH2), 7.31 and 7.38
atus and are uncorrected. IR spectra were recorded on a Perkin-
Elmer 298 instrument in KBr pellets. H NMR and 13C NMR
1
(5H, m, Ph); δ (d -pyridine) 203.87 (C᎐S), 159.74, 147.86 and
᎐
C
5
spectra were recorded on a Bruker DRX 400. CH groups were
identified by DEPT experiments. J-values are given in Hz.
Mass spectra were recorded on VG7070E and VG-AutoSpec
instruments using electron impact ionisation. Light petroleum
refers to the fraction bp 40–60 ЊC.
137.76 (3 × sp2 tertiary C), 129.82, 128.82, and 128.42 (3 C-H),
51.76 (CH2); νmax/cmϪ1 1630, 1480, 1450, 1330, 1300, 1110,
1050, 940, 850, 700; m/z 401 (Mϩ, 70%), 369 (45), 310 (52), 279
(50), 246 (53), 210 (85), 158 (36), 100 (40), 91 (100), 65 (50).
4-Benzyl-3H-bis[1,2]dithiolo[4,3-b:3,4-d]pyrrole-3,5(4H)-dione
5
4-Benzyl-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј,-e][1,4]-
thiazine-3,5-dione 2
Method A. Disulfur dichloride (4.0 ml, 50 mmol) was added
dropwise at Ϫ15 to Ϫ20 ЊC to a stirred solution of N-benzyl-
diisopropylamine 1 (0.95 g, 5 mmol) and DABCO (3.92 g, 35
mmol) dissolved in chlorobenzene (100 ml). The mixture was
stirred for 15 min at Ϫ20 ЊC and at room temperature for 72 h.
Formic acid (3.76 ml, 100 mmol) was added dropwise at 5 ЊC,
the mixture was stirred for 1 h at room temperature, refluxed for
48 h, filtered and the solvent was removed under reduced pres-
sure. The residue was separated by column chromatography
(silica, light petroleum, and then light petroleum–DCM mix-
tures) to give the title compound 5 (50 mg, 3%) as yellow crystals
(from light petroleum–CHCl3), mp 211–213 ЊC (Found Mϩ,
336.9345. C13H7NO2S4 requires M, 336.9360) (Found: C, 46.2;
H, 2.2; N, 4.0. C13H7NO2S4 requires C, 46.3; H, 2.1; N, 4.1%);
δH (CDCl3) 5.70 (2H, s, CH2), 7.31 and 7.41 (5H, m, Ph);
δC (CDCl ) 181.49 (C᎐O), 136.53, 135.26 and 130.88 (3 × sp2
Disulfur dichloride (4.0 ml, 50 mmol) was added dropwise at
Ϫ15 to Ϫ20 ЊC to a stirred solution of N-benzyldiisopropyl-
amine 1 (5 mmol) and DABCO (3.92 g, 35 mmol) dissolved in
chloroform (100 ml). Then the mixture was stirred for 15 min at
Ϫ20 ЊC and at room temperature for 72 h. Formic acid (3.76 ml,
100 mmol) was added dropwise at 5 ЊC, the mixture was stirred
for 1 h at room temperature, refluxed for 1 h, filtered and
solvent was removed under reduced pressure. The residue was
separated by column chromatography (silica, light petroleum,
and then light petroleum–DCM mixtures) to give the title com-
pound 2 (650 mg, 35%) as yellow crystals (from light petroleum–
CHCl3), mp 200–202 ЊC (Found Mϩ, 368.9080. C13H7NO2S5
requires M, 368.9080) (Found: C, 42.5; H, 1.8; N, 3.5. C13H7-
NO2S5 requires C, 42.2; H, 1.9; N, 3.8%); δH (CDCl3) 4.85 (2H,
s, CH2), 7.34 (5H, m, Ph); δC (CDCl ) 182.31 (C᎐O), 147.00,
᎐
3
137.33 and 136.49 (3 × sp2 tertiary C), 128.83, 128.62 and
᎐
3
tertiary C), 128.86, 128.50 and 128.38 (3 C-H), 47.02 (CH2);
128.35 (3 C–H), 50.77 (CH2); νmax/cmϪ1 3020 and 2960 (CH),
νmax/cmϪ1 1640 (C᎐O), 1490, 1420, 1360, 1230, 1100, 1070, 850,
᎐
1630 (C᎐O), 1550, 1510, 1450, 1340, 1260, 1130, 1050, 940, 710;
᎐
820, 770; m/z 337 (Mϩ, 41%), 304 (4), 215 (9), 182 (2), 149 (3),
m/z 369 (Mϩ, 27%), 278 (20), 218 (6), 126 (10), 114 (23), 102
123 (10), 91 (100), 65 (15).
