Synthesis and reactions of new dithiolopyrroles

Article abstract of DOI:10.1002/hlca.200290022

The title compounds were prepared starting from pyrrolinone 4. Nucleophilic-displacement and ring-closure reactions yielded the dithiolopyrrole 5a, which formed salts with electrophiles (7, 8) as well as with bases. The crystal structure of 5a was determined. Oxidation of the dithioles 5a and 6a led to S(2)-oxides (10a, 11a) and the corresponding S(2)-dioxides (10b, 11b) depending on reaction conditions. The thiosulfinate 10a was converted by a ring-opening/ring-closure reaction sequence to the bicyclic sulfinamide 12. The oxidative addition reactions of [Pt(η²-C₂H₄) (PPh₃)₂] (14) with the disulfides 5a and 13 led to the dithiolatoplatinum(II) complexes 15 and 16, respectively. Complex 16 was characterized structurally. The sulfenato-thiolato complex 17 was synthesized via reaction of 14 with the thiosulfinate 10a. The thiosulfonato Pt¹¹ complex 18 was prepared by an oxidative insertion of Pt⁰ into the C-S bond of the corresponding thiosulfonate 10b. Furthermore, complex 18 was characterized by single-crystal X-ray-diffraction studies.

Full text of DOI:10.1002/hlca.200290022

Helvetica Chimica Acta Vol. 85 (2002)
4453
Synthesis and Reactions of New Dithiolopyrroles1)2)
by Hans-Dietrich Stachel*a), Eduard Eckla), Elisabeth Immerz-Winklera), Christine Kreinera),
Wolfgang Weigand*b), Christian Roblb), Ralf W¸nschc), Stefan Dickc), and Norbert Drescherc)
a) Department Pharmazie/Zentrum f¸r Pharmaforschung, Universit‰t M¸nchen, Butenandtstr. 7, D-81377
M¸nchen (e-mail: hdsta@cup.uni-muenchen.de)
b) Institut f¸r Anorganische und Analytische Chemie, Friedrich-Schiller-Universit‰t Jena, August-Bebel-
Strasse 2, D-07743 Jena (fax: ‡ 493641948102; e-mail: wolfgang.weigand@uni-jena.de)
c) Department Chemie, Universit‰t M¸nchen, Butenandtstr. 9, D-81377 M¸nchen
Dedicated to Professor Dieter Seebach on the occasion of his 65th birthday
The title compounds were prepared starting from pyrrolinone 4. Nucleophilic-displacement and ring-
closure reactions yielded the dithiolopyrrole 5a, which formed salts with electrophiles (7, 8) as well as with bases.
The crystal structure of 5a was determined. Oxidation of the dithioles 5a and 6a led to S(2)-oxides (10a, 11a)
and the corresponding S(2)-dioxides (10b, 11b) depending on reaction conditions. The thiosulfinate 10a was
converted by a ring-opening/ring-closure reaction sequence to the bicyclic sulfinamide 12. The oxidative
addition reactions of [Pt(h2-C2H4) (PPh3)2] (14) with the disulfides 5a and 13 led to the dithiolatoplatinum(II)
complexes 15 and 16, respectively. Complex 16 was characterized structurally. The sulfenato-thiolato complex 17
was synthesized via reaction of 14 with the thiosulfinate 10a. The thiosulfonato PtII complex 18 was prepared by
an oxidative insertion of Pt0 into the CÀS bond of the corresponding thiosulfonate 10b. Furthermore, complex
18 was characterized by single-crystal X-ray-diffraction studies.
Introduction. Bicyclic dithioles of type 1 represent a highly stable kind of cyclic
disulfides due to their marked resonance [1]. Several natural substances belong to this
type. They were collectively named holothins and pyrrothins, this designation being
owed to the long-known antibiotics holomycin (2, R ˆ H) and thiolutin (2, R ˆ Me) [2].
Groups of holothins with longer side chains are the xenorhabdins [3], the marinols [4],
and other substances with potential value in therapy [5]. Recently, we reported the
synthesis and chemistry of differently substituted 1,2-dithiolopyrrolones of general
formula 3 [1][6][7]. Some of these compounds exhibited pharmacologically valuable
activities [8]. Supposedly, S-oxides of the respective dithiolopyrrolones play a decisive
role in the physiological activity [1]. It was shown that pyrrothins and other 1,2-
dithiolopyrroles bearing no substituents in the sulfur ring form highly reactive
carbenoid anions, which also may be intermediates in physiological actions [7].
To further investigate the chemical as well as the physiological properties of this
type of heterocycle, we have synthesized the phenyl substituted dithiolopyrrolones 3,
which we assumed to be more stable against alkali.
1
)
)
Fused 1,2-Dithioles, Part VI.
Metal complexes of functionalized sulfur-containing ligands, Part XVIII.
2

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R
R
S
S
S
S
O
O
N
R
N
R
R
R
1
COOMe
O
NHAc
O
S
S
S
S
N
N
R
Ph
R
2
3
Results and Discussion. The synthesis started from the known lactam 4 [9]. Upon
reaction with Na2S, nucleophilic displacement first of the MeO group and then of Br
occurred to yield a red dithiolate. The salt could not be isolated as an analytically pure
substance because of its ready oxidation by O2 in air. After completing the oxidation
with oxidants like I2 or H2O2, the dithiole 5a was obtained in good yield. The disulfide
bond of 5a was reduced with NaBH4 to the red dithiolate, which, upon re-oxidation,
gave back 5a quantitatively.
The molecular structure of 5a (Fig. 1) shows that the molecule is planar, as
anticipated; selected bond lengths and angles are given in Table 1. The Ph substituent is
out of plane with an angle of 31.58. The bond lengths of the heterocyclic C-atoms
distinctly alternate between double and single bonds. However, the formal double

Helvetica Chimica Acta Vol. 85 (2002)
4455
bonds between C(1)ÀC(2) and C(3)ÀC(4) are extended to 136 137 pm and the single
bond between C(2)ÀC(3) is shortened to 143.7(7) pm. The distance between S(1) and
S(2) was in the usual range for cyclic disulfides with 208.3(2) pm [10], but the
S(2)ÀC(3) bond (170.9(4) pm) is considerably shorter than the S(1)ÀC(1) bond
(175.6(5) pm). The usual CÀS distance was given as 174 pm [11].
Fig. 1. Molecular structure of 5a in the crystal
Table 1. Selected Bond Distances [pm] and Bond Angles [8] of 5a. For atom numbering, see Fig. 1.
Bond distances
S(1)ÀS(2)
S(1)ÀC(1)
S(2)ÀC(3)
C(1)ÀC(2)
C(2)ÀC(3)
208.3(2)
175.6(5)
170.9(4)
136.0(5)
143.7(7)
C(3)ÀC(4)
C(2)ÀN
137.2(5)
138.0(5)
139.7(6)
147.0(7)
C(5)ÀN
C(4)ÀC(5)
Bond angles
C(1)ÀS(1)ÀS(2)
C(3)ÀS(2)ÀS(1)
S(2)ÀC(3)ÀC(2)
C(1)ÀC(2)ÀC(3)
96.7(2)
94.0(2)
116.4(3)
119.4(4)
C(2)ÀC(3)ÀC(4)
C(2)ÀNÀC(5)
NÀC(5)ÀC(4)
C(3)ÀC(4)ÀC(5)
110.2(4)
110.9(4)
106.0(3)
106.6(4)
Due to considerable NH acidity, compound 5a formed a sparingly soluble
potassium salt in MeOH, which reacted with MeI to give the N-methylated compound
6a. The stability of both 5a and 6a even toward strong alkali opened the possibity to
saponify the ester groups to give the carboxylic acids 5b/6b. The acids decarboxylated in
the presence of copper in quinoline at 1508 forming the dithiolopyrrolones 5c/6c, which
are capable of electrophilic substitutions at C(6). Thus, HNO2 gave the green nitroso
derivatives 5d/6d, which also could be obtained directly from the acids 5b/6b upon
heating with NaNO2 to 408. Compounds 5d/6d were reduced with NaBH4 to give the
amines 5e/6e in good yields. The acetylated derivatives 5f and 6f are new pyrrothins
and can be called 3-phenylholomycin or 3-phenylthiolutin, respectively, because of the
structural similarity to the natural compounds 2.

