Efficient new protocol to synthesize aromatic and heteroaromatic dithioesters

Article abstract of DOI:10.1055/s-2004-822311

A very efficient, high yielding procedure to synthesize substituted aromatic and heteroaromatic dithioesters is described. It involves the reaction between (phenylsulfonyl)methyl (hetero)aromatic derivatives and elemental sulfur in basic medium, followed by alkylation.

Full text of DOI:10.1055/s-2004-822311

928
PAPER
Efficient New Protocol to Synthesize Aromatic and Heteroaromatic
Dithioesters
New
Pro
s
tocol to S
a
ynthesize
A
b
romatic and
e
H
eteroarom
l
atic
D
l
ithioest
e
er
s
Abrunhosa, Mihaela Gulea, Serge Masson*
Laboratoire de Chimie Moléculaire et Thioorganique (LCMT), UMR CNRS 6507, ENSICAEN-Université de Caen, 6 Bd. Maréchal Juin,
14050 Caen, France
Fax +33(231)452877; E-mail: masson@ismra.fr
Received 15 December 2003; revised 14 January 2004
The present paper describes a facile and general proce-
Abstract: A very efficient, high yielding procedure to synthesize
dure, which, via phenylsulfonyl derivatives, allows the
preparation of hetero aromatic dithioesters in high yields.
As suggested by the authors,9 one of the reasons for the
matic derivatives and elemental sulfur in basic medium, followed
substituted aromatic and heteroaromatic dithioesters is described. It
involves the reaction between (phenylsulfonyl)methyl (hetero)aro-
by alkylation.
low yields obtained using the Mayer’s synthesis (despite
a complete conversion), is the competing alkylations of
the ammonium dithiocarboxylate by both CH3I and the
Key words: dithioester, sulfone, carbene insertion, arylsulfonyl
elimination
starting benzylic halide, affording the S-benzylic
dithioester in addition to the expected S-methyldithioester
(Scheme 1). Moreover, starting from a chloromethylpyri-
Dithioesters are widely used as synthetic tools1 which
have been involved in thiophilic addition of nucleophiles,
thioacylation of amines,2 in [4+2] or [3+2] cycloadditions
(as hetero dienophiles3 or dipolarophiles4), and also in
radical trapping5 or reversible addition fragmentation
transfer (RAFT) reactions.6 Furthermore, we recently re-
ported their application as starting substrates for a general
synthesis of various functionalized thiazolines7 and in
particular of chiral thiazoline-containing ligands.8
dinium hydrochloride, by-products resulting from an auto
N-alkylation products were also formed in basic medium.
These facts let us suppose that the replacement of the
halogen in the starting halide by another leaving group,
the latter leading to a non-alkylating substrate, could im-
prove the procedure. A phenylsulfonyl group seemed to
us a good candidate for this purpose.
In this preceding work,8 we had to prepare some
dithioesters bearing heteroaromatic moieties. For this pur-
pose, we used the reaction of the corresponding halome-
thylated aromatic derivative with elemental sulfur and
Et3N, followed by subsequent alkylation with CH3I (ac-
cording to the procedure described by Mayer9 and also de-
ArC(S)SMe
MeI
S8/Et3N, 1:8 (3 equiv)
+
ArCH2Hal
ArC(S)S HNEt3
20-60 °C, 7 h
DMF
ArC(S)SCH2Ar
Scheme 1
veloped by other authors).10 In these conditions, starting For a preliminary study of feasibility and optimization, we
from 2-picolyl chloride, 2-chloromethyl quinoline and 2- probed the synthesis of the methyl 2-pyridine dithiocar-
di(chloromethyl) pyridine, low to moderate yields have boxylate 3a from 2-picolyl phenyl sulfone 2a, as model
been obtained for the corresponding dithioesters: methyl substrate (Scheme 2). We first prepared the starting sul-
pyridine-2-dithiocarboxylate (50–60%), methyl quino- fone from commercial 2-picolyl chloride hydrochloride
line-2-dithiocarboxylate (40–45%) and dimethyl pyri- 1a and sodium phenylsulfinate, using catalytic amount of
dine-2,6-dithiocarboxylate (25–40%). These yields were tetrapropyl ammonium bromide (Pr4N+Br–) as phase
unsatisfactory for our synthetic purpose since the starting
transfer agent. In this example, the reaction was carried
commercial halogeno derivatives are sometimes relative- out in the presence of one equivalent of base DBU, in or-
ly expensive. Other methods to prepare aromatic or het- der to liberate in situ picolyl chloride from its pyridinium
eroaromatic dithioesters (from carbanions and carbon salt. The sulfone 2a was isolated in quasi-quantitative
disulfide,11 using Lawesson’s12 or Davy’s13 reagents, yield (98%) and could be used without further purification
from arylimidates with H2S14 by Friedel–Crafts dithiocar- for the next step. Then, the sulfuration step was carried out
boxylation,15 dithiolanes fragmentation,16 etc) could not by reacting 2-picolyl phenyl sufone 2a with octasulfur
be easily adapted to our substrates,17 therefore, we have (S8) in different conditions and, after subsequent alkyla-
focused our study toward the search of a more efficient tion with CH3I, the desired dithioester 3a was obtained.
synthesis.
As shown in Table 1, the base/solvent selection played an
important role in the reaction, connected to the acidity of
the proton in alpha position of the phenylsulfonyl group.
The best yield and shorter reaction time were obtained us-
ing t-BuOK/THF (Table 1, entry 3).