(11), 91 (100), 65 (82).
Method B. Triethylamine (0.42 ml, 3.0 mmol) was added
dropwise to a solution of dithione 6 (0.22 g, 0.6 mmol) and
ethyl chlorooximidoacetate (0.36 g, 2.4 mmol) in dry THF (10
ml) at 0 ЊC. The mixture was stirred for 15 min at 0 ЊC and a
further 15 min at room temperature. The reaction mixture was
filtered through Celite, and the solvent was removed in the
rotary evaporator. The residue was subjected to MPLC (petrol-
eum ether to DCM) to give the title compound 5 (170 mg, 86%)
identical with the above specimen.
4-Benzyl-3-oxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]-
thiazine-5-thione 3
Disulfur dichloride (4.0 ml, 50 mmol) was added dropwise at
Ϫ15 to Ϫ20 ЊC to a stirred solution of N-benzyldiisopropyl-
amine 1 (5 mmol) and DABCO (5.04 g, 45 mmol) dissolved in
chloroform (100 ml). Then the mixture was stirred for 15 min
at Ϫ20 ЊC and at room temperature for 144 h. Formic acid
(3.76 ml, 100 mmol) was added dropwise at 5 ЊC, the reaction
mixture was refluxed for 1 h, filtered and solvent was removed
under reduced pressure. The residue was separated by column
chromatography (silica, light petroleum, and then light
petroleum–DCM mixtures) to give the title compound 3 (260
mg, 14%) as orange crystals (from light petroleum–CHCl3), mp
209–210 ЊC (Found Mϩ, 384.8864. C13H7NOS6 requires M,
384.8852) (Found: C, 40.4; H, 1.8; N, 3.5. C13H7NOS6 requires
C, 40.5; H, 1.8; N, 3.6%); δH (CDCl3) 4.97 (2H, br s, CH2), 7.28
4-Benzyl-3H-bis[1,2]dithiolo[4,3-b:3,4-d]pyrrole-3,5(4H)-
dithione 6
Disulfur dichloride (4.0 ml, 50 mmol) was added dropwise at
Ϫ15 to Ϫ20 ЊC to a stirred solution of N-benzyldiisopropyl-
amine 1 (0.95 g, 5 mmol) and DABCO (6.1 g, 50 mmol) dis-
solved in chlorobenzene (100 ml). Then the mixture was stirred
for 15 min at Ϫ20 ЊC and at room temperature for 72 h. The
mixture was boiled for 2 h, filtered and the solvent was removed
under reduced pressure. The residue was separated by column
chromatography (silica, light petroleum, and then light
petroleum–DCM mixtures) to give the title compound 6 (240
mg, 13%) as black crystals (from light petroleum–CHCl3),
mp 223–224 ЊC (Found Mϩ 368.8926. C13H7NS6 requires M,
368.8903) (Found: C, 42.1; H, 1.9; N, 3.8. C13H7NS6 requires C,
42.45; H, 1.9; N, 3.8%); δH (d5-pyridine) 5.88 (2H, s, CH2), 7.52
and 7.35 (5H, m, Ph); δ (CDCl ) 203.21 (C᎐S), 183.90 (C᎐O),
᎐
᎐
C
3
159.11, 150.98, 147.46, 138.01 and 136.51 (5 × sp2 tertiary C),
129.36, 129.02 and 128.32 (3 C-H), 51.76 (CH2); νmax/cmϪ1 1620
(C᎐O), 1540, 1440, 1320, 1280, 1090, 1020, 700; m/z 385 (Mϩ,
᎐
27%), 369 (7), 353 (10), 294 (29), 276 (13), 263 (16), 234 (14),
192 (8), 149 (11), 126 (7), 114 (12), 91 (100), 65 (21).