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The high stability of the new dithioles allowed a number of textbook reactions to be
carried out smoothly. The carboxylic acid 6b was converted into the acid chloride 6g
and then into the azide 6h, which upon heating in Ac2O underwent the Curtius
rearrangement to give phenylthiolutin 6f. The dithiolopyrrolidone 6c was acetylated
under FriedelÀCrafts conditions to afford the ketone 6i. The Beckmann rearrangement
of oxime 6j in the presence of PCl5 took its course under preferential migration of the
heterocyclic residue to furnish 3-phenylthiolutin 6f.
On the other hand, the new dithiolopyrrolones showed low basicity. From
compound 5a and HClO4 in AcOH, the easily crystallized perchlorate 7 was obtained,
which hydrolyzed immediately upon contact with H2O. Analogously, reaction of 5a and
methyl fluorosulfonate gave the salt 8, the hydrolysis of which with NaHCO3 led to
imino ester 9. This compound may be regarded as a −dithia-azapentalene× or an −aza-
pseudoazulene×3) [12] and was also obtained by reaction of 5a and CH2N2 in nearly
quantitative yield. The preferential O-methylation of carboxylic acid amides with
CH2N2 is usually interpreted as a hint of the weakened double-bond character of the
carbonyl group due to resonance [13].
The pyrrothines 5a/6a were oxidized with 3-chloroperbenzoic acid (mCPBA) or
with H2O2 in AcOH at ambient temperature stepwise to give first the poorly soluble
yellow thiosulfinates 10a/11a and then the orange colored thiosulfonates 10b/11b. It
proved difficult to obtain the thiosulfinates 10a or 11a completely free of the
corresponding thiosulfonates because, noteworthily, their Rf values hardly differed
from each other.
In principle, the oxidation of compounds 5a/6a could have taken place at S(1) or at
S(2). Both pathways have been observed with other bicyclic dithioles [1]. Proof of the
correct structure of the S(2)-oxide 10a was given by a reaction formerly referred to as
−S/N-exchange reaction× of cyclic thiosulfinates [1]. As expected, the reaction of
thiosulfinate 10a with MeNH2 in the presence of I2 yielded the isothiazolopyrrolone S-
oxide 12 (Scheme), which is already known and was prepared by an unambiguous
synthesis [14]. Likewise, compound 11a is a S(2)-oxide because it was obtained by N-
methylation of 10a. From the structures of the monoxides 10a/11a, it cannot be
concluded that the dioxides 10b/11b also are S(2)-oxides. It is known that the oxidation
of thiosulfinates to thiosulfonates by electrophilic oxidants may proceed via 1,2-
disulfoxides and their disproportionation [15]. This pathway of oxidation is hindered by
use of a nucleophilic oxidant like NaIO4 [16]. Since oxidation of the monoxides 10a/11a
with this reagent likewise afforded the dioxides 10b/11b, their identification as S(2)-
dioxides gained credence. The structure of 10b was finally secured by X-ray-diffraction
analysis [17].
The thiosulfinates 10a/11a were deoxygenated either by NaBH4 or by 1,2-
dimethylhydrazine [1] to give the dithioles 5a/6a. The yellow sulfoxides turn red in
day light, most likely due to disproportionation. The propensity of thiosulfinates to
disproportionation is well-known from other pyrrothin S-oxides [1] as well as from
‡
‡
acyclic representatives [18]. MS of the thiosulfinates showed M as well as [M À O]
peaks. MS of the dioxides 10b/11b gave evidence of another route of decomposition by
[M À SO2] fragments beside the molecular-ion peaks. The most prominent peak in the
‡
3
)
The term −pseudoazulene× was frequently used for cyclopenta[1,2]dithioles.

Helvetica Chimica Acta Vol. 85 (2002)
4457
Scheme
Me
N
COOMe
O
COOMe
O
S
X
10a
OS
Ph
N
R
N
H
Ph
10a R = H, X = SO
b R = H, X = SO2
11a R = Me, X = SO
12
b R = Me, X = SO2
COOEt
O
S
S
N
Me
MeOOC
13
MS fragmentation of all the above dithioles and their S-oxides was that of the
thiobenzoyl ion (m/z 121).
The chemical behavior of the S-oxides 10/11 is characterized by a bicyclic system
that is less stable against alkali in comparison with the dithioles 5/6. As already
mentioned, the S-oxide 10a rapidly suffered cleavage of the dithiolo ring with an amine,
while the dithiolopyrrole 5a was completely stable under these conditions. The aqueous
solutions of the potassium salts of S-oxides 10a or 11a decomposed quickly at room
temperature so that, upon acidification after 30 min, no trace of the starting compound
was detectable by thin layer chromatography (TLC). Contrariwise, the dithiolopyrrole
5a could be recovered unchanged from the aqueous solutions of its potassium salt after
3 d. The oxides 10a/b were converted by CH2N2 to the N-methylated derivatives 11a/b
exclusively, while the reaction of 5a with CH2N2 afforded the imino ether 9 solely.
The lesser mesomeric stabilization of the oxidized bicyclic systems 10/11 compared
to the basis systems 5a/6a can also be seen in the IR and UV spectra. Comparing the IR
spectrum of 5a with the spectra of the monoxides 10a/11a and the dioxides 10b/11b, the
CˆO absorption bands of all oxides were shifted toward higher wavelenghts,
demonstrating lowered resonance participation of the ester groups in the oxides. The
longest-wave UV-absorption maxima of the oxides did not show the −negative
solvatochromy× observed in solutions of the dithiole 5a in solvents of different
polarities. Such solvatochromy was said to go along with marked electron delocaliza-
tion [19].
In preliminary work [20 22], it was shown that cyclic thiosulfinates react readily
with Pt0 complexes [Pt(h2-C2H4)(PR3)2] via insertion of Pt0 into the SÀS(O) bond, to
give chelate complexes containing sulfenato-thiolato compounds. Thus, we studied the
oxidative addition of Pt0 compounds with the thiosulfinate 10a. We also extended the
study of reactivity of [Pt(h2-C2H4)(PPh3)2] (14) toward the disulfides 5a and 13,
respectively, as well as the thiosulfonate 10b.

