Nitroketene dithioacetal chemistry: Synthesis of 2-alkylthio-3- nitrothiophenes from nitroketene dithioacetate and chloromethyl ketones

Article abstract of DOI:10.1021/jo9008639

(Chemical Equation Presented) An effective synthesis of highly functionalized 3-nitrothiophenes was achieved from the reaction of simple, inexpensive, and readily available dipotassium 2-nitro-1, 1-ethylyenedithiolate with α-chloromethyl ketones in toluen

Full text of DOI:10.1021/jo9008639

pubs.acs.org/joc
Alkylation of 1 with propargyl bromide furnished 4-methy-
Nitroketene dithioacetal chemistry: Synthesis of
2-alkylthio-3-nitrothiophenes from nitroketene
dithioacetate and chloromethyl ketones
lene-2-[1-nitromethylidene]-1,3-dithiolane 4 resulting from
monoalkylation followed by cyclization (route c).5 In con-
tinuation of these investigations, we considered reacting salt
1 with alkyl halides having an electrophilic carbonyl group in
a 1,2-relationship, as found in acyl methyl chlorides. Pre-
viously, Jensen and co-workers have shown that alkylation
of 1 with phenacyl bromide (2-bromo-1-phenyl-1-ethanone)
led exclusively to bis-alkylated product 2 (R = CH2COPh,
Scheme 1) when the reaction was conducted in 1:1 aq
MeOH.6 We have reinvestigated the reaction and found that
the bis-alkylation of 1 takes place exclusively even when
conducted in different solvents like 1:2 aq MeOH, toluene
with 1 mol % of tetrabutylammonium bromide (TBAB), or
DMF. In complete contrast to the above result, we have
discovered that the alkylation of 1 with phenacyl chloride (2-
chloro-1-phenyl-1-ethanone) 6a takes an unprecedented
course (route d) to provide 3-nitrothiophene 5a along with
its precursor 7 (Scheme 1). Apparently, simple change of the
leaving group from bromo to chloro in phenacyl halide
resulted in alteration of the route to deliver the 3-nitrothio-
phene 5 instead of the bis-alkylated product 2. We have
investigated the scope of the transformation and report
herein details of this study.
H. Surya Prakash Rao* and K. Vasantham
Department of Chemistry, Pondicherry University,
Pondicherry-605 014, India
hspr.che@pondiuni.edu.in
Received May 1, 2009
An effective synthesis of highly functionalized 3-ni-
trothiophenes was achieved from the reaction of simple,
inexpensive, and readily available dipotassium 2-nitro-
1,1-ethylyenedithiolate with R-chloromethyl ketones in
toluene catalyzed by tetrabutylammonium bromide
(TBAB). Thiophene formation is highly sensitive and
selective for chlorine, present as a leaving group in R-
chloromethyl ketones.
Thiophenes in general7 and 3-nitrothiophenes8 in particu-
lar have found numerous applications in pharmaceutical and
technological fields. As an example, 3-nitro-2-thiophe-
nethiol, a molecule having resemblance to the products of
the present study, is a key building block in the synthesis of
the calcium antagonist drug dilthiazem.9 2-Alkylthio-3-ni-
trothiophenes of the type 5 are useful precursors for further
synthetic manipulation, as the alkylthio group can be re-
placed by nucleophiles. The reaction of nitrothiophenes with
primary and secondary amines provides highly substituted
butadienes through ring-opening pathways.10
Nitroketene dithioacetals 2 are versatile two-carbon syn-
thons, especially useful for the construction of heterocyclic
compounds.1 They can be assembled easily from inexpensive
and readily available carbon disulfide, nitromethane, and
alkylating agents in a two-step procedure.2 The first step
involves preparation of the dipotassium 2-nitro-1,1-ethyle-
nedithiolate 1 from nitromethane, carbon disulfide, and
potassium hydroxide. We have been investigating the pro-
ducts formed from the alkylation of dipotassium salt 1 with a
variety of alkyl halides. We found that alkylation of salt 1
with simple alkyl halides in a mixture of ethanol-water
furnished bis-alkylated products, viz., 1,1-di(2-alkylthio)-2-
nitroethylenes 2 (route a, Scheme 1).3 When the alkylation
was carried out in acetonitrile with sterically hindered alkyl
halides, the major products were 4-(2-alkylthio)-2-[(Z)-1-
nitromethylidene]-1,3-dithioles 3, formed by the reaction of
two units of salt 1 with one unit of alkyl halide (route b).4
(5) Rao, H. S. P. Indian J. Chem., Sect. B 2008, 47B, 272–275.