4-Benzyl-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]thiazine-
3,5-dithione 4
and 7.60 (5H, m, Ph); δC (d -pyridine) 200.44 (C᎐S), 143.52,
᎐
5
Disulfur dichloride (4.0 ml, 50 mmol) was added dropwise at
Ϫ15 to Ϫ20 ЊC to a stirred solution of N-benzyldiisopropyl-
amine 1 (5 mmol) and DABCO (6.1 g, 50 mmol) dissolved in
chloroform (100 ml). Then the mixture was stirred for 15 min at
Ϫ20 ЊC and at room temperature for 72 h. Triethylamine (6.57
g, 50 mmol) was added dropwise, the mixture was stirred for 3 h
at room temperature, filtered and solvent was removed under
reduced pressure. The residue was separated by column chrom-
atography (silica, light petroleum, and then light petroleum–
DCM mixtures) to give the title compound 4 (460 mg, 23%)
139.94 and 137.20 (3 × sp2 tertiary C), 128.77, 127.47 and
127.22 (3 C-H), 42.69 (CH2); νmax/cmϪ1 1470, 1450, 1350, 1100,
840, 730; m/z 369 (Mϩ, 75%), 336 (15), 305 (12), 272 (10), 247
(45), 138 (12), 121 (22), 112 (22), 100 (25), 91 (100), 65 (35).
Sulfur extrusion from 2 and 4
A solution of 2 or 4 (1 mmol) in xylene (100 ml) was boiled
for 7 or 1 h respectively. The solvent was removed in a rotary
evaporator, the residue was washed with light petroleum and
J. Chem. Soc., Perkin Trans. 1, 2000, 3421–3427
3425

View Article Online
Table 3 Acid hydrolysis and cleavage of bisdithiolo-thiazines and
-pyrroles
crystallised from light petroleum–chloroform mixtures to give
5 (92%) or 6 (88%) identical with the above specimens.
Reaction conditions
Reagent
Treatment of 4-ethyl-3-oxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:
4Ј,3Ј-e][1,4]thiazine-5-thione 13 with trichloroacetic acid
Starting
material
(mmol)
Reaction Reaction Product
temp./ЊC
time/h
(yield %)
A mixture of compound 13 (32 mg, 0.1 mmol) and trichloro-
acetic acid (15 g) was heated at 130 ЊC for 1 h. After cooling the
reaction mixture was diluted with water (100 ml), extracted
with DCM and the organic solution was dried over MgSO4.
After evaporation the residue was subjected to column chrom-
atography (silica, light petroleum, and then light petroleum–
DCM mixtures) to give 4-ethyl-3H-bis[1,2]dithiolo[4,3-b:3,4-d]-
pyrrole-3,5-dione 15 (5 mg, 20%) with mp 199–200 ЊC and 4-
ethylbis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]thiazine-3,5(4H)-dione
12 (18 mg, 63%) with mp 191–193 ЊC.4
2 (0.3)
6 (0.3)
H2SO4 (96%), 0.6 mla
H2SO4 (96%), 0.6 mla
12 (0.15) H2SO4 (96%), 20 ml
H2SO4 (96%), 20 ml
H2SO4 (96%), 20 ml
a In dichloromethane (40 ml).
5–10
20
120
125
135
0.08
20
2
2
3
8 (100)
9 (58)
8 (89)
13 (0.1)
14 (0.1)
10 (75)
10 (40)
crystallised from light petroleum–chloroform mixtures to give
the following compounds.
Preparation of compounds 17–19
Ethyl 3-(3,5-dioxo-3H,5H-[4,3-b:3,4-d]bis[1,2]dithiolopyrrol-
4-yl)propanoate 20. Yellow crystals (95%), mp 147–148 ЊC (from
light petroleum–CHCl3) (Found Mϩ, 346.9404. C11H9NO4S4
requires M, 346.9414) (Found: C, 37.8; H, 2.5; N, 3.9.