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Reaction of a mixture of 14 and 5a in toluene at room temperature under N2
afforded the dithiolato complex 15 after workup. The analogous complex 16 was also
formed via insertion of Pt0 into the SÀS bond of 13.
Complex 15 and 16 were characterized by NMR spectroscopy and 16 additionally
by X-ray structure determination. The 31P-NMR spectrum of 15 and 16, respectively,
showed the characteristic pattern of an AB spin system expected for two chemical
nonequivalent cis phosphines on a square-planar dithiolatoplatinum(II) complex, with
resonances at d 21.08, 22.49 ppm (1J(Pt,P) ˆ 2927, 2939 Hz, 2J(P,P) ˆ 31.5 Hz; 15) and d
2
22.48, 22.76 ppm (1J(Pt,P) ˆ 2956, 3012 Hz, J(PÀP) ˆ 29.8 Hz; 16), respectively. In
the 13C-NMR spectrum of 15, the signals assigned to the quaternary C-atoms bound to
the S-atoms are at d 150.8 ppm (3J(C,P) ˆ 5.6 Hz) and 141.2 ppm (3J(C,P) ˆ 9.2 Hz).
The molecular structure of the dithiolato complex 16 is shown in Fig. 2;
selected bond lengths and angles are given in Table 2. The six-membered cyclic
dithiolato platinum(II) complex is distorted from planar, with a dihedral angle
of 19.98 between the plane S(1)ÀPtÀS(2) and the mean plane through
S(1)ÀC(37)ÀC(40)ÀC(41)ÀS(2). The twist angle in the coordination plane between
the PtP2 and the PtS2 units is 12.58. Key bond lengths are PtÀS(1) 229.6(2) pm, PtÀS(2)
230.6(2) pm, PtÀP(1) 229.2(2) pm, and PtÀP(2) 231.5(2) pm, which are very similar to
those seen with six-membered cyclic dithiolato complexes [23].
By a procedure similar to that used for the disulfides 5a and 13 [1], the oxidative
addition of the thiosulfinate 10a to 14 yielded the complex 17 after workup. In the 31P-
NMR spectrum the typical AB pattern for a sulfenato-thiolatoplatinum(II) complex
could be observed [22]: it consists of two doublets at d 19.72 ppm (1J(Pt,P) ˆ 2280 Hz,
2J(P,P) ˆ 30.5 Hz), for P trans to S(O), and d 22.04 ppm [1J(Pt,P) ˆ 3435 Hz, 2J(P,P) ˆ
30.5 Hz), for P trans to S. This was in accordance with our previous finding that the
sulfenato group exhibits a stronger trans influence than the thiolato group [24]. In the
13C-NMR spectrum, the signal at 162 ppm is assigned to the C-atom directly bonded to
the mono-oxidized S-atom; the resonance signal of this C-atom is shifted downfield by

Helvetica Chimica Acta Vol. 85 (2002)
4459
Fig. 2. Molecular structure of 16 in the crystal
Table 2. Selected Bond Distances [pm] and Bond Angles [8] of 16. For atom numbering, see Fig. 2.
Bond distances
PtÀS(1)
PtÀS(2)
PtÀP(1)
PtÀP(2)
229.6(2)
230.6(2)
229.2(2)
231.5(2)
S(1)ÀC(37)
S(2)ÀC(41)
C(37)ÀC(40)
C(40)ÀC(41)
172.6(6)
167.0(6)
133.3(8)
145.1(9)
Bond angles
S(1)ÀPtÀS(2)
P(1)ÀPtÀP(2)
P(1)ÀPtÀS(1)
94.99(6)
95.13(6)
88.85(6)
P(2)ÀPtÀS(2)
P(1)ÀPtÀS(2)
P(2)ÀPtÀS(1)
82.46(6)
171.51(7)
169.11(6)
11 ppm compared with that of the respective C-atom of the dithiolato complex 15. The
IR spectrum of 17 exhibits a characteristic nÄ(SO) band at 999 cmÀ1, which is in
agreement with these absorptions observed for other sulfenato complexes [22]. The
nÄ(SO) band in complex 17 is shifted 70 cmÀ1 to lower wavenumbers compared to that of
the corresponding thiosulfinate 10a.
In contrast, 14 reacted with the thiosulfonate 10b via CÀS cleavage in toluene at
room temperature, giving the thiosulfonato complex 18 as a result of the insertion of
Pt(0) into the CÀS bond. Interestingly, while organic thiosulfonates R'ÀSÀSO2ÀR are
known, metal complexes containing the anion RÀSO2ÀSÀ as ligands are very rare and
limited to few Fe(II) as well as Ru(II) complexes like [M(SÀSO2R)(C)L2] (M ˆ Fe,
Ru) [25]. The RÀSO2ÀSÀ ligands are isomeric with those in trans-[Pt(phthalimido)-

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Helvetica Chimica Acta Vol. 85 (2002)
(SO2ÀSÀR)](PPh3)2 [26]. Complex 18 was characterized by spectroscopic methods
and by X-ray structure determination (Fig. 3). Both methods confirmed that insertion
of Pt(0) takes place selectively into the CÀS bond in the case of thiosulfonate 10b,
yielding the Pt bonded thiosulfonato complex. The 31P-NMR spectrum of 18 exhibited
the coupling pattern of an AB spin system; it confirmed that the trans influence of the
C-donor atom is stronger than that of the S-donor atom: d 7.47 (1J(Pt,P) ˆ 2054 Hz,
2J(P,P) ˆ 20.7 Hz; P trans to C) and d 12.56 ppm (1J(Pt,P) ˆ 3724 Hz, 2J(P,P) ˆ 20.7 Hz;
P trans to S) [27]. The significant bands in the IR spectrum of complex 18 are those
associated with the thiosulfonyl group, which shows both symmetric (1273 cmÀ1) and
asymmetric modes (1094 cmÀ1), respectively [25]. These bands are shifted to lower
wavenumbers compared to those of the parent thiosulfonate 10b (1342, 1145 cmÀ1) due
to the electron-donating effect of the electropositive Pt-atom.
Fig. 3. Molecular structure of 18 in the crystal. The phenyl rings at the P-atoms have been omitted for clarity.
The molecular structure of 18 is shown in Fig. 3, selected bond lengths and angles
are given in Table 3. The Pt coordination plane shows strong distortion from square
planarity with a P(1)ÀPtÀS(2)/S(2)ÀPtÀC(3) dihedral angle of 22.98. The distortion,
prompted by the steric bulk of the Ph3P ligands and the bite of the C,S-ligand, is
reflected in the P(1)ÀPtÀP(2) and C(3)ÀPtÀS(2) bond angles of 102.9(1)8 and
86.9(2)8, respectively. The PtÀP(1) and PtÀP(2) bond lengths are 235.8(2) and
227.3(2) pm. This confirms that the s-bonded vinylic C-atom has a higher trans
influence than the S-donor atom. The PtÀC(3) bond length of 204.6(7) pm is similar to
that observed in six-membered thiaplatina cycles [27]. The SÀS(O)2 distance in
complex 18 is about 9.5 pm smaller than that in the corresponding compound 10b [17]
and comparable to those in other known thiosulfonato complexes [25].