SYNTHESIS 2004, No. 6, pp 0928–0934
Advanced online publication: 15.03.2004
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DOI: 10.1055/s-2004-822311; Art ID: P10303SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
New Protocol to Synthesize Aromatic and Heteroaromatic Dithioesters
929
Table 2 Synthesis of Dithioesters 3b–n from Sulfones 2b–n
Table 1 Optimization of Synthesis of Dithioester 3a from 2-Picolyl
Phenyl Sulfone 2a
Entry
1
Sulfone
2b
2c
Time (h)
Product 3
3b
Yield%
80
Entry
Base
Solvent
DMF
Time (h)
Yield% 3a
3
3
1
2
3
NEt3
12
12
3
15
82
94
2
3c
86
DBU
t-BuOK
CH3CN
THF
3
2d
2e
12
6
3d
98
4
3e
92
5
2f
24
6
3f
58
1) S8/base, 1:8 (3 equiv)
r.t., time, solvent
2) MeI, 1h
PhSO2Na
6
2g
3g
70
cat. Pr4NBr
7
2h
2i
6
3h
87
SMe
CH3CN, DBU
80 °C, 24h
N
N
N
HCl
8
6
3i
92
3a
2a
S
Cl
S O
98 %
1a
Ph
+
O
9
2j
6
3j
98
PhSO2Me
10
11
12
13
2k
2l
6
3k
68
Scheme 2
6
3l
75
This optimized result incited us to extend our new proto-
col to the preparation of various aromatic and heteroaro-
matic dithioesters, starting from the corresponding
sulfone precursors (Scheme 3, Table 2). Therefore, using
the above-described method, a series of phenylsulfonylm-
ethyl substituted aromatics 2b, 2c, 2e–l and the bis-deriv-
atives 2d, 2m, 2n (Figure 1) were first prepared in quasi-
quantitative yields from commercial (or easily
available18) benzylic type halides 1b–n and sodium phe-
nylsulfinate, in the presence of tetrapropyl ammonium
bromide (the use of one equivalent of DBU was again nec-
essary when the starting halide was a pyridinium or quin-
olinium hydrochloride). The reaction of crude sulfones
with octasulfur using t-BuOK in THF and subsequent
alkylation, afforded the dithioesters 3b, 3c, 3e–l and the
bis-dithioesters 3d, 3m, most often in very good yields
(Table 2, entries 1–12, Figure 2). In particular, the pyri-
dine and quinoline dithioesters 3a, 3d and 3e, precursors
of thiazoline ligands,8 could be synthesized easily at a rel-
atively large scale (5–10 g), demonstrating the high effi-
ciency of the method.
2m
2n
12
24
3m
3n
52
0
2-, 3- and 4-substituted pyridine dithiocarboxylates 5a–c,
respectively. The preparation of these compounds is not
possible by direct oxidation of the nitrogen of the pyridine
dithiocarboxylates 3a–c; the oxidation occurs on the sul-
fur of the thiocarbonyl function to give a sulfine.10,17
Therefore, by oxidation of sulfones 2a–c with MCPBA,
we first prepared the (phenylsulfonyl)methylpyridines N-
oxides 4a–c (yield, 92–95%). Subsequent reaction of 4a–
c with S8/t-BuOK and methylation, led to the desired
products 5a–c in 70–75% yield (Scheme 4).
SO2Ph
SO2Ph
N
N
N
SO2Ph
SO2Ph
2d
2c
2b
S
ii, iii
i
+
Ar(CH2SO2Ph)1,2
Ar(C-SMe)1,2
Ar(CH2Hal)1,2
PhSO2Me
SO2Ph
N
> 90 %
N
1b-n
2b-n
3b-n
2f
2e
PhO2S
Scheme 3 Reagents and Conditions:i PhSO2Na, CH3CN, cat.
Pr4NBr, 80 °C, 24 h; ii S8/t-BuOK, r.t., time, THF; iii MeI, 1 h
SO2Ph
SO2Ph
Only the expected bis(dithioester) 3n was not obtained
starting from the bis(sulfone) 2n, probably because of the
proximity of the two ortho-functions which can induce
unfavorable steric hindrance or undesirable intramolecu-
lar reactions.
X
SO2Ph
SO2Ph
2m
SO2Ph
2n
2g-l
g : X = H; h: X = F;
i: X = Br; j: X = I;
k: X= MeO; l: X = NO2
Figure 1 Aromatic and heteroaromatic methyl(phenylsulfones)
This method, involving sulfones, also allowed the synthe-
sis of an unknown type of dithioesters, the N-oxides of
Synthesis 2004, No. 6, 928–934 © Thieme Stuttgart · New York

930
I. Abrunhosa et al.
PAPER
S
SMe
ally demonstrated by an early treatment with CH3I of the
reaction mixture (after 2 h, when DBU/CH3CN conditions
was used) leading to the isolation of a small amount of
methyl sulfide II (Ar = 2-pyridyl). Deprotonation of i-2
into i-4 followed by sulfuration leading to i-5, which af-
fords, by regression of the polysulfur chain and b-elimina-
tion of the phenyl sulfinate anion, the dithiocarboxylate i-
7, the precursor of the dithioester III. As an alternative fi-
nal pathway, the anionic intermediate i-4 could, by ther-
mal decomposition at room temperature, loose the phenyl
sulfinate anion to afford the carbene species i-6. The latter
can react intramolecularly with the sulfide anion giving
the cyclic polysulfide carbanion i-9, which is then con-
verted into the above-mentioned i-7 by cycloreversion. A
related carbene formation from magnesium dithioacetal
carbanions, followed by nucleophilic addition, has been
reported.19 Beside this first route, the direct decomposi-
tion of the initial carbanion i-1 into the carbene i-3 (route
B) cannot be excluded. Indeed, the generation of a car-
bene, by heating an aryl methyl(phenylsulfone) in the
presence of a base has been also recently reported.20 Then,
carbene i-3 could, via insertion in the S–S bond of S8 and
deprotonation, lead also to the cyclic polysulfide i-9 from
which, as we already suggested, the dithiocarboxylate i-7
could be obtained.