(6) Jensen, K. A.; Buchardt, O.; Lohse, C. Acta Chem. Scand. 1967, 21,
2797–2806.
(7) (a) Batchu, C. J. Sulfur Chem. 2008, 29, 187–240.(b) Russell, R. K.
Comprehensive Heterocyclic Chemistry II; Pergamon: New York, 1996; Vol. 2,
pp 679-729. (c) Rajappa, S.; Natekar, M. V. Comprehensive Heterocyclic
Chemistry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds.; Pergamon
Press: New York, 1996; Vol. 2, pp 491-605. (d) Kagan, J. Progress in the
Chemistry of Natural Products; Springer Verlag: Vienna, Austria, 1991; Vol. 56,
p 87. (e) Gronowitz, S. The Chemistry of Heterocyclic Compounds; John Wiley
and Sons: New York, 1985; Vol. 44, pp 1-214. (f) Bohlmann, F. The Chemistry of
Heterocyclic Compounds; John Wiley and Sons: New York, 1985; Vol. 44, pp
261-324. (g) Press, J. B. Chemistry of Heterocyclic Compounds, Thiophene
and its Derivatives; Gronowitz, S., Ed.; Wiley and Sons: New York, 1985; Vol. 44,
Part 1, pp 353-456, and Vol. 44, Part 3, pp 397-502. (h) Blicke, F. F. Biological
and Pharmacological Activity of Thiophene and its Derivatives; Hartough, H.
D., Ed.; Interscience: New York, 1952; pp 29-45.
(1) (a) Metzner, P.; Thuillier, A. Sulfur Reagents in Organic Chemistry;
Academic Press: New York, 1994. (b) Kolb, M. Synthesis 1990, 171–190.
(c) Tominaga, Y.; Matsuda, Y. J. Heterocycl. Chem. 1985, 22, 937–949.
(d) Misra, N. C.; Panda, K.; Ila, H.; Junjappa, H. J. Org. Chem. 2007, 72, 1246–
1251. (e) Rao, H. S. P.; Sivakumar, S. J. Org. Chem. 2005, 70, 4524–4527. (f)
Terang, N.; Mehta, B.; Ila, H.; Junjappa, H. Tetrahedron 1998, 54, 12973–12984.
(2) (a) Hsu, A. C.-T.; Peter, O.-G.; Joseph, R. W.; Clifford, L. B. Eur. Pat. Appl.
EP 765870 1997; Chem. Abstr. 1997, 126, 263848. (b) Gompper, R.; Schaefer, H.
Chem. Ber. 1967, 100, 591–604. (c) Freund, E. Chem. Ber. 1919, 52B, 542–544.
(3) Rao, H. S. P.; Sakthikumar, L.; Shreedevi, S. Sulfur Lett. 2002, 25,
207–218.
(8) (a) Morley, J. O.; Matthews, T. P. Org. Biomol. Chem. 2006, 4, 359–
366.(b) Campaigne, E. Compr. Heterocycl. Chem., 1994, 4, 922-923. (c)
Norris, R. K. Chem. Heterocycl. Compd. 1986, 44, 523–629. (d) Magdesieva, N.
N. Adv. Heterocycl. Chem. 1970, 12, 1–41. (e) Gronowitz, S. Adv. Heterocycl.
Chem. 1963, 1, 1–124.
(9) (a) Handler, N.; Erker, T.; Lemmens-Gruber, R.; Studenik, C. R.