C11H9NO4S4 requires C, 38.0; H, 2.6; N, 4.0%); δH (CDCl3)
1.21 (3H, t, J 7.1, CH3), 2.84 (2H, t, J 7.0, CH2), 4.09 (2H, t,
Ethyl 3-(diisopropylamine)propionate 1613 was treated with
S2Cl2 exactly as for the conversions of N-benzyldiisopropyl-
amine 1 into 2, 3 and 4 to give compounds 17, 18 and 19,
respectively.
Ethyl 3-(3,5-dioxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e]-
[1,4]thiazin-4-yl)propanoate 17. Yellow crystals (30%), mp
135–136 ЊC (from light petroleum–CHCl3) (Found Mϩ,
378.9125. C11H9NO4S5 requires M, 378.9135) (Found: C, 34.9;
H, 2.4; N, 3.6. C11H9NO4S5 requires C, 34.8; H, 2.4; N, 3.7%);
δH (CDCl3) 1.21 (3H, t, J 7.1, CH3), 2.64 (2H, t, J 6.4, CH2),
J 7.1, CH ), 4.82 (2H, t, J 7.0, CH ); δ (CDCl ) 181.24 (C᎐O),
᎐
2
2
C
3
170.02 (C᎐O), 135.53 and 130.51 (2 × sp2 tertiary C), 60.97
᎐
(CH2), 39.74 (CH2), 35.65 (CH2), 14.03 (CH3); νmax/cmϪ1 2980
(CH), 1710 (C᎐O), 1660, 1620, 1440, 1330, 1290, 1190, 1100,
᎐
930, 850; m/z 347 (Mϩ, 65%), 302 (14), 287 (16), 273 (12),
259 (28), 247 (18), 231 (12), 182 (10), 126 (10), 96 (20), 55
(100).
4.10 (4H, m, 2 CH ); δ (CDCl ) 181.99 (C᎐O), 171.30 (C᎐O),
᎐
᎐
2
C
3
146.74 and 136.52 (2 × sp2 tertiary C), 60.94 (CH2), 42.34
(CH2), 34.66 (CH2), 14.16 (CH3); νmax/cmϪ1 2980 (CH), 1730
Ethyl
3-(3,5-dithioxo-3H,5H-bis[1,2]dithiolo[4,3-b:3,4-d]-
(C᎐O), 1660, 1630, 1550, 1510, 1440, 1380, 1260, 1210, 1180,
᎐
pyrrol-4-yl)propanoate 21. Black crystals (90%), mp 172–174 ЊC
(from light petroleum–CHCl3) (Found Mϩ, 378.8945.
C11H9NO2S6 requires M, 378.8958) (Found: C, 34.6; H, 2.3; N,
3.45. C11H9NO2S6 requires C, 34.8; H, 2.4; N, 3.7%); δH (d5-
pyridine) 1.15 (3H, t, J 7.1, CH3), 3.20 (2H, t, J 8.0, CH2), 4.15
(2H, q, J 7.1, CH2), 5.92 (2H, t, J 8.0, CH2); δC (d5-pyridine)
200.05 (C᎐S), 170.74 (C᎐O), 145.69 and 137.15 (2 × sp2 tertiary
1080, 1010, 830; m/z 379 (Mϩ, 100%), 292 (71), 279 (52), 262 (8),
251 (9), 219 (14), 175 (9), 114 (17), 101 (39), 88 (19), 73 (34), 55
(34).