S
SMe
MeS
SMe
N
3c
N
3d
N
3b
S
S
SMe
N
N
3f
3e
S
S
SMe
S
S
SMe
SMe
SMe
MeS
SMe
X
3g-l
S
S
S
3m
3n
Figure 2 Aromatic and heteroaromatic methyldithiocarboxylates
S
ii
i
70-75 %
92-95 %
SO2Ph
SMe
SO2Ph
N
N
N
2a-c
O
4a-c
O
5a-c
Scheme 4 Reagents and conditions: i MCPBA/CH2Cl2, 0 °C–r.t.,
12 h; ii 1)S8/t-BuOK, r.t., 12 h. THF, 2) MeI, 1 h
Ar
H
SO2Ph
H
Our attempts to generalize this procedure to the prepara-
tion of aliphatic dithioesters (benzyl and tert-butyl dithio-
carboxylates), failed in the different base/solvent tested
conditions (DBU/CH3CN, t-BuOK/THF, n-BuLi/THF).
This limitation could be due to the lower acidity of the
proton a to the sulfonyl group in the starting sulfones. In-
deed, in an additional experiment, starting from the sulfo-
nylated phosphonate 6, sulfone in which the aromatic
moiety is replaced by another electron-withdrawing sub-
stituent, the phosphoryl group, the phosphono-dithiofor-
mate 7 was obtained in 67% yield (Scheme 5).
I
base
Ar
Ar
H
SO2Ph
route A
S8
route B
PhSO2
SO2Ph
Ar
CH
i-3
S8
S
i-1
H
(S)6
S
i-2
base
Ar
SO2Ph
Ar
S
S
S
S
S
Ar
SO2Ph
(S)6
S
(S)4
O
P
H
S
O
P
1) S8/DBU
CH3CN, r.t., 24h
i-4
i-2'
MeI
SO2Ph
i-8
SMe
SO2Ph
EtO
EtO
EtO
EtO
S8
-PhSO2
2) MeI, 1h
67 %
base
Ar
6
S
7
Ar
Ar
C
Ar
S
SO2Ph
S
S
Scheme 5
SMe
S
S
S
S
II
(S)6
S
(S)
6 (S)6
(S)4
S
To our knowledge, no mechanism has been suggested so
far in the publications related to the sulfuration of benzyl-
ic halides in basic medium. We propose here a mechanism
for the synthesis of dithioesters by sulfuration of benzyl-
sulfones (Scheme 6). The first step should proceed
through the carbanion i-1, generated by deprotonation of
the sulfone I. Then, a possible mechanism (route A)
would involve the electrophilic attack of S8 on the carban-
ion i-1 leading to the intermediate i-2. The latter can give
the thiolate i-2¢, by regression of the polysulfide chain.
The presence of this thiolate (which can lead back to a
polysulfide of type i-2 by reaction with sulfur) was actu-
S
i-6
i-5
i-9
Ar
-PhSO2
S
S
S
i-7
MeI
Ar
MeS
III
Scheme 6
Synthesis 2004, No. 6, 928–934 © Thieme Stuttgart · New York

PAPER
New Protocol to Synthesize Aromatic and Heteroaromatic Dithioesters
931
2,6-Bis(benzenesulfonylmethyl)pyridine (2d)
Yield: 96%; white solid; mp 175 °C.
In conclusion, we have proposed a very efficient synthetic
procedure for the preparation of various aromatic and het-
eroaromatic dithioesters, simply by reacting the easily IR (KBr): 3068, 1588, 1452, 1404, 1308, 1252, 1224, 1152, 1080
cm–1.
available (phenylsulfonyl)methyl aromatic derivatives
1H NMR (CDCl3, 400 MHz): d = 4.37 (s, 4 H, 2 × CH2SO2), 7.25
(d, 3J = 7.8 Hz, H-3, H-5, 2 H), 7.46–7.50, 7.60–7.68 (m, 10 H, 2 ×
C6H5), 7.78 (t, 3J = 7.8 Hz, H-4, 1 H).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 64.6 (2 × CH2), 125.6,
128.8, 129.4, 134.2, 137.8, 138.8, 149.6.
with elemental sulfur in basic medium and subsequent
alkylation. Further studies, related to the reactivity of
some of these new (hetero)aromatic dithioesters, are in
progress and will be published in due course.
MS (EI): m/z (%) = 387 (9) [M+], 323 (56), 258 (100), 182 (37), 167
(15), 141 (6), 104 (12), 77 (35), 51 (20).
Most of the reactions were monitored by TLC using silica plates.
Synthesized products were purified by flash column chromatogra-
phy on silica gel and crystallized if necessary. Solvents were dried
Anal. Calcd for C19H17NS2O4 (387.059): C, 58.90; H, 4.42; S,
16.52; N, 3.61. Found: C, 58.48; H, 4.37; S, 16.33; N, 3.90.