Helvetica Chimica Acta Vol. 85 (2002)
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Table 3. Selected Bond Distances [pm] and Bond Angles [8] of 18. For atom numbering, see Fig. 3.
Bond distances
PtÀP(1)
PtÀP(2)
PtÀS(2)
PtÀC(3)
S(1)ÀS(2)
235.8(2)
227.3(2)
236.2(2)
204.6(7)
203.4(2)
S(1)ÀO(4)
S(1)ÀO(5)
S(1)ÀC(1)
C(1)ÀC(2)
C(2)ÀC(3)
143.4(4)
144.2(5)
178.1(7)
132.4(8)
153.7(8)
Bond angles
S(2)ÀPtÀC(3)
P(1)ÀPtÀP(2)
P(1)ÀPtÀS(2)
P(2)ÀPtÀC(3)
P(1)ÀPtÀC(3)
86.9(2)
102.9(1)
86.3(1)
88.7(2)
162.4(2)
P(2)ÀPtÀS(2)
160.6(1)
107.3(2)
112.5(2)
115.5(3)
107.2(2)
S(2)ÀS(1)ÀO(4)
S(2)ÀS(1)ÀO(5)
O(4)ÀS(1)ÀO(5)
S(2)ÀS(1)ÀC(1)
Experimental Part
General. M .p.:Gallenkamp melting-point apparatus; uncorrected. IR spectra: Perkin-Elmer PARAGON-
1000; KBr pellets; nÄ in cmÀ1. UV/VIS spectra: Kontron Uvikon-810 Anacomp-220 or Perkin-Elmer Lambda-20;
1
lmax in nm (log e) in MeOH soln., if not stated otherwise. H-NMR spectra: JEOL GSX-400; d in ppm rel. to
Me4Si as internal standard, J in Hz, solvent (D6)DMSO, if not indicated otherwise. MS: Hewlett-Packard 5989A,
70 eV. Flash chromatography (FC): Flash column 250 ml (Baker) with silica gel 0.040 0.063 mm (Merck).
Elemental analysis: Heraeus CHNO-Rapid Analyzer or carried out by I. Beetz, Mikroanalytisches Laborato-
rium, Kronach, Germany.
General Procedure A (GP A). Synthesis of Thiosulfinates from Dithioles. A soln. of 0.27 g (1.1 mmol) of
mCPBA (70%) in CH2Cl2 (10 ml) was added to a stirred soln. of the dithiole (2 mmol) in CH2Cl2 (15 ml), and
the mixture was left for 5 h at r.t. The soln. was washed with sat. aq. NaHCO3 soln. (10 ml) and dried (Na2SO4).
The solvent was removed in vacuo, and the residue (mainly monoxide, traces of dioxide) was crystallized.
General Procedure B (GP B). Synthesis of Thiosulfonates from Dithioles. A soln. of 0.52 g (2.1 mmol) of
mCPBA (70%) in CH2Cl2 (10 ml) was added to a stirred soln. of the dithiole (1 mmol) in CH2Cl2 (15 ml), and
the mixture was left at r.t. for the time given. The soln. was washed with sat. aq. NaHCO3 soln. (10 ml) and dried
(Na2SO4). The solvent was removed in vacuo, and the residue was recrystallized.
General Procedure C (GP C). Reduction of Thiosulfinates with 1,2-Dimethylhydrazine. A soln. of the
dithiole S-oxide (1 mmol) in CH2Cl2 (10 ml) was added to
a stirred soln. of 1.8 g (15 mmol) 1,2-
dimethylhydrazine dihydrochloride and 6.3 g (30 mmol) 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in anh.
CH2Cl2 (15 ml). After stirring for 2 h at r.t., the soln. was washed repeatedly with 1n H2SO4 and, at last, with
H2O and dried (Na2SO4). The solvent was removed in vacuo, and the residue was recrystallized.
Methyl 4,5-Dihydro-5-oxo-3-phenyl[1,2]dithiolo[4,3-b]pyrrole-6-carboxylate (5a).
(22 mmol) of Na2S ¥ 9 H2O in MeOH (30 ml) was added to a stirred suspension of 3.38 g (10 mmol) of methyl
5-[bromo(phenyl)methylidene]-2,5-dihydro-4-methoxy-2-oxo-1H-pyrrole-3-carboxylate (4) [9] in eOH
A soln. of 5.28 g
M
(15 ml). The red soln. obtained was heated to reflux for 1 h. After cooling, the resulting red precipitate (of
the dithiolate) was isolated, the salt dissolved in the necessary amount of H2O and stirred for 2 h after addition
of 2 ml of aq. soln. (30%) H2O2. The yellow precipitate was isolated and recrystallized. 38% of 5a. Yellow
crystals. M.p. 246 2488 (MeOH). UV: 398 (4.213), 265 (3.991), 217 (4.028); pH 10: 413 (4.308), 239 (3.921),
216 (4.020). IR: 3100, 3000, 2970, 1728s, 1685s, 1660s. 1H-NMR: 11.16 (s, 1 H); 7.66 (m, 5 H); 3.81 (s, 3 H). M S:
‡
291 (M ), 121. Anal. calc. for C13H9NO3S2 (291.35): C 53.59, H 3.11, N 4.81; found: C 53.57, H 3.19, N 4.76.
4,5-Dihydro-5-oxo-3-phenyl[1,2]dithiolo[4,3-b]pyrrole-6-carboxylic Acid (5b). A soln. of 1.45 g (5 mmol)
of 5a in MeOH (20 ml) was heated with 7n KOH (10 ml) at reflux temp. for 3 h. The precipitated salt was
collected, and its aq. soln. was acidified with dil. HCl while cooling. The yellow precipitate was isolated and
recrystallized. 64% of 5b. Yellow-green powder. M.p. 268 2708 (AcOH). UV: 396 (4.201), 267 (3.860), 217
(3.912). IR: 3400 (br.), 3100, 2940, 1720, 1640. 1H-NMR: 12.38 (s, 1 H); 11.18 (s, 1 H); 7.62 (m, 5 H). MS: 278
‡
([M ‡ 1] ), 122. Anal. calc. for C12H7NO3S2 (277.32): C 51.97, H 2.54, N 5.05, S 23.13; found: C 51.96, H 2.78,
N 5.07, S 22.93.