Arzneim. Forsch. 2007, 57, 757–761. Chem. Abstr. 2008, 148, 355766. (b)
Hashiyama, T. Med. Res. Rev. 2000, 20, 485–501.
(10) (a) Bianchi, L.; Dell’Erba, C.; Maccagno, M.; Morganti, S.; Petrillo,
G.; Rizzato, E.; Sancassan, F.; Severi, E.; Spinelli, D.; Tavani, C. ARKIVOC
2006, 7, 169–185. (b) Dell'erba, C.; Novi, M.; Petrillo, G.; Tavani, C. In Topics in
Heterocyclic Systems: Synthesis, Reactions and Properties; Attanasi, O. A.,
Spinelli, D., Eds.; Research Signpost: Trivandrum, India, 1996; Vol. 1, pp 1-12.
(4) Rao, H. S. P.; Sakthikumar, L.; Vanitha, S.; Sivakumar, S. Tetra-
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DOI: 10.1021/jo9008639
r
Published on Web 07/27/2009
J. Org. Chem. 2009, 74, 6847–6850 6847
2009 American Chemical Society

Rao and Vasantham
JOCNote
SCHEME 1. Reaction of Dipotassium Salt1 withDifferentAlkyl
Halides
SCHEME 2. Competitive Reaction between Phenacyl Chloride
6a and Phenacyl Bromide 8 with the Salt 1
TABLE 1. Reaction of Dipotassium Salt 1 with R-Chloromethyl Ket-
ones 6a-f
entry
compd
R
time, h
yield, %
1
2
3
4
5
6
5a
5b
5c
5d
5e
5f
Ph
Me
C6H5SCH2
4-MeC6H4SCH2
4-ClC6H4SCH2
4-MeC6H4OCH2
6
4
4
6
4
4
27a
67
64
56
62
36
aDihydrothiophene 7 was obtained as major product in
68%.
Treatment of salt 1 with phenacyl chloride 6a in toluene in
the presence of tetrabutylammonium bromide (TBAB) as a
phase transfer catalyst (PTC) provided 3-nitrothiophene 5a
(27%) and its precursor, the dihydrothiophene 7 (68%).
There was no trace of bis-alkylated product 2 (R =
CH2COPh). The microwave-mediated dehydration of dihy-
drothiophene 7 with p-toluenesulfonic acid adsorbed over
silica gel furnished a quantitative yield of 5a. The structure of
5a was determined by spectral (IR, 1H NMR, 13C NMR, 2D
NMR, and MS) and analytical data. Characteristic singlets
for C2H of the thiophene ring and SCH2 appeared at δ 7.44
and 5.06 ppm, respectively. Supporting the assigned struc-
ture, the 13C NMR spectrum displayed 14 lines with methy-
lene carbon located at 43.5 ppm. We have conducted a
competition reaction in which salt 1 was treated with 2 molar
equiv each of phenacyl chloride 6a and phenacyl bromide 8
to determine if 3-nitrothiophene product is formed in pre-
ference (Scheme 2). This reaction furnished bis-alkylated
product 2a as the major product in 77% yield. The thiophene
5a (3%) and its precursor 7 (17%) were minor products. It
became obvious from this experiment that phenacyl bromide
is more reactive toward alkylation of 1 and the reaction takes
route a (Scheme 1) to provide the bis-alkylated product.