1
by distillation prior use. H NMR spectra were recorded with a
Brüker DPX 250 MHz or a Brüker DRX 400 MHz spectrometer.13C
NMR {H} spectra were recorded with a Brüker DPX 250 MHz
spectrometer. TMS was used as internal standard. Chemical shifts
(d) are given in ppm and coupling constants (J) in Hz, conventional
abbreviations are used. Melting points are uncorrected. The infrared
spectra were recorded with a Perkin-Elmer 16 PC spectrometer on
the liquid film. Mass spectra were recorded with a Nermag R 10
10H spectrometer in electronic impact at 70 eV, m/z and relative
abundance are given. HRMS were obtained with a JEOL JMS-AX
500 mass spectrometer. Elemental microanalyses were performed
on an automatic apparatus CHNS-O ThermoQuest.
2-Benzenesulfonylmethylquinoline (2e)24
Yield: 97%; RN: [65492-27-5].
1H NMR (CDCl3, 250 MHz): d = 4.76 (s, 2 H), 7.38–7.44, 7.51–
7.69, 7.81–7.84, 8.15–8.19 (4 × m, 11 H).
8-Benzenesulfonylmethylquinoline (2f)
Yield: 76%, brown solid, mp 188 °C.
IR (KBr): 3060, 2970, 2930, 1580, 1500, 1160, 1130, 1080 cm–1.
1H NMR (CDCl3, 400 MHz): d = 5.25 (s, 2 H, CH2SO2Ph), 7.26–
7.28 (m, 3 H, H-3, 2 × Harom), 7.40 (dd, 3J = 8.2 Hz, 3J = 7.4 Hz, 1
H, H-6), 7.53 (m, 3 H, 3 × Harom), 7.82 (dd, 3J = 8.2 Hz, 4J = 1.1 Hz,
Compounds 2a–c, 2g, 2i–l, 4a–c, 3a,b, 3e, 3g,h, 3k, 3m, 6 and 7
have been already described and their spectral and physical data
were found in complete agreement with that given in the literature.
For these compounds, the registry number (RN) and a reference are
given, together with the yield obtained using our procedures and the
observed 1H NMR data for comparison.
3
1 H, H-5), 7.90 (dd, J = 7.4 Hz, 4J = 1.1 Hz, 1 H, H-7), 8.06 (dd,
4J = 1.5 Hz, 3J = 8.2 Hz, 1 H, H-4), 8.57 (dd, 3J = 4.1 Hz, 4J = 1.5
Hz, 1 H, H-2).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 58.0 (CH2SO2Ph), 122.4,
127.5, 128.3, 129.3, 129.7, 130.0, 130.3, 133.9, 134.5, 137.3, 139.8,
147.6, 151.0.
MS (EI): m/z (%) = 283 (7) [M+], 219 (16), 142 (100), 115 (22), 89
(8), 77 (11), 63 (5), 51 (12).
Benzenesulfonylmethyl Aromatics (2); General Procedure
A mixture of benzyl halide 1 (1a–c, 1e–l) (10 mmol), sodium phe-
nylsulfinate (15 mmol), and catalytic amount of tetrapropyl ammo-
nium bromide (2 mmol), in CH3CN (10 mL), was refluxed for 12 h.
Additional DBU (10 mmol) is necessary when the starting halide is
a ammonium hydrochloride (1a–c, 1e). Then the solvent was re-
moved under vacuum and the residue was dissolved in CH2Cl2 (20
mL), washed with brine (20 mL), dried (MgSO4) and the solvent re-
moved. The crude product was obtained in quasi-quantitative yield,
as a white solid and was used without purification in the next step.
Starting from the bis-halides 1d, 1m or 1n (10 mmol), 30 mmol of
sodium phenylsulfinate and 4 mmol of tetrapropyl ammonium bro-
mide were necessary.
Benzenesulfonylmethylbenzene (2g)25
Yield: 98%; RN: [3112-88-7].
1H NMR (CDCl3, 250 MHz): d = 4.33 (s, 2 H), 7.11 (m, 1 H), 7.26–
7.34, 7.45–7.49, 7.60–7.66 (3 × m, 9 H).
2-Benzenesulfonylmethylfluorobenzene (2h)
Yield: 93%; white solid; mp 139 °C.
IR (KBr): 3070, 3030, 2980, 2920, 1620, 1580, 1490, 1450, 1410,
1290, 1260, 1230, 1160, 1130, 1080 cm–1.
2-Benzenesulfonylmethylpyridine (2a)21
Yield: 98%.
1H NMR (CDCl3, 400 MHz): d = 4.40 (s, 2 H, CH2SO2), 6.97 (t,
3J = 9.3 Hz, 1 H, Harom), 7.11 (t, 3J = 7.5 Hz, 1 H, Harom), 7.29–7.35,
7.42–7.48, 7.58–7.68 (m, 7 H, 7 × Harom).
1H NMR (CDCl3, 250 MHz): d = 4.58 (s, 2 H), 7.25 (ddd, 3J = 7.5
3
4
Hz, J = 5.0 Hz, J = 1.2 Hz, 1 H), 7.46–7.51 (m, 3 H), 7.62 (dt,
19F NMR: –117.60 (ddd, 3JFH6 = 12.72 Hz, 4JFH5 = 4JFH3 = 7.2 Hz).
3J = 3J = 7.5 Hz, J = 3.5 Hz, 1 H), 7.68–7.74 (m, 3 H), 8.41 (dd,
4
3J = 7.5 Hz, 4J = 1.2 Hz, 1 H).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 55.7 (d, 3JCF = 2.5 Hz, CH2),
115.6 (d, 2JCF = 21.7 Hz, C-3), 115.9 (d, 2JCF = 14.5 Hz, C-2), 124.5
(d, 3JCF = 3.7 Hz, C-6), 128.7, 129.1, 131.1 (d, 3JCF = 8.3 Hz, C-4),
132.8 (d, 4JCF = 2.7 Hz, C-5), 134.0, 138.0, 161.3 (d, JCF = 249.9 Hz,
CF).