Ethyl
3-(3-oxo-5-thioxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:
4Ј,3Ј-e][1,4]thiazin-4-yl)propanoate 18. Orange crystals (15%),
mp 154–155 ЊC (from light petroleum–CHCl3) (Found Mϩ,
394.8915. C11H9NO3S6 requires M, 394.8907) (Found: C, 33.6;
H, 2.3; N, 3.4. C11H9NO3S6 requires C, 33.4; H, 2.3; N, 3.5%);
δH (d5-pyridine) 1.08 (3H, t, J 7.1, CH3), 2.82 (2H, t, J 6.5,
CH2), 4.05 (2H, q, J 7.1, CH2), 4.62 (2H, br s, CH2); δC (d5-
᎐
᎐
C), 61.05 (CH2), 37.06 (CH2), 36.34 (CH2), 14.36 (CH3); νmax
/
cmϪ1 2920 (C-H), 1710 (C᎐O), 1430, 1410, 1350, 1280, 1180,
᎐
1040, 850; m/z 379 (Mϩ, 100%), 347 (12), 306 (32), 279 (22), 248
(18), 192 (15), 160 (23), 112 (21), 64 (32).
pyridine) 203.37 (C᎐S), 183.78 (C᎐O), 171.85 (C᎐O), 158.70,
᎐
᎐
᎐
General procedure for the hydrolysis and cleavage of bisdithiolo-
thiazines and pyrroles
150.74, 147.84 and 136.98 (4 × sp2 tertiary C), 61.01 (CH2),
43.84 (CH2), 34.60 (CH2), 14.32 (CH3); νmax/cmϪ1 2980 (CH),
The bisdithiolo-thiazine or -pyrrole was mixed with acid and
stirred at the temperature and for the time given in Tables 1, 2
and 3. Then the reaction mixture was diluted with water,
extracted with DCM and the organic solution was dried over
MgSO4. After evaporation the residue was subjected to column
chromatography (silica, light petroleum, and then light
petroleum–DCM mixtures). Reaction details and product
yields are given in Tables 1, 2 and 3.
1720 (C᎐O), 1620, 1540, 1470, 1440, 1340, 1290, 1180, 1060,
᎐
1010; m/z 395 (Mϩ, 100%), 307 (82), 295 (34), 263 (55), 235 (16),
126 (22), 114 (24), 100 (47), 88 (33), 70 (29), 55 (32).
Ethyl 3-(3,5-dithioxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-
e][1,4]thiazin-4-yl)propanoate 19. Dark red crystals (13%),
mp 181–182 ЊC (from light petroleum–CHCl3) (Found Mϩ,
410.8686. C11H9NO2S7 requires M, 410.8678) (Found: C, 31.9;
H, 2.2; N, 3.4. C11H9NO2S7 requires C, 32.1; H, 2.2; N, 3.4%);
δH (d5-pyridine) 1.07 (3H, t, J 7.2, CH3), 2.87 (2H, t, J 6.8,
CH2), 4.05 (2H, q, J 7.1, CH2), 4.85 (2H, t, J 6.8, CH2); δC (d5-
Characterisation of products not already given are as follows.
3H,4H,5H-Bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]thiazine-3,5-
dione 8. Yellow crystals, mp 222–224 ЊC (Found Mϩ, 278.8600.
C6HNO2S5 requires M, 278.8611) (Found: C, 25.8; H, 0.3; N,
4.8. C6HNO2S5 requires C, 25.8; H, 0.4; N, 5.0%); δH (CDCl3)
pyridine) 203.60 (C᎐S), 171.61 (C᎐O), 159.01 and 148.11
᎐
᎐
(2 × sp2 tertiary C), 60.75 (CH2), 43.70 (CH2), 34.37 (CH2),
14.07 (CH3); νmax/cmϪ1 1730 (C᎐O), 1500, 1460, 1310, 1090,
᎐
5.99 (1H, br s, NH); δC (CDCl ) 180.91 (C᎐O), 133.81 and
1070, 1000, 980, 930; m/z 411 (Mϩ, 68%), 395 (21), 378 (23), 323
(31), 307 (20), 279 (29), 246 (32), 126 (31), 100 (96), 84 (100), 70
(60), 64 (48), 49 (100).
᎐
3
128.78 (2 × sp2 tertiary C); νmax/cmϪ1 3320 (NH), 1640 C᎐O),
᎐
1590, 1550, 1470, 1280, 1060, 850, 800; m/z 279 (Mϩ, 100%),
251 (13), 219 (8), 175 (14), 159 (11), 115 (8), 88 (21).
Sulfur extrusion from 17 and 19
3H-Bis[1,2]dithiolo[4,3-b:3,4-d]pyrrole-3,5(4H)-dione
9.