The reaction of salt 1with 1-chloroacetone 6b furnished1-[(4-
methyl-3-nitrothiophen-2-yl)thio]propan-2-one 5b exclusively
and there was no trace of its precursor of type 7 (Scheme 1,
Table 1). We have used this reaction as a test case to optimize
conditions for 3-nitrothiophene formation. Initially, equiva-
lents of 1-chloroacetone 6b were varied from 0.5 to 2 to find out
if the reaction takes a different course when there was change in
the concentration of the alkylating agent. We found that there
was no trace of 2:1 adduct of type 3or 1:2 adduct of type 2under
these conditions. As anticipated from structure 5 the reaction
required 2 equiv of 6b for best yield of 5b. The transformation
worked well in nonpolar solvent (toluene, 67%) in the presence
of PTC compared to polar aprotic solvent (DMF, 54%) or
polar protic solvent (1:1 aq MeOH, 43%). It is to be noted that
1:1 aq methanol was found to be the best solvent for bis-
alkylation to obtain nitroketene dithioacetals of type 2.3
SCHEME 3. Mechanism for the Formation of 3-Nitrothio-
phenes 5
The transformation of salt 1to 3-nitrothiophenes 5proved to
be general. We reacted salt 1 with different acylmethyl chlorides
6c-f under optimized conditions and in all cases 3-nitrothio-
phenes 5c-f were obtained exclusively (Table 1). Comparison
of results from the reaction of salt 1 with phenacyl chloride 6a
and 1-chloro-3-(phenylthio)propan-2-one 6c reveals that while
in the first case dihydrothiophene 7 was the major product, in
the later case 3-nitrothiophene 5c was the exclusive product.
This result indicates that antiperiplanar orientation for C4OH
and C5H in 7 for dehydration is difficult to achieve.
A possible mechanism for the 3-nitrothiophene 5 formation
is given in Scheme 3. First alkylation of salt 1with chloromethyl
ketone 6 furnishes intermediate monoalkylated product 9,
which undergoes intramolecular nitroaldol condensation to
provide 10 and 11. Second alkylation of 11 followed by
dehydration furnishes nitrothiophene 5. Posteriori, we think
that the second alkylation of the sulfanion in 9 with acyl alkyl
chlorides is slow and therefore the intermediate has sufficient
time to undergo nitro-aldol condensation. When alkylation
was conducted with phenacyl bromide, first and second alkyla-
tions were fast to provide bis-alkylated products.
6848 J. Org. Chem. Vol. 74, No. 17, 2009

Rao and Vasantham
JOCNote
SCHEME 4. Reaction of Dipotassium Salt 1 with 1-Bromoa-
cetone 12
of freshly prepared dipotassium 2-nitro-1,1-ethylenedithiolate 1
(1 g, 4.71 mmol) in distilled toluene (10 mL) at 0 °C was added
tetrabutylammonium bromide (TBAB; 0.1 mol %) in catalytic
amount as a phase transfer catalyst. To this suspension was
added a dilute solution of 1-chloroacetone 6b (9.42 mmol) in
distilled toluene (20 mL) by using a pressure equalizer funnel
during 45 min. The resulting reaction mixture was then stirred
vigorously at rt for 4 h. After the completion of the reaction
(TLC; hexanes-EtOAc 8:2), the mixture was transferred into a
beaker containing 20 g of crushed ice. The acidic (pH 5) reaction
mixture was carefully neutralized with 0.1 N NaHCO3 aqueous
solution. The contents of the reaction mixture were separated
into two phases on addition of dichloromethane (45 mL). The
organic layer was washed with water (3 ꢀ 25 mL) and brine (2 ꢀ
15 mL) and dried over anhydrous Na2SO4. Evaporation of the
solvent under reduced pressure resulted in the crude product as a
dark brown pasty mass. The crude product was purified by
column chromatography on silica gel with use of increasing
amounts of EtOAc (5% to 40%) in hexanes as eluent. Evapora-
tion of the pooled fractions furnished 0.80 g of 5b in 67% yield as
yellow crystals after recrystallization (CCl4). Mp 124-126 °C
(CCl4); Rf 0.48 (hexanes-EtOAc 8:2); UV λmax (MeOH) 373
(log ε = 4.08), 278 (log ε = 4.53), 252 (log ε = 4.62), 228 nm (log
ε = 4.82); IR (KBr) νmax 1710, 1544, 1485, 1355, 1315 cm-1; 1H
NMR (400 MHz; CDCl3) δ 6.80 (s, 1H), 3.91 (s, 2H), 2.47 (s,
3H), 2.37 (s, 3H); 13C NMR (100 MHz; CDCl3) δ 200.8 (C),
146.7 (C), 142.6 (C), 135.4 (C), 118.8 (CH), 45.7 (CH2), 28.6
(CH3), 17.4 (CH3); HRMS (ESIþ) calcd for C8H9NNaO3S2
(MNaþ) 253.9922, found 253.9919. Anal. Calcd for
C8H9NO3S2: C, 41.54; H, 3.92; N, 6.06; S, 27.73. Found: C,
41.51; H, 3.89; N, 6.05; S, 27.76.