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Helvetica Chimica Acta Vol. 85 (2002)
3-Phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (5c). A suspension of 1.11 g (4 mmol) of 5b in quinoline
(4 ml) was heated with a small amount of powdered Cu shortly to boiling. After the evolution of CO2 had
ceased, the mixture was cooled, diluted with CH2Cl2 (20 ml), filtered, and concentrated in vacuo. Upon addition
of Et2O, the product started to crystallize. 55% of 5c. Orange crystals. M.p. 215 2168 (Et2O). UV: 376 (4.196),
‡
261 (3.915). IR: 3130, 2990, 1670. 1H-NMR: 10.80 (s, 1 H); 7.70 7.42 (m, 5 H); 5.95 (s, 1 H). MS: 233 (M ), 121.
Anal. calc. for C11H7NOS2 (233.31): C 56.63, H 3.02, N 6.00, S 27.49; found: C 57.63, H 3.39, N 6.56, S 27.89.
6-Nitroso-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (5d). An aq. soln. of 0.70 g (10 mmol) of NaNO2
was added to a suspension of 0.56 g (2 mmol) of 5c in AcOH (5 ml). Upon heating to 408 for 1 h, the product
started to precipitate. 73% of 5d. Dark green crystals. M.p. 238 2408 (AcOH). UV: 485 (3.649), 394 (4.015),
338 (3.861), 279 (4.213). IR: 3330, 2940, 1715, 1660, 1635. 1H-NMR: 11.52 (s, 1 H); 7.97 7.50 (m, 5 H). MS: 262
‡
(M ), 121. Anal. calc. for C11H6N2O2S2 (262.31): C 50.37, H 2.31, N 10.68, S 24.45; found: C 50.47, H 2.38, N 9.98,
S 23.28.
6-Amino-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (5e). A soln. of 0.26 g (1 mmol) of 5d and 0.38 g
(10 mmol) of NaBH4 in MeOH (5 ml) was stirred for 15 min. The precipitate was isolated and recrystallized.
56% of 5e. Orange crystals. M.p. 2058 (MeOH). Dark red precipitate with Ehrlich×s reagent. UV: 416 (4.039),
320 (3.817), 275 (4.137). IR: 3380, 3260, 3120, 2960, 1690. 1H-NMR: 7.58 7.30 (m, 5 H); 4.30 (m, 3 H). MS: 248
‡
(M ), 121. Anal. calc. for C11H8N2OS2 (248.33): C 53.20, H 3.25, N 11.28, S 25.83; found: C 53.05, H 3.38,
N 11.11, S 25.71.
N-(4,5-Dihydro-5-oxo-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-6-yl)acetamide (3-Phenylholomycin, 5f). A soln.
of 0.25 g (1 mmol) of 5e in Ac2O (3 ml) was left for 30 min at r.t. The precipitate was collected and
recrystallized. 68% of 5f. Red-brown crystals. M.p. 2598 (MeOH/CH2Cl2 1:1). UV: 415 (4.141), 322 (3.829), 259
(4.237). IR: 3230, 3160, 3020, 1650, 1635, 1600. 1H-NMR: 11.00 (s, 1 H); 9.97 (s, 1 H); 7.53 (m, 5 H); 2.07
‡
(s, 3 H). MS: 290 (M ), 121. Anal. calc. for C13H10N2O2S2 (290.36): C 53.77, H 3.47, N 9.65, S 22.09; found:
C 53.66, H 3.55, N 9.64, S 22.00.
Methyl 4,5-Dihydro-4-methyl-5-oxo-3-phenyl[1,2]dithiolo[4,3-b]pyrrole-6-carboxylate (6a). To a soln. of
0.29 g (1 mmol) of 5a in anh. DMF (5 ml) were added 0.033 mg (1.1 mmol) of NaH (80%). The mixture was
first stirred for 1 h at r.t. and then for another 2 h after addition of MeI (2 ml). The mixture was diluted with
CH2Cl2 (30 ml) and extracted three times with H2O. The org. layer was dried (Na2SO4) and the solvent removed
in vacuo. The residue crystallized after addition of a small amount of MeOH. 65% of 6a. Yellow crystals. M.p.
181 1828 (MeOH). UV: 392 (4.218), 218 (4.018). IR: 3040, 2980, 2940, 1725, 1680, 1610. 1H-NMR: 7.62
‡
(s, 5 H); 3.80 (s, 3 H); 2.88 (s, 3 H). MS: 305 (M ), 121. Anal. calc. for C14H11NO3S2 (305.37): C 55.06, H 3.63,
N 4.59; found: C 55.18, H 3.63, N 4.54.
4,5-Dihydro-4-methyl-5-oxo-3-phenyl[1,2]dithiolo[4,3-b]pyrrole-6-carboxylic Acid (6b). As described for
5b, with 1.53 g (5 mmol) of 6a and 4n KOH (10 ml). The saponification was complete after 1 h. 60% of 6b.
Beige powder. M.p. 230 2328 (AcOH). UV: 393 (4.118), 219 (3.981). IR: 3450 (br.), 3000 (br.), 1710, 1660,
‡
1630. 1H-NMR: 12.2 (br. s, 1 H); 7.6 (s, 5 H); 2.90 (s, 3 H). MS: 291 (M ), 121. Anal. calc. for C13H9NO3S2
(291.35): C 53.59, H 3.11, N 4.81; found: C 53.72, H 2.98, N 4.93.
4-Methyl-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (6c). As described for 5c, with 0.87 g (3 mmol) of
6b. The residue was purified by FC (1. petrol ether, 2. Et2O). The second fraction was collected, and the solvent
was removed in vacuo. 51% of 6c. Orange crystals. M.p. 137 1388 (Et2O). UV: 366 (4.271), 244 (sh), 219
(4.018). IR: 3100, 2920, 1655. 1H-NMR: 7.56 (s, 5 H); 6.03 (s, 1 H); 2.86 (s, 3 H). 1H-NMR (CDCl3): 7.48
(s, 5 H); 5.97 (s, 1 H); 3.00 (s, 3 H). 13C-NMR (CDCl3): 173.0 (C(5)); 156.6 (C(6a)); 133.1 (C(3a)); 130.3 128.0
‡
(arom. C); 125.5 (C(3)); 103.7 (C(6)); 28.1 (Me). MS: 247 (M ), 121. Anal. calc. for C12H9NOS2 (247.34):
C 58.27, H 3.67, N 5.66, S25.93; found: C 58.21, H 3.75, N 5.68, S 25.76.
4-Methyl-6-nitroso-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (6d). As described for 5d, with 0.58 g
(2 mmol) of 6c. 85% of 6d. Green crystals. M.p. 237 2398 (AcOH). UV: 476 (3.693), 394 (4.121), 336 (3.866),
1
‡
280 (4.013). IR: 3060, 2950, 1700, 1580. H-NMR: 7.93 (s, 5 H); 3.10 (s, 3 H). MS: 275 ([M À 1] ), 121. Anal.
calc. for C12H8N2O2S2 (276.34): C 52.16, H 2.92, N 10.14, S 23.21; found: C 51.90, H 2.74, N 9.89, S 22.94.
6-Amino-4-methyl-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (6e). As described for 5e, with 0.28 g
(1 mmol) of 6d. 48% of 6e. Red crystals. M.p. 164 1668 (MeOH). UV: 392 (4.193), 309 (3.927), 241 (4.136).
IR: 3410, 3310, 2930, 1665, 1585. 1H-NMR: 7.47 (s, 5 H); 2.83 (s, 3 H). MS: 262 (M ), 121. Anal. calc. for
‡
C12H10N2OS2 (262.35): C 54.94, H 3.84, N 10.68, S 24.44; found: C 55.19, H 4.11, N 10.84, S 24.54.
N-(4,5-Dihydro-4-methyl-5-oxo-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-6-yl)acetamide (3-Phenylthiolutin, 6f).
Procedure 1. As described for 5f, with 0.26 g (1 mmol) of 6e. 95% of 6f.
Procedure 2. A soln. of 0.30 g (1.5 mmol) of PCl5 in benzene (10 ml) was added to a stirred soln. of 0.30 mg
(1 mmol) of 6j in benzene (10 ml). After 15 min, the soln. was washed several times with sat. aq. NaHCO3 soln.