3-Benzenesulfonylmethylpyridine (2b)22
Yield: 90%.
1H NMR (CDCl3, 250 MHz): d = 4.31 (s, 2 H), 7.26–7.67 (3 × m, 7
H), 8.17 (d, 4J = 2.1 Hz, 1 H), 8.57 (dd, 3J = 4.2 Hz, 4J = 1.4 Hz, 1
Anal. Calcd for C19H17NS2O4 (387.059): C, 62.38; H, 4.43; S,
12.81. Found: C, 62.38; H, 4.56; S, 13.13.
H).
4-Benzenesulfonylmethylpyridine (2c)23
Yield: 98%.
2-Benzenesulfonylmethylbromobenzene (2i)26
Yield: 96%.
1H NMR (CDCl3, 250 MHz): d = 4.61 (s, 2 H), 7.21 (dt, 3J = 3J = 7.6
Hz, 4J = 1.6 Hz, 1 H), 7.38 (dt, 3J = 3J = 7.6 Hz, 4J = 1.1 Hz, 1 H),
7.45–7.52, 7.62–7.67 (2 × m, 7 H).
1H NMR (CDCl3, 250 MHz): d = 4.31 (s, 2 H), 7.09 (d, 3J = 5.9 Hz,
2 H), 7.52–7.73 (2 × m, 5 H), 8.19 (d, 3J = 5.9 Hz, 2 H).
Synthesis 2004, No. 6, 928–934 © Thieme Stuttgart · New York

932
I. Abrunhosa et al.
PAPER
2-Benzenesulfonylmethyliodobenzene (2j)27
3-Benzenesulfonylmethylpyridine N-Oxide (4b)30
Yield: 95%.
Yield: 94%.
1H NMR (CDCl3, 250 MHz): d = 4.61 (s, 2 H), 7.21 (dt, 3J = 3J =
7.6 Hz, 4J = 1.5 Hz, 1 H), 7.38 (t, 1 H, 3J = 3J = 7.6 Hz, 1 H), 7.46–
7.50 (m, 2 H), 7.53 (d, 3J = 7.6 Hz, 1 H), 7.63–7.68 (m, 3 H), 7.76
(d, 3J = 7.6 Hz, 1 H).
1H NMR (CDCl3, 400 MHz): d = 4.24 (s, 2 H), 7.17–7.28, 7.52–
7.75, 7.87–7.89, 8.17–8.20 (4 × m, 9 H).
4-Benzenesulfonylmethylpyridine N-Oxide (4c)30
Yield: 93%.
2-Benzenesulfonylmethylmethoxybenzene (2k)28
Yield: 97%.
1H NMR (CDCl3, 250 MHz): d = 3.33 (s, 3 H), 4,45 (s, 2 H), 6.64
(d, 3J = 8.2 Hz, 1 H), 6.93 (t, 3J = 3J = 7.5 Hz, 1 H), 7.23–7.32, 7.36–
7.43, 7.52–7.62 (3 × m, 7 H).
1H NMR (CDCl3, 400 MHz): d = 4.27 (s, 2 H), 7.08 (d, 3J = 5.9 Hz,
3
2 H), 7.52–7.57, 7.68–7.7.73 (2 × m, 5 H), 8.19 (d, J = 5.9 Hz, 2
H).
Aromatic Carbodithioic Acid Methyl Esters 3 and 5; General
Procedure
2-Benzenesulfonylmethylnitrobenzene (2l)28
Yield: 96%.
A mixture of sulfone 2 or 4 (10 mmol) and elemental sulfur (30
mmol) was placed into THF (10 mL) under magnetic stirring. After
addition of t-BuOK (30 mmol), the color of the solution changed to
dark brown. The reaction was stirred at r.t. for 3–12 h, depending on
the substrate. Then, CH3I (30 mmol) was added drop wise to the so-
lution and the stirring was continued for 1 h. The color usually
changed to orange-red.
1H NMR (CDCl3, 250 MHz): d = 4.96 (s, 2 H), 7.48–7.71 (m, 8 H),
7.98 (dd, 3J = 8.1 Hz, 4J = 1.1 Hz, 1 H).
1,3-Bis(benzenesulfonylmethyl)benzene (2m)
Yield: 93%; white solid; mp 172 °C.
The same procedure could be used by replacing THF with CH3CN
and t-BuOK by DBU (in this case reaction time is longer, i.e., 12–
48 h).
IR (KBr): 3366, 3030, 2972, 1448, 1292, 1256, 1166, 1154, 1128
cm–1.
1H NMR (CDCl3, 400 MHz): d = 4.24 (s, 4 H, 2 × CH2SO2), 7.01
(dd, 3J = 8.4 Hz, 4J = 1.4 Hz, H-4, H-6, 2 H), 7.06 (d, 4J = 1.4 Hz,
H-2, 1 H), 7.17 (t, 3J = 8.4, H-5, 1 H), 7.44–7.50, 7.59–7.66 (2 × m,
10 H, 2 × C6H5).
In both cases, the solvent was removed under vacuum and the resi-
due, dissolved in CH2Cl2 (2-5 mL), directly purified by chromatog-
raphy on silica gel, afforded pure dithioesters 3 or 5.
Starting from the bis-sulfones 2d or 2m (10 mmol), 60 mmol of sul-
fur and 60 mmol of t-BuOK and 60 mmol of CH3I were necessary.