2-[(3-Nitro-4-phenylthiophen-2-yl)thio]-1-phenylethanone, 5a:
Following the representative procedure described above, the
reaction of dipotassium 2-nitro-1,1-ethylenedithiolate 1 (1.50 g,
7.0 mmol) with phenacyl chloride 6a (2.18 g, 14.1 mmol) in
toluene (45 mL) and in the presence of a catalytic amount of
TBAB (0.023 g, 0.1 mol %) at 0 °C for 1 h was stirred at rt for 6 h.
The reaction provided 5a and 7 after separation by column
chromatography with use of increasing amounts of EtOAc (5%
to 60%) in hexanes. Compound 5a was obtained as a light yellow
solid in 0.72 g (27%) yield. Mp 180-182 °C (50% hexanes-
DCM); Rf 0.68 (hexanes-EtOAc 6:4); UV (MeOH) λmax 411 (log
ε = 3.66), 238 nm (log ε = 3.98); IR (KBr) νmax 1679, 1623, 1492,
1319, 750, 688 cm-1; 1H NMR (400 MHz; DMSO-d6) δ 8.07 (d,
J = 7.6 Hz, 2H), 7.70 (t, J = 7.2Hz, 1H), 7.57 (t, J = 7.6 Hz, 2H),
7.47 (s, 1H), 7.37-7.23 (m, 5H), 5.06 (s, 2H); 13C NMR δ
(100 MHz; DMSO-d6) 193.6 (C), 148.2 (C), 141.4 (C), 138.0
(C), 135.6 (C), 134.7 (CH), 134.6 (C), 129.4 (2 ꢀ CH), 129.0 (2 ꢀ
CH), 128.7 (2 ꢀ CH), 128.6 (2 ꢀ CH), 128.4 (CH), 123.7 (CH),
43.5 (CH2); HRMS (ESIþ) calcd for C18H13NNaO3S2 (MNaþ)
378.0235, found 378. 0243. Anal. Calcd for C18H13NO3S2: C,
60.83;H, 3.69; N, 3.94; S, 18.04. Found:C, 60.79;H, 3.66; N, 3.88;
S, 17.99.
SCHEME 5. Reaction of Dipotassium Salt 1 with 2-Chlorocy-
clohexanone 14
SCHEME 6. Reaction of Dipotassium Salt 1 with 1,3-Dichloro-
acetone 15
Indeed, this surmise was supported by the reaction be-
tween salt 1 and 1-bromoacetone 12 in solvents like toluene,
DMF, or 1:1 aq MeOH (Scheme 4). In all the runs, this reac-
tion furnished a diastereomeric mixture of 1-[(4SR,5RS)-
5-hydroxy-5-methyl-2-(nitromethylidene)-1,3-dithian-4-yl]-
ethanone 13 exclusively. The dithiane was formed by
bis-alkylation followed by intramolecular aldol condensation.
Next, we reacted salt 1 with 2-chlorocyclohexanone
14 under optimized conditions. This reaction provided
1,3-dithiole, 2-{[2-(nitromethylidene)-1,3-dithiol-4-yl]thio}-
cyclohexanone 3a in modest yield (Scheme 5). This type 3
product (route b, Scheme 1) was formed by the reaction of
2 mol of salt with 1 mol of sterically demanding alkyl halide,
namely, 2-chlorocyclohexanone 14.