Helvetica Chimica Acta Vol. 85 (2002)
4463
until neutral reaction. The org. phase was dried (Na2SO4), the solvent was removed in vacuo, and the residue
was recrystallized. 63% of 6f.
Procedure 3. A soln. of 0.33 mg (1 mmol) of 6h in Ac2O (5 ml) was heated to 1008 for 1.5 h, whereupon the
product precipitated. 46% of 6f.
Data of 6f: Yellow crystals. M.p. 258 2618 (EtOH). UV: 394 (4.091), 314 (3.919), 252 (4.273). IR: 3260,
‡
3040, 2920, 1670, 1645, 1600. 1H-NMR: 9.98 (s, 1 H); 7.55 (s, 5 H); 2.87 (s, 3 H); 2.07 (s, 3 H). MS: 304 (M ), 121.
Anal. calc. for C14H12N2O2S2 (304.39): C 55.24, H 3.97, N 9.20, S 21.07; found: C 55.24, H 3.90, N 9.05, S 20.93.
4,5-Dihydro-4-methyl-5-oxo-3-phenyl[1,2]dithiolo[4,3-b]pyrrole-6-carbonyl Chloride (6g). A soln. of 1.45 g
(5 mmol) of 6b in SOCl2 (6 ml) was heated to reflux (hood) until the gas evolution ceased. The volatile
components were removed in vacuo at 408, and the residue was washed several times with Et2O. 60% of 6g.
‡
Green powder. M.p. 189 1918. UV: 386 (4.198), 220 (4.023). IR: 2940, 1780, 1765, 1660. MS: 282 ([M À 28] ),
121. Anal. calc. for C13H8ClNO2S2 (309.79): C 50.40, H 2.60, N 4.52, S 20.70; found: C 50.21, H 2.55, N 4.38,
S 20.50.
6-(Azidocarbonyl)-4-methyl-3-penyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (6h). A soln. of 0.071 g (1 mmol)
of NaN3 in 1 ml H2O was added dropwise to a stirred soln. of 0.31 g (1 mmol) of 6g in acetone (3 ml). The
product precipitated and was recrystallized. 72% of 6h. Yellow crystals. M.p. 133 1348 (acetone/H2O 1:1). UV:
415 (4.298), 248 (4.102). IR: 3050, 2940, 2130, 1705, 1670, 1645, 1600. 1H-NMR: 7.67 (s, 5 H); 2.93 (s, 3 H). M S:
‡
288 ([M À 28] ), 121. Anal. calc. for C13H8N4O2S2 (316.36): C 49.36, H 2.55, N 17.71, S 20.27; found: C 49.42,
H 2.62, N 17.66, S 20.13.
6-Acetyl-4-methyl-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (6i). To a suspension of 0.14 g (1 mmol) of
powdered anh. AlCl3 in anh. 1,2-dichloroethane (5 ml) was added with stirring 0.08 g (1 mmol) of AcCl and
0.24 g (0.95 mmol) of 6c. After further stirring with exclusion of moisture for 2 h at r.t., the soln. was poured into
ice water containing conc. HCl (5 ml), and the mixture was extracted three times with CH2Cl2. The combined
org. layers were washed with sat. NaHCO3 soln. and H2O and dried (Na2SO4). The solvent was removed in
vacuo, and the residue was recrystallized. 40% of 6i. Orange crystals. M.p. 178 1808 (MeOH). UV: 413 (4.115),
263 (3.761), 225 (4.288). IR: 3050, 2940, 1665, 1600. 1H-NMR (CDCl3): 7.50 (s, 5 H); 3.05 (s, 3 H); 2.60 (s, 3 H).
‡
MS: 289 (M ), 121. Anal. calc. for C14H11NO2S2 (289.38): C 58.11, H 3.83, N 4.84, S 22.16; found: C 58.15,
H 3.88, N 4.93, S 22.02.
6-[(1-Hydroxyimino)ethyl]-4-methyl-3-phenyl[1,2]dithiolo[4,3-b]pyrrol-5(4H)-one (6j). A soln. of 0.082 g
(1 mmol) of AcONa and 0.070 mg (1 mmol) of hydroxylammonium chloride in 2 ml H2O was added to a stirred
suspension of 0.15 g (0.5 mmol) of 6i in a mixture of DMSO and MeOH (2 ml each). The mixture was kept
over-night at 858. The product precipitated while cooling. 74% of 6j. Orange crystals. M.p. 230 2328 (MeOH).
UV: 412 (3.960), 344 (3.877), 258 (4.278). IR: 3260, 1645, 1600. 1H-NMR (CDCl3): 7.59 (s, 5 H); 3.07 (s, 3 H);
‡
2.47 (s, 3 H). MS: 304 (M ), 121. Anal. calc. for C14H12N2O2S4 (304.39): C 55.24, H 3.97, N 9.20, S 21.07; found:
C 54.74, H 3.97, N 9.02, S 21.01.
5-Hydroxy-6-(methoxycarbonyl)-3-phenyl-4H-[1,2]dithiolo[4,3-b]pyrrol-2-ium Perchlorate (7). Upon ad-
dition of 0.16 g (1.1 mmol) of HClO4 (70%) to a soln. of 0.29 g (1 mmol) of 5a in AcOH (5 ml), 7 precipitated
at once. The salt was washed once with AcOH and dried for 1 h in vacuo. 76% of 7. Yellowish crystals (AcOH).
M.p. 218 2208 (dec.). UV (HClO4): 368 (3.970), 285 (3.807), 243 (4.001). IR: 3340 (br.), 3240, 3040, 2920,
1
2830, 1710, 1660, 1590. H-NMR: 11.08 (s, 1 H); 7.55 (s, 5 H); 3.81 (s, 3 H).
5-Methoxy-6-(methoxycarbonyl)-3-phenyl-4H-[1,2]dithiolo[4,3-b]pyrrol-2-ium Fluorosulfonate (8). The
soln. of 0.29 g (1 mmol) of 5a and 1 ml (10 mmol) of methyl fluorosulfonate in anh. 1,2-dimethoxyethane (5 ml)
was heated at reflux for 15 min. While cooling, 8 precipitated quantitatively and was used immediately for the
synthesis of 9.
Methyl 5-Methoxy-3-phenyl[1,2]dithiolo[4,3-b]pyrrole-6-carboxylate (9). Procedure 1. Compound
8
(1 mmol) was stirred with sat. aq. NaHCO3 soln. (10 ml) and then extracted three times with CH2Cl2. The
combined org. layers were dried (Na2SO4), and the solvent was removed in vacuo. 79% of 9.
Procedure 2. An ethereal soln. of excessive CH2N2 was added to a stirred suspension of 0.30 g (1 mmol) of
5a in Et2O (10 ml). A clear soln. was obtained after stirring for 2 h. Removal of the volatile components gave 9
in nearly quantitative yield.
Data of 9: Yellow needles. M.p. 138 1398 (MeOH). UV: 381 (4.311), 293 (sh), 247 (3.872), 215 (4.165).
IR: 3040, 2990, 1717, 1670. 1H-NMR (CDCl3): 8.22 (mc, 2 H); 7.45 (mc, 3 H); 4.16 (s, 3 H); 3.86 (s, 3 H). MS: 305
‡
(M ), 121. Anal. calc. for C14H11NO3S2 (305.37): C 55.06, H 3.63, N 4.59, S 21.00; found: C 55.32, H 3.59, N 4.49,
S 21.03.
Methyl 4,5-Dihydro-2,5-dioxo-3-phenyl-2H-2l4-[1,2]dithiolo[4,3-b]pyrrole-6-carboxylate (10a). According
to GP A, with 0.58 g (2 mmol) of 5a. 46% of 10a. Faintly yellow crystals. M.p. 226 2288 (AcOH). UV: 329