13C {1H} NMR (CDCl3, 62.9 MHz): d = 62.8 (2 × CH2), 128.9,
129.0, 129.2, 129.4, 131.6, 133.6, 134.2, 138.3.
MS (EI): m/z (%) = 386 (5) [M+], 245 (100), 181 (48), 166 (10), 141
(4), 125 (1), 104 (19), 77 (21), 51 (11).
Pyridine-2-carbodithioic Acid Methyl Ester (3a)10
Yield: 94%.
1H NMR (CDCl3, 250 MHz): d = 2.75 (s, 3 H), 7.34 (ddd, 3J = 4.9
Hz, 3J = 7.6 Hz, 4J = 0.9 Hz, 1 H), 7.78 (ddd, 3J = 8.5 Hz, 3J = 7.6
Hz, 4J = 1.8 Hz, 1 H), 8.32 (dd, 3J = 8.5 Hz, 4J = 0.9 Hz, 1 H), 8.62
(dd, 3J = 4.9 Hz, 4J = 1.8 Hz, 1 H).
Anal. Calcd for C19H17NS2O4 (386.0646): C, 62.15; H, 4.69; S,
16.59. Found: C, 61.74; H, 4.69; S, 16.60.
1,2-Bis(benzenesulfonylmethyl)benzene (2n)
Yield: 95%; white solid, mp 143 °C.
Pyridine-3-carbodithioic Acid Methyl Ester (3b)10
Yield: 94%.
IR (KBr): 3356, 3060, 2994, 1448, 1318, 1296, 1172, 1146, 1130
cm–1.
1H NMR (CDCl3, 250 MHz): d = 2.81 (s, 3 H), 7.47 (ddd, 3J = 4.9
Hz, 3J = 7.9 Hz, 4J = 0.6 Hz, 1 H), 8.23 (dt, 3J = 7.6 Hz, 4J = 4J = 1.5
Hz, 1 H), 8.74 (dd, 3J = 4.9 Hz, 4J = 1.5 Hz, 1 H), 8.62 (d, 4J = 1.5
Hz, 1 H).
1H NMR (CDCl3, 400 MHz): d = 4.54 (s, 4 H, 2 × CH2SO2), 6.94,
7.19 (2 × dd, J = 5.7 Hz, J = 3.4 Hz, 4 H, H-3, H-4, H-5, H-6), 7.47–
7.53, 7.62–7.70 (2 × m, 10 H, 2 × C6H5).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 60.3 (2 × CH2), 128.8,
129.1, 129.5, 129.6, 133.6, 134.4, 138.5.
Pyridine-4-carbodithioic Acid Methyl Ester (3c)
Yield: 86%; dark red solid; mp 68 °C.
MS (EI): m/z (%) = 386 (5) [M+], 245 (100), 181 (76), 166 (11), 141
(4), 125 (16), 104 (14), 77 (26), 51 (14).
1H NMR (CDCl3, 400 MHz): d = 2.81 (s, 3 H, SCH3), 7.74 (dd, 3J =
4.5 Hz, 4J = 1.6 Hz, H-3, H-5, 2 H), 8.70 (dd, 3J = 4.5 Hz, 4J = 1.8
Hz, H-2, H-6, 2 H). 17b
Anal. Calcd for C19H17NS2O4 (386.0646): C, 62.15; H, 4.69; S,
16.59. Found: C, 61.80; H, 4.55; S, 16.56
13C {1H} NMR (CDCl3, 62.9 MHz): d = 21.0 (SCH3), 120.4, 150.7,
150.6, 178.2, 226.9 (C=S).
Benzenesulfonylmethylpyridine N-Oxides (4); General Proce-
dure
A solution of picolyl sulfone 3a, 3b, or 3c (2 mmol) in CH2Cl2 (5
mL), was cooled in an ice-bath at 0 °C. The MCPBA (2 mmol) in
CH2Cl2 (5 mL) was added slowly under magnetic stirring and then
the ice-bath was removed. After 12 h, the cloudy reaction mixture
was washed with a 2 M NaOH solution (5 mL), then extracted with
EtOAc (2 × 15 mL), dried (MgSO4) and the solvent removed. The
crude product 4a, 4b, or 4c, obtained as a white solid, was used
without further purification in the next step.
Pyridine-2,6-dicarbodithioic Acid Dimethyl Ester (3d)
Yield: 98%; spectral data were given in our previous work.8
Quinoline-2-carbodithioic Acid Methyl Ester (3e)9
Yield: 92%; RN: [67333-55-5].
1H NMR (CDCl3, 250 MHz): d = 2.80 (s, 3 H), 7.63 (dd, 3J = 7.0 Hz,
3J = 8.1 Hz, 1 H), 7.79 (ddd, 3J = 8.3 Hz, 3J = 7.0 Hz, 4J = 1.4 Hz,
1 H), 7.86 (dd, 3J = 8.1 Hz, 4J = 1.4 Hz, 1 H), 8.21 (d, 3J = 8.5 Hz,
1 H), 8.24 (d, 3J = 8.3 Hz, 1 H), 8.83 (d, 3J = 8.5 Hz, 1 H).
2-Benzenesulfonylmethylpyridine N-Oxide (4a)29
Yield: 92%.
Quinoline-8-carbodithioic Acid Methyl Ester (3f)
Yield: 58%, red oil.
1H NMR (CDCl3, 400 MHz): d = 4.93 (s, 2 H), 7.20–7.29, 7.47–
7.51, 7.61–7.65, 7.80–7.82 (4 × m, 8 H), 8.41 (d, 3J = 6.3 Hz, 1 H).