A solution of 17 or 19 (1 mmol) in xylene (100 ml) was boiled
for 18 or 1 h respectively. The solvent was removed in a rotary
evaporator, the residue was washed with light petroleum and
Yellow crystals, mp 267–268 ЊC (Found Mϩ, 246.8873.
C6HNO2S4 requires M, 246.8890) (Found: C, 29.0; H, 0.3; N,
5.3. C6HNO2S4 requires C, 29.1; H, 0.4; N, 5.7%); δH (CDCl3)
3426
J. Chem. Soc., Perkin Trans. 1, 2000, 3421–3427

View Article Online
3.77 (1H, br s, NH); δC (D SO ) 182.80 (C᎐O), 140.27 and
1230, 1210, 1180, 1100, 860; m/z 319 (Mϩ, 88%), 247 (38), 231
(32), 182 (14), 126 (13), 100 (30), 94 (32), 88 (26), 70 (28), 64
(60), 55 (100).
᎐
2
4
138.96 (2 × sp2 tertiary C); νmax/cmϪ1 3150 (NH), 1665 C᎐O),
᎐
1640, 1460, 1230, 1100, 840; m/z 247 (Mϩ, 100%), 251 (13), 219
(8), 191 (9), 126 (4), 100 (12), 96 (16), 83 (21).
3-(3,5-Dithioxo-3H,5H-bis[1,2]dithiolo[4,3-b:3,4-d]pyrrol-4-
yl)propanoic acid 26. Black crystals, mp 273–274 ЊC (Found
Mϩ, 378.8958. C9H5NO2S7 requires M, 378.8930) (Found: C,
30.5; H, 1.4; N, 3.8. C9H5NO2S6 requires C, 30.75; H, 1.4; N,
4.0%); δH (d5-pyridine) 3.34 (2H, t, J 8.2, CH2), 5.96 (2H, t,
3-Oxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]thiazine-
5-thione 10. Dark red crystals, mp 253–255 ЊC (Found Mϩ,
294.8379. C6HNOS6 requires M, 294.8382) (Found: C, 24.6;
H, 0.3; N, 4.9. C6HNOS6 requires C, 24.4; H, 0.3; N, 4.7%);
δH (d5-pyridine) 6.61 (1H, br s, NH); δC (d5-pyridine) 194.92
(C᎐S), 182.00 (C᎐O), 150.65, 144.55, 138.52 and 133.65 (4 × sp2
J 8.2, CH2); δC (d -pyridine) 199.58 (C᎐O), 172.74 (C᎐O),
᎐
᎐
5
145.20 and 136.65 (2 × sp2 tertiary C) 40.12 (CH2), 36.14 (CH2);
᎐
᎐
tertiary C); νmax/cmϪ1 1640 (C᎐O), 1580, 1450, 1320, 1110, 1030,
νmax/cmϪ1 2920 (CH), 1710 (C᎐O), 1630, 1430, 1350, 1280, 1130,
᎐
᎐
860, 740; m/z 295 (Mϩ, 100%), 235 (15), 191 (27), 159 (22), 126
1110, 1040, 930, 850; m/z 351 (Mϩ, 46%), 335 (12), 306 (22), 279
(22), 247 (30), 215 (21), 138 (30), 126 (42), 112 (100), 100 (88),
88 (45), 55 (78).
(18), 100 (37), 88 (29).
3H,4H,5H-Bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]thiazine-3,5-
dithione 11. Black crystals, mp 270–272 ЊC (Found Mϩ,
310.8158. C6HNS7 requires M, 310.8154); δH (d5-pyridine) 3.48
Acknowledgements
(1H, br s, NH); δC (d -pyridine) 199.62 (C᎐S), 158.32 and
᎐
5
We gratefully acknowledge financial support from the Dirección
General de Enseñanza Superior of Spain (DGES Project ref.
PB96-0101), the Royal Society, the Russian Foundation for
Basic Research (grant no. 99-03-32984a), an RSC Research
Fund Grant to O. A. R. and MDL Information Systems (UK)
Ltd, and we thank the Wolfson Foundation for establishing the
Wolfson Centre for Organic Chemistry in Medical Science at
Imperial College.