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Helvetica Chimica Acta Vol. 85 (2002)
(4.210), 226 (4.120). IR: 3280, 3150, 3056, 2957, 1758, 1714, 1655, 1071. 1H-NMR: 11.30 (s, 1 H); 7.57 (m, 5 H);
‡
‡
3.83 (s, 3 H). MS: 307 (M ), 291 ([M À 16] ), 121. Anal. calc. for C13H9NO4S2 (307.35): C 50.80, H 2.95, N 4.56,
S 20.87; found: C 50.71, H 3.01, N 4.62, S 20.57.
Methyl 4,5-Dihydro-2,2,5-trioxo-3-phenyl-2 H-2l6-[1,2]dithiolo[4,3-b]pyrrole-6-carboxylate (10b). A soln.
of 1.45 g (5 mmol) of 5a and 3.92 g (20 mmol) of mCPBA (70%) in anh. 1,2-dimethoxyethane (30 ml) was
heated to reflux for 5 h. The soln. was worked up according to GP B. 42% of 10b. Orange crystals. M.p. 241
2438 (AcOH or MeOH). UV: 321 (4.122), 220 (3.902). IR: 3150, 3020, 2948, 1756, 1723, 1690, 1652, 1342, 1145.
‡
1H-NMR: 11.66 (s, 1 H); 7.63 (s, 5 H); 3.86 (s, 3 H). MS: 322 ([M À 1] ), 121. Anal. calc. for C13H9NO5S2
(323.35): C 48.29, H 2.81, N 4.33, S 19.83; found: C 48.17, H 2.73, N 4.44, S 20.05.
Methyl 4,5-Dihydro-4-methyl-2,5-dioxo-3-phenyl-2H-2l4-[1,2]dithiolo[4,3-b]pyrrole-6-carboxylate (11a).
Procedure 1. According to GP A, with 0.31 g (1 mmol) of 6a. 52% of 11a.
Procedure 2. As described for 6a, by N-methylation of 10a (0.31 g, 1 mmol). 40% of 11a.
Data of 11a: Faintly yellow crystals. M.p. 2118 (AcOH). UV: 316 (4.291), 220 (4.081). IR: 2950, 2920, 1740,
1655, 1580, 1070. 1H-NMR: 7.63 (s, 5 H); 3.86 (s, 3 H); 2.75 (s, 3 H). 13C-NMR (CDCl3): 167.2 (C(5)); 163.1
(COOMe); 161.3 (C(6a)); 139.5 (C(3a)); 131.0 128.6 (arom. C); 126.6 (C(3)); 113.1 (C(6)); 52.7 (MeO); 28.1
‡
‡
(MeN). MS: 321 (M ), 305 ([M À 16] ), 121. Anal. calc. for C14H11NO4S2 (321.37): C 52.32, H 3.45, N 4.36,
S 19.96; found: C 52.53, H 3.19, N 4.43, S 19.66.
Methyl 4,5-Dihydroxy-4-methyl-2,2,5-trioxo-3-phenyl-2H-2l6-[1,2]dithiolo[4,3-b]pyrrole-6-carboxylate
(11b). Procedure 1. According to GP B, with 0.31 g (1 mmol) of 6a. 63% of 11b.
Procedure 2. As described for 6a, by N-methylation of 10b (0.32 g, 1 mmol). 36% of 11b.
Data of 11b: Faintly yellow crystals. M.p. 232 2348 (MeOH). UV: 314 (4.188), 226 (4.003). IR: 3060, 2960,
1755, 1680, 1590, 1325, 1140. 1H-NMR (CDCl3): 7.60 (s, 5 H); 3.98 (s, 3 H); 2.90 (s, 3 H). 13C-NMR (CDCl3):
165.2 (C(5)); 162.5 (COOMe); 153.7 (C(6a)); 136.2 (C(3a)); 132.0 128.9 (arom. C); 123.6 (C(3)); 113.1
‡
(C(6)); 53.2 (MeO); 28.2 (MeN). MS: 337 (M ). Anal. calc. for C14H11NO5S2 (337.40): C 49.84, H 3.29, N 4.15,
S 19.01; found: C 49.73, H 3.39, N 4.20, S 18.95.
Methyl 1,2,4,5-Tetrahydro-1-methyl-2,5-dioxo-3-phenyl-2l4-pyrrolo[3,2-c]isothiazole-6-carboxylate (12).
To a stirred ice-cooled soln. of 0.31 g (1 mmol) of 10a in THF (50 ml) were added first 0.26 g (2 mmol) of I2
and then dropwise an ethanolic soln. of MeNH2 (8m, 2.0 ml, 16 mmol). The mixture was allowed to warm to r.t.,
acidified with 2n H2SO4, and extracted three times with CH2Cl2. The combined org. layers were washed
successively with sat. aq. H2SO3 soln. and with H2O, and finally dried (Na2SO4). The solvent was removed, and
the residue was purified by FC (hexane/AcOEt 1:1). Faintly yellow crystals from MeOH. 41% of 12. M.p. 240
2448 (dec.). M.p. and analytical data identical with [14]. 1H-NMR: 10.98 (s, 1 H); 7.66 7.42 (m, 5 H); 3.74
‡
(s, 3 H); 3.64 (s, 3 H). MS: 304 (M ), 121. Anal. calc. for C14H12N2O4S (304.32): C 55.25, H 3.97, N 9.21, S 10.54;
found: C 55.44, H 4.03, N 9.28, S 10.66.
Reaction of 5a with [Pt(h2-C2H4)(PPh3)2] (14) [28]. Compound 5a (29 mg, 0.1 mmol) was added to a soln.
of 14 (75 mg, 0.1 mmol) in toluene (10 ml). The color changed immediately from yellow to dark brown. After
stirring for 1 h at r.t., the soln. was concentrated in vacuo to 5 ml. Addition of hexane (20 ml) caused
precipitation of the crude material, which was collected by centrifugation and washed twice with Et2O (20 ml).
After drying in vacuo, the product was identified as PtII-complex 15 (64%). Orange-brown powder. M.p. 237
2398. IR: 3100w, 1714s, 1685s, 1655 (br.). 1H-NMR (CD2Cl2): 7.00 7.42 (m, 35 arom. H); 6.95 (s, NH); 3.37
(s, M e).13C-NMR (CD2Cl2): 165.78; 164.70; 150.84 (J ˆ 5.6); 141.12 (J ˆ 9.2); 135.40; 135.37; 135.31; 135.27;
131.11; 129.11; 128.54; 128.49; 128.23; 128.14; 128.03; 110.33; 50.31. 31P-NMR (CH2Cl2): 21.08, 21.49 (1J(Pt,P) ˆ
2939, 2927, 2J(P,P) ˆ 31.5). Anal. calc. for C49H39NO3P2PtS2 (1011.02): C 58.21, H 3.89, N 1.39, S 6.34; found:
C 58.65, H 3.86, N 1.21, S 6.35.
Reaction of 6-Ethyl 3-Methyl 4,5-Dihydro-4-methyl-5-oxo[1,2]dithiolo[4,3-b]pyrrole-3,6-dicarboxylate (13)
[1] with 14 [28]. A soln. of 13 (15 mg, 0.05 mmol) in 10 ml of MeCN was added dropwise to a soln. of 14 (38 mg,
0.05 mmol) in 10 ml of toluene. The color changed from yellow to orange-red. The soln. was stirred at r.t. for 2 h.
By a procedure similar to that described for 15, PtII-complex 16 was isolated and purified (67%). Orange-brown
1
powder. M.p. 237 2398. IR: 3070w, 2964m, 1711s, 1651s. H-NMR (CD2Cl2): 7.14 7.48 (m, 30 arom. H); 3.85
(q, J ˆ 7.1, CH2); 3.03 (s, MeN); 0.83 (t, J ˆ 7.1, MeCH2). 31P-NMR (CH2Cl2): 19.76, 22.07 (1J(Pt,P) ˆ 3010, 2951,
2J(P,P) ˆ 31.3). Anal. calc. for C47H41NO5P2PtS2 (1021.01): C 55.29, H 4.05, N 1.37, S 6.28; found: C 55.85,
H 3.96, N 1.29, S 6.35.
Reaction of 10a with 14 [28]. By a procedure similar to that for 15, with 21 mg (0.1 mmol) of 10a and 75 mg
(0.1 mmol) of 14 in 10 ml of toluene, PtII-complex 17 was prepared and purified to give a carmine product
(68%). M.p. 170 1728. IR: 3441w, 3051w, 1721s, 1709s (sh), 999m. 1H-NMR (CD2Cl2): 7.00 7.55 (m, 35 ar-
om. H); 6.73 (s, NH); 3.53 (s, M e).13C-NMR (CD2Cl2): 168.45; 163.90; 162.02; 140.85; 135.93 (J ˆ 5.6); 135.14;