Synthesis 2004, No. 6, 928–934 © Thieme Stuttgart · New York

PAPER
New Protocol to Synthesize Aromatic and Heteroaromatic Dithioesters
933
IR (NaCl): 3060, 3000, 2920, 1490, 1330, 1310, 1140, 1120, 1080
cm–1.
MS (EI): m/z (%) = 213 (3) [M+], 197 (6), 181 (5), 165 (100), 150
(59), 136 (13), 122 (16), 108 (18), 93 (6), 76 (10), 45 (14).
1H NMR (CDCl3, 400 MHz): d = 2.77 (s, 3 H, SCH3), 7.30 (d, 3J =
4.2 Hz, 1 H, H-3), 7.42 (dd, 3J = 7.2 Hz, 3J = 8.1 Hz, 1 H, H-6), 7.63
(dd, 3J = 7.2 Hz, 4J = 1.4 Hz, 1 H, H-7), 7.73 (dd, 3J = 8.1 Hz, 4J =
1.4 Hz, 1 H, H-5), 8.04 (dd, 3J = 8.3 Hz, 4J = 1.8 Hz, 1 H, H-4), 8.85
(dd, 3J = 4.2 Hz, 4J = 1.8 Hz, 1 H, H-2).
Anal. Calcd for C8H7NO2S2 (212.99): C, 45.05; H, 3.31; N, 6.57.
Found: C, 45.15; H, 3.52; S, 6.44.
Benzene-1,3-dicarbodithiobenzoic Acid Dimethyl Ester (3m)33
Yield: 52%.
13C {1H} NMR (CDCl3, 62.9 MHz): d = 21.6 (SCH3), 121.5, 126.1,
1H NMR (CDCl3, 250 MHz): d = 2.79 (s, 6 H), 7.42 (t, 3J = 3J = 7.9
Hz, 1 H), 8.13 (dd, 3J = 7.9 Hz, 4J = 1.9 Hz, 2 H), 8.59 (t, 4J = 4J =
1.9 Hz, 1 H).
128.2, 130.0, 134.0, 136.5, 146.5, 151.2, 231.4 (C=S).
Dithiobenzoic Acid Methyl Ester (3g)31
Yield: 70%.
N-Oxy-pyridine-2-carbodithioic Acid Methyl Ester (5a)
Yield: 71%; dark red solid; mp 99 °C.
IR (KBr): 3060, 3010, 1430, 1270, 1160, 1050 cm–1.
1H NMR (CDCl3, 250 MHz): d = 2.81 (s, 3 H), 7.28–7.40 (m, 3 H),
7.75–7.90 (m, 2 H).
1H NMR (CDCl3, 400 MHz): d = 2.78 (s, 3 H, SCH3), 7.28–7.37 (m,
2 H, H-5, H-4), 8.04 (dd, 4J = 2.5 Hz, 3J = 7.9 Hz, 1 H, H-3), 8.62
(dd, 3J = 6.5 Hz, 4J = 1.6 Hz, 1 H, H-6).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 22.1 (SCH3), 125.6, 126.7,
14.6, 178.2, 218.5 (C=S).
2-Fluoro-dithiobenzoic Acid Methyl Ester (3h)32
Yield: 87%.
1H NMR (CDCl3, 250 MHz): d = 2.81 (s, 3 H), 7.11–7.20 (m, 2 H),
7.43 (m, 1 H), 7.62 (dt, 3J = 3J = 7.6 Hz, 4J = 1.8 Hz, 1 H).
MS (EI): m/z (%) = 185 (20) [M+], 169 (21), 155 (33), 137 (54), 122
(95), 106 (10), 93 (18), 78 (100), 69 (14), 51 (34).
2-Bromo-dithiobenzoic Acid Methyl Ester (3i)
Yield: 92%; red oil.
Anal. Calcd for C7H7NOS2 (184,99): C, 45.38; H, 3.81; N, 7.56.
Found: C, 45.41; H, 3.81; N, 7.56.
IR (NaCl): 3040, 2900, 1580, 1450, 1420, 1270, 1250, 1230, 1080,
1030 cm–1.
1H NMR (CDCl3, 400 MHz): d = 2.81 (s, 3 H, CH3S), 7.22–7.28,
7.30–7.35 (m, 3 H, 3 × Harom), 7.62 (d, J = 8.0 Hz, 1 H, Harom).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 21.1 (CH3), 118.8 (C-Br),
127.6, 128.4, 130.6, 133.8, 147.9 (CC=S), 230.5 (C=S).
MS (EI): m/z (%) = 248 (57) [M+], 246 (55), 201 (100), 199 (98),
167 (8), 157 (5), 134 (2), 120 (43), 108 (5), 93 (12), 76 (12), 45 (20).
N-Oxy-pyridine-3-carbodithioic Acid Methyl Ester (5b)
Yield: 65%; dark red solid; mp 119–120 °C.
IR (KBr): 3050, 3010, 1430, 1270, 1170, 1050 cm–1.
1H NMR (CDCl3, 400 MHz): d = 2.82 (s, 3 H, SCH3), 7.33 (dd, 3J =
6.5 Hz, 3J = 8.1 Hz, 1 H, H-5), 7.81 (d, 3J = 8.1 Hz, 1 H, H-4), 8.34
(d, 3J = 6.5 Hz, 1 H, H-6), 8.78 (s, 1 H, H-2).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 21.2 (SCH3), 123.9, 125.8,
2-Iodo-dithiobenzoic Acid Methyl Ester (3j)
Yield: 99%; orange-red oil.