Finally, we reacted salt 1 with 1,3-dichloracetone 15 and
this reaction provided 2-(nitromethylidene)-1,3-dithian-5-
one 16 (Scheme 6) as the only product in moderate yield.
This reaction obviously was going through the bis-alkylation
mode to provide product of type 2 (route a, Scheme 1).
In conclusion, we have demonstrated an unprecedented
facile two-step synthesis of 2-alkylthio-3-nitrothiophenes
from simple and inexpensive starting materials like nitro-
methane, carbon disulfide, and acyl methyl chlorides. This
reaction is selective to the leaving group (Br vs. Cl) and steric
hindrance next to the acyl group. The trisubstituted thio-
phenes prepared in this study have high potential for further
modification owing to the presence of diverse functional
groups, viz., nitro, acyl, alkylthio, etc. We are presently
exploring the reactions of the carbanion generated from
the active methylene group next to the acyl group in 5 with
1,4-bifunctional reactants like 2-hydroxybenzaldehyde for
generation of 2H-chromenols incorporating a 3-nitrothio-
phene unit.
2-[(4-Hydroxy-3-nitro-4-phenyl-4,5-dihydrothiophen-2-yl)thio]-
1-phenylethanone, 7: Yield 1.7 g (68%), light yellow solid; mp
125-126 °C (MeOH); Rf:0.48 (hexanes-EtOAc 6:4); UV
(MeOH) λmax 372 (log ε = 4.60), 289 (log ε = 4.29), 244 nm
(log ε = 4.71); IR (KBr) νmax 3503, 1681, 1596, 1480, 1295, 752,
699 cm-1; 1H NMR (400 MHz; CDCl3) δ 8.00 (d, J = 7.2 Hz,
2H), 7.64 (d, J = 7.4 Hz, 2H), 7.52 (t, J = 7.9 Hz, 2H), 7.30-7.43
(m, 4H), 4.64 (s, 2H), 4.26 (s, 1H), 3.79 (d, J = 11.9 Hz, 1H), 3.44
(d, J = 11.9 Hz, 1H); 13C NMR (100 MHz; CDCl3) δ 191.4 (C),
166.9 (C), 143.1 (C), 137.6 (C), 134.9 (C), 134.4 (CH), 129.1 (2 ꢀ
CH), 129.0 (2 ꢀ CH), 128.5 (2 ꢀ CH), 128.4 (CH), 124.0 (2 ꢀ
CH), 85.7 (C), 46.3 (CH2), 41.8 (CH2); HRMS (ESIþ) calcd for
C18H15NNaO4S2 (MNaþ) 396.0340; found 396.0439. Anal.
Calcd for C18H15NO4S2: C, 57.89; H, 4.05; N, 3.75; S, 17.17.
Found: C, 57.88; H, 4.09; N, 3.71; S, 17.19.
Experimental Section
Representative Procedure: Preparation of 1-[(4-Methyl-3-ni-
trothiophen-2-yl)thio]propan-2-one, 5b: To a stirred suspension
J. Org. Chem. Vol. 74, No. 17, 2009 6849

Rao and Vasantham
JOCNote
2,20-[(2-Nitroethene-1,1-diyl)dithiodiyl]bis(1-phenylethanone),
2a: Following the representative procedure, the reaction of
dipotassium 2-nitro-1,1-ethylenedithiolate 1 (0.5 g, 2.35 mmol)
with phenacyl bromide 8 (0.93 g, 4.69 mmol) in toluene (15 mL)
and in the presence of TBAB (0.070 g, 0.1 mol %) as phase
transfer catalyst at 0 °C for 4 h furnished 0.85 g of 2a as a yellow
solid in 96% yield. Mp 174-176 °C (MeOH); (lit. mp 173-174
°C); Rf 0.68 (hexanes-EtOAc 1:1); UV (MeOH) λmax 362 nm
(log ε = 3.6); IR (KBr) νmax 1693, 1602, 1539, 1421, 1373, 806,
638 cm-1; 1H NMR (400 MHz; DMSO-d6) δ 8.06 (d, J = 6.6 Hz,
4H), 7.72-7.54 (m, 7H), 5.13 (s, 2H), 5.05 (s, 2H); 13C NMR (75
MHz; DMSO-d6) δ 192.8 (C), 192.4 (C), 161.3 (C), 135.2 (C),
134.8 (CH), 134.2 (C), 134.0 (CH), 128.9 (2 ꢀ CH), 128.8 (2 ꢀ
CH), 128.7 (2 ꢀ CH ), 128.4 (2 ꢀ CH), 127.6 (CH), 43.3 (CH2),
39.8 (CH2); HRMS (ESIþ) calcd for C18H15NNaO4S2 (MNaþ)
396.0340, found 396.0337.