Helvetica Chimica Acta Vol. 85 (2002)
4465
135.03; 134.91; 134.80; 131.61; 131.51; 131.49; 129.78; 129.13; 128.97; 128.90; 128.86; 128.79; 116.26 (J ˆ 4.2);
51.31. 31P-NMR (CH2Cl2): 19.72, 22.04. (1J(Pt,P) ˆ 2280, 3435, 2J(P,P) ˆ 30.5). Anal. calc. for C49H39NO4P2PtS2
(1027.02): C 57.31, H 3.83, N 1.36, S 6.33; found: C 56.95, H 4.08, N 1.42, S 6.48.
Reaction of 10b with 14 [28]. Compound 10b (22 mg, 0.07 mmol) was added to a soln. of 14 (50 mg,
0.07 mmol) in toluene (10 ml). The color changed immediately from yellow to light brown. The soln. was stirred
at r.t. for 10 h, while a yellow solid began to precipitate. The precipitate was collected by centrifugation, washed
twice with 20 ml of Et2O, and dried in vacuo. The product was identified as PtII-complex 18 (82%). Ochre-yellow
powder. M.p. 272 273: IR: 3443m, 3018m, 1717s, 1706s, 1628m, 1273s, 1094s. 1H-NMR (CD2Cl2): 7.10 7.75
(m, 35 arom. H); 6.05 (s, NH); 3.41 (s, M e). 13C-NMR (CD2Cl2): 166.44 (J ˆ 8.5); 166.24; 143.63 (J ˆ 6.9);
Table 4. Summary of Crystal Data for the Complexes 5a, 16, and 18
5a
16
18
Formula
Color
C13H9NO3S2
red
C47H41NO5P2PtS2
yellow
C49H39NO5P2PtS2 ¥ 2.12 H2O
yellow
Crystal size [mm]
Crystal system
Space group
0.04 Â 0.10 Â 0.22
monoclinic
I2/a (no. 15)
0.14 Â 0.42 Â 0.46
0.50 Â 0.50 Â 0.40
triclinic
monoclinic
≈
P1
P2/n
Unit-cell dimensions
a [ä]
b [ä]
c [ä]
a [8]
b [8]
g [8]
26.657(13)
3.9193(13)
27.424(13)
90
116.74(3)
90
12.605(1)
13.272(1)
14.741(1)
78.96(1)
75.53(1)
66.25(1)
2157.9(3)
2
13.224(3)
16.215(3)
22.671(4)
90
103.917(14)
90
Volume of unit cell [ä3]
Z
2559(2)
8
4718.6(15)
4
Formula weight
Density (calc.) (Mg/m3)
Absorption coefficient (mmÀ1
F(000)
Radiation
Temperature (K)
qmax [8]
291.3
1.512
0.400
1200
MoKa
295
1020.96
1.571
3.469
1020
MoKa
295
1081.2
1.518
3.204
2150.72
MoKa
295
)
25
25
25
Reflections collected
Independent reflections
Rint
5350
2264
0.0209
1486
7923
7550
0.0240
9008
8282
0.0213
7153
j F j> 3s
jFj
I > 2sI
6461
2
2
Quantity minimized
Extinction correction
Absorption correction
Transmission min./max.
Weighting scheme
Parameters refined
Residuals
S(j Fo jÀj Fc j )2
empirical
numerical
0.955/0.984
w ˆ sÀ2
S(j Fo j Àj Fc j )2
S(j Fo jÀj Fc j )2
no
no
numerical
0.328/0.568
w ˆ sÀ2
numerical
0.212/0.344
w ˆ sÀ2
179
525
690
Ra)
0.0601
0.0387
1.72
0.0365
0.0667
1.616
0.0421
0.0358
2.64
wRb)
sc)
Largest features of the final
difference Fourier synthesis [e ¥ äÀ3
‡ 0.42/ À 0.38
‡ 0.89/ À 0.87
‡ 0.91/ À 1.60
]
b
a) R ˆ S jj Fo j À j Fc j j /S j Fo j . ) wR ˆ [Sw(jFo j À j Fc j)2/Sw j Fo j ]1/2 and the j F j2 equiv., resp. c) s ˆ Sw(j Fo j À
2
j Fc j )2/(N À NP ) with N ˆ number of reflections, NP ˆ number of parameters; and the j F j 2 equiv.

4466
Helvetica Chimica Acta Vol. 85 (2002)
135.37; 135.25; 135.15; 134.69; 132.88 (J ˆ 4.9); 131.58; 131.53; 131.12; 131.00; 130.95; 129.88; 129.13; 129.56;
129.26; 128.97; 128.87; 125.84; 51.90. 31P-NMR (CH2Cl2): 7.47, 12.56 (1J(Pt,P) ˆ 2054, 3724, 2J(P,P) ˆ 20.7). Anal.
calc. for C49H39NO5P2PtS2 (1043.02): C 56.43, H 3.77, N 1.34, S 6.15; found: C 56.02, H 3.98, N 1.25, S 6.21.
X-Ray-Structure Analysis of 5a, 16, and 18. Intensity data have been collected on a Siemens P4 (16) and a
Siemens R3m/V (5a, 18) four-circle diffractometer, resp., with variable scan speed in w-scan mode with graphite
monochromated MoKa radiation. Background counts were taken with stationary crystal and stationary counter
at beginning and end of scan, each for 1/4 of the total scan time. A face-indexed numerical absorption correction
was applied. The phase problem was solved by means of the direct methods of the SHELXTL program suite.
2
Full-matrix least-squares refinement was based on j F j (16) and j F j (5a, 18), resp. The non-H-atoms have
been refined with anisotropic displacement parameters. H-atoms have been placed into calculated positions in
the final stages of refinement. Some disorder of H2O of crystallization was encountered in 18. Further
crystallographic data are compiled in Table 4.
Crystallographic data (excluding structure factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as deposition Nos. CCDC-198233 (16), 198234
(5a), and 198235 (18). Copies of the data can be obtained, free of charge, on application to the CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: ‡44(1223)336033; e-mail: deposit@ccdc.cam.uk).
We gratefully acknowledge financial support of the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie.
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Received June 20, 2002