137.5, 141.3, 143.4, 221.4 (C=S).
MS (EI): m/z (%) = 185 (69) [M+], 169 (58), 138 (25), 122 (100),
106 (7), 95 (11), 78 (19), 69 (32), 51 (11).
IR (NaCl): 3040, 2900, 1690, 1570, 1450, 1420, 1270, 1250, 1230,
1070, 1080, 1010 cm–1.
1H NMR (CDCl3, 400 MHz): d = 2.78 (s, 3 H, CH3S), 7.07 (dt, 3J =
7.7 Hz, 4J = 1.8 Hz, 1 H, H-4), 7.28–7.40 (m, 2 H, H-5, H-6), 7.89
(dd, 3J = 7.7 Hz, 4J = 0.8 Hz, 1 H, H-3).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 21.1 (CH3S), 93.8 (CI),
127.2, 128.4, 130.5, 140.3, 151.6 (CC=S), 233.2 (C=S).
MS (EI): m/z (%) = 294 (75) [M+], 247 (100), 203 (1), 167 (39), 152
(5), 120 (29), 108 (6), 93 (6), 69 (6), 45 (9).
Anal. Calcd for C7H7NOS2 (184,99): C, 45.38; H, 3.81; N, 7.56.
Found: C, 45.51; H, 3.83; N, 7.52.
N-Oxy-pyridine-4-carbodithioic Acid Methyl Ester (5c)
Yield: 75%; dark red solid; mp 110 °C.
IR (KBr): 3090, 3020, 1470, 1270, 1160, 1040 cm–1.
1H NMR (CDCl3, 400 MHz): d = 2.82 (s, 3 H, SCH3), 7.98 (d, 3J =
6.7 Hz, 2 H, H-3, H-5), 8.17 (d, 3J = 6.7 Hz, 2 H, H-2, H-6).
Anal. Calcd for C8H7IS2 (293.90): C, 32.66; H, 2.40; S, 21.80.
Found: C, 32.82; H, 2.39; S, 21.39.
13C {1H} NMR (CDCl3, 62.9 MHz): d = 20.9 (SCH3), 123.6, 139.2,
220.9 (C=S).
2-Methoxy-dithiobenzoic Acid Methyl Ester (3k)32
Yield: 68%.
MS (EI): m/z (%) = 185 (16) [M+], 169 (54), 168 (49), 138 (4), 122
(100), 78 (33).
1H NMR (CDCl3, 250 MHz): d = 2.78 (s, 3 H), 3.87 (s, 3 H), 6.96–
7.00, 7.37–7.44 (2 × m, 4 H).
Anal. Calcd for C7H7NOS2 (184.99): C, 45.38; H, 3.81; N, 7.56.
Found: C, 45.43; H, 3.92; N, 7.39.
Benzenesulfonylmethyl Diethylphosphonate (6)34
1H NMR (CDCl3, 250 MHz): d = 1.26 (t, 3J = 7.0 Hz, 6 H), 3.63 (d,
2JHP = 16.0 Hz, 2 H), 4.03 (m, 4 H), 7.40–7.48 (m, 3 H), 7.85–7.96
(m, 2 H).
2-Nitro-dithiobenzoic Acid Methyl Ester (3l)
Yield: 99%; orange-brown solid; mp 62 °C.
IR (KBr): 3040, 2900, 1690, 1570, 1450, 1420, 1270, 1250, 1230,
1070, 1080, 1010 cm–1.
1H NMR (CDCl3, 400 MHz): d = 2.81 (s, 3 H, CH3S), 7.44 (dd, 3J =
7.5 Hz, 4J = 1.5 Hz, 1 H, H-4), 7.50–7.65 (m, 2 H, H-5, H-6), 7.96
(dd, 3J = 7.5 Hz, 4J = 1.4 Hz, 1 H, H-3).
13C {1H} NMR (CDCl3, 62.9 MHz): d = 21.0 (CH3), 124.9, 128.9,
130.3, 133.1, 142.3, 146.1, 226.6 (C=S).
Diethylphosphoryl Carbodithioic Acid Methyl Ester (7)35
1H NMR (CDCl3, 250 MHz): d = 1.36 (t, 3J = 7.0 Hz, 6 H), 2.73 (s,
3 H), 4.28 (dq, 3JHH = 2JHP = 7.0 Hz, 4 H).
Synthesis 2004, No. 6, 928–934 © Thieme Stuttgart · New York

934
I. Abrunhosa et al.
PAPER
(7) Leflemme, N.; Marchand, P.; Gulea, M.; Masson, S.
Acknowledgment
Synthesis 2000, 1143.
This work was performed within the ‘PUNCHOrga’ interregional
network (Pôle Universitaire Normand de Chimie Organique). We
gratefully acknowledge financial support from the ‘Ministère de la
Recherche et des Nouvelles Technologies’, CNRS (Centre National
de la Recherche Scientifique), the ‘Région Basse-Normandie’ and
the European Union (FEDR funding) for financial support.
(8) Abrunhosa, I.; Gulea, M.; Levillain, J.; Masson, S.
Tetrahedron: Asymmetry 2001, 2851.
(9) Thiel, W.; Mayer, R. J. Prakt. Chem. 1989, 243.
(10) Lempereur, C.; Plé, N.; Turk, A.; Quéguiner, G.; Corbin, F.;
Alayrac, C.; Metzner, P. Heterocycles 1998, 48, 2019.
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Synthesis; Academic Press: London, 1994.
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Synthesis 2004, No. 6, 928–934 © Thieme Stuttgart · New York