148.52 (2 × sp2 tertiary C); νmax/cmϪ1 3310 (NH), 1590, 1500,
1320, 1120, 1020, 890; m/z 311 (Mϩ, 8%), 279 (13), 175 (6), 124
(18), 115 (6), 88 (18), 76 (34), 62 (54), 44 (100).
3-(3,5-Dioxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e][1,4]-
thiazin-4-yl)propanoic acid 22. Yellow crystals, mp 209–210 ЊC
(Found Mϩ, 350.8824. C9H5NO4S5 requires M, 350.8822)
(Found: C, 30.8; H, 1.6; N, 3.9. C9H5NO4S5 requires C, 30.8; H,
1.4; N, 4.0%); δH (d5-pyridine) 2.97 (2H, t, J 6.5, CH2), 4.53 (2H,
t, J 6.5, CH2); δC (d -pyridine) 183.67 (C᎐O), 174.38 (C᎐O),
᎐
᎐
5
References
149.11 and 136.68 (2 × sp2 tertiary C) 44.20 (CH2), 35.07 (CH2);
1 C. F. Marcos, C. Polo, O. A. Rakitin, C. W. Rees and T. Torroba,
Angew. Chem., Int. Ed. Engl., 1997, 36, 281.
2 C. F. Marcos, C. Polo, O. A. Rakitin, C. W. Rees and T. Torroba,
Chem. Commun., 1997, 879.
νmax/cmϪ1 2960 (CH), 1710 (C᎐O), 1620, 1550, 1510, 1450, 1260,
᎐
1020, 980, 830, 800; m/z 351 (Mϩ, 12%), 327 (6), 292 (8), 279 (8),
236 (14), 213 (7), 105 (100), 91 (58), 77 (78), 70 (48).
3 C. F. Marcos, O. A. Rakitin, C. W. Rees, L. I. Souvorova,
T. Torroba, A. J. P. White and D. J. Williams, Chem. Commun., 1998,
453.
4 C. W. Rees, A. J. P. White, D. J. Williams, O. A. Rakitin,
C. F. Marcos, C. Polo and T. Torroba, J. Org. Chem., 1998, 63, 2189.
5 For a preliminary communication of some of this work, see
C. F. Marcos, O. A. Rakitin, C. W. Rees, T. Torroba, A. J. P. White
and D. J. Williams, Chem. Commun., 1999, 29.
3-(3-Oxo-5-thioxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e]-
[1,4]thiazin-4-yl)propanoic acid 23. Dark red crystals, mp
218–219 ЊC (Found Mϩ, 366.8563. C9H5NO3S6 requires M,
366.8594) (Found: C, 29.4; H, 1.5; N, 3.6. C9H5NO3S6 requires
C, 29.4; H, 1.4; N, 3.8%); δH (d5-pyridine) 3.02 (2H, t, J 6.6,
CH2), 4.78 (2H, br s, CH2); δC (d -pyridine) 203.10 (C᎐S),
᎐
5
6 C. W. Rees, A. J. P. White, D. J. Williams, O. A. Rakitin, L. S.
Konstantinova, C. F. Marcos and T. Torroba, J. Org. Chem., 1999,
64, 5010; S. Barriga, L. S. Konstantinova, C. F. Marcos, O. A.
Rakitin, C. W. Rees, T. Torroba, A. J. P. White and D. J. Williams,
J. Chem. Soc., Perkin Trans. 1, 1999, 2237.
7 J. C. Williams, A. J. Schultz, U. Geiser, K. D. Carlson, A. M. Kini,
H. H. Wang, W. K. Kwok, M. H. Whangbo and J. E. Schirber,
Science, 1991, 252, 1501; M. R. Bryce, Chem. Soc. Rev., 1991, 20,
355; J. Garin, Adv. Heterocycl. Chem., 1995, 62, 249; Y. Misaki,
N. Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and S.
Tanaka, Angew. Chem., Int. Ed. Engl., 1995, 34, 1222.
8 T.Jorgensen,T.K.HansenandJ.Becher,Chem.Soc.Rev.,1994,23,41;
W. F. Jager, J. C. de Jong, B. de Lange, N. P. M. Huck, A. Meetsma
and B. L. Feringa, Angew. Chem., Int. Ed. Engl., 1995, 34, 348;
G. M. Tsivgoulis and J.-M. Lehn, Angew. Chem., Int. Ed. Engl.,
1995, 34, 1119; M. B. Nielsen, C. Lomholt and J. Becher, Chem. Soc.
Rev., 2000, 29, 153.
183.90 (C᎐O), 174.40 (C᎐O), 158.74, 150.95, 148.09 and 137.19
᎐
᎐
(4 × sp2 tertiary C), 44.60 (CH2), 35.04 (CH2); νmax/cmϪ1 2930
(CH), 1700 (C᎐O), 1630, 1470, 1340, 1290, 1260, 1100, 1020,
᎐
830; m/z 367 (Mϩ, 55%), 351 (52), 335 (100), 319 (25), 307 (30),
263 (42), 126 (27), 100 (100), 76 (100), 64 (100).
3-(3,5-Dithioxo-3H,4H,5H-bis[1,2]dithiolo[3,4-b:4Ј,3Ј-e]-
[1,4]thiazin-4-yl)propanoic acid 24. Black crystals, mp 216–
217 ЊC (Found Mϩ, 382.8374. C9H5NO2S7 requires M,
382.8365) (Found: C, 28.6; H, 1.2; N, 3.5. C9H5NO2S7 requires
C, 28.2; H, 1.3; N, 3.7%); δH (d5-pyridine) 3.03 (2H, t, J 7.0,
CH2), 4.95 (2H, t, J 7.0, CH2); δC (d -pyridine) 203.69 (C᎐S),
᎐
5
174.35 (C᎐O), 158.96 and 148.31 (2 × sp2 tertiary C), 44.51
᎐
(CH2), 34.86 (CH2); νmax/cmϪ1 2930 (CH), 1700 (C᎐O), 1500,
᎐
1450, 1310, 1060, 930, 740; m/z 383 (Mϩ, 25%), 351 (100), 311
9 P. Day, D. C. Bradley and D. Bloor, Molecular Chemistry for
Electronics, The Royal Society, London, 1990, p. 1.
(10), 295 (8), 279 (12), 247 (15), 204 (8), 138 (8), 112 (6), 88 (10).
10 A. K. Y. Jen, V. P. Rao, K. Y. Wong and K. J. Drost, Chem. Commun.,
1993, 90.
11 N. C. Deno and R. E. Fruit, J. Am. Chem. Soc., 1968, 90, 3502.
12 B. Lobert, G. Saint-Ruf and N. P. Buu-Hoï, Bull Soc. Chim. Fr.,
1971, 3251.
3-(3,5-Dioxo-3H,5H-bis[1,2]dithiolo[4,3-b:3,4H-d]pyrrol-4-
yl)propanoic acid 25. Yellow crystals, mp 239–240 ЊC (Found:
C, 33.8; H, 1.4; N, 4.2. C9H5NO4S4 requires C, 33.9; H, 1.6; N,
4.4%); δH (d5-pyridine) 3.18 (2H, t, J 7.5, CH2), 5.10 (2H, t,
13 S. I. Suminov, Moscow Univ. Chem Bull. (Engl. Transl.), 1967, 22, 75
J 6.5, CH2); δC (d -pyridine) 182.28 (C᎐O), 172.90 (C᎐O),
᎐
᎐
5
(Chem Abstr., 1967, 67, 21425r).
149.05 and 131.40 (2 × sp2 tertiary C) 40.29 (CH2), 36.31 (CH2);
14 A. J. P. White and D. J. Williams, unpublished work.
15 J. T. Braunholtz and F. G. Mann, J. Chem. Soc., 1954, 651.
νmax/cmϪ1 3250 (OH), 1720 (C᎐O), 1630, 1600, 1430, 1340, 1300,
᎐
J. Chem. Soc., Perkin Trans. 1, 2000, 3421–3427
3427