1-[(4SR,5RS)-5-Hydroxy-5-methyl-2-(nitromethylidene)-1,3-
dithian-4-yl]ethanone, 13: Following the representative proce-
dure, the reaction of dipotassium 2-nitro-1,1-ethylenedithiolate
1 (0.3 g, 1.41 mmol) with 1-bromoacetone 12 (0.39 g, 2.82 mmol)
in toluene (10 mL) in the presence of TBAB (0.042 g, 0.1 mol %)
as phase transfer catalyst at 0 °C for 4 h furnished 0.19 g of 13 as
yellow solid in 55% yield. Mp 160-162 °C (MeOH); Rf 0.68
(hexanes-EtOAc 6:4); UV (MeOH) λmax 361 (log ε = 2.7), 304
nm (log ε = 3.8); IR (KBr) νmax 3439, 1703, 1520, 1438, 1310,
805, 680 cm-1; 1H NMR (400 MHz; DMSO-d6) δ 7.49 (d, J =
5.6 Hz, 1H), 5.85 (s, 1H), 4.34 (d, J = 5.2 Hz, 1H), 2.98 (s, 2H),
2.31 (s, 3H), 1.22 (s, 3H); 13C NMR (100 MHz; DMSO-d6) δ
205.0 (C), 162.9 (C), 130.3 (CH), 75.4 (C), 65.8 (CH), 45.8 (CH2),
31.7 (CH3), 23.0 (CH3); HRMS (ESIþ) calcd for
C8H11NNaO4S2 (MNaþ) 272.0027, found 272.0018. Anal.
Calcd for C8H11NO4S2: C 38.54; H, 4.45; N, 5.62; S, 25.72.
Found: C 38.49; H, 4.43; N, 5.58; S, 25.68.
solid in 31% yield. Mp 178-180 °C (MeOH); Rf 0.68 (hexanes-
EtOAc 6:4); UV (MeOH) λmax 414 nm (log ε = 4.2); IR (KBr)
ν
max 1718, 1521, 1468, 1377, 1289, 1241, 1203 cm-1; 1H NMR
(300 MHz; CDCl3/DMSO-d6) δ 7.88 (s, 1H), 7.37 (s, 1H), 4.04 (t,
1H), 2.68-2.36 (m, 3H), 2.03-1.77 (m, 5H); 13C NMR (75
MHz; CDCl3 þ DMSO-d6) δ 205.3 (C), 166.8 (C), 129.8 (CH),
126.8 (CH), 120.9 (CH), 57.82 (CH), 40.3 (CH2), 34.2 (CH2),
23.7 (CH2), 23.6 (CH2); HRMS (ESIþ) calcd for
C10H11NNaO3S3 (MNaþ) 311.9799, found 311.9791. Anal.
Calcd for C10H11NO3S3: C, 41.50; H, 3.83; N, 4.84; S, 33.24.
Found: C 41.51; H, 3.86; N, 4.83; S, 33.28.
2-(Nitromethylidene)-1,3-dithian-5-one, 16: Following the re-
presentative procedure, the reaction of dipotassium 2-nitro-1,1-
ethylenedithiolate 1 (0.32 g, 1.5 mmol) with 1,3-dichloroacetone
15 (0.38 g, 3 mmol) in toluene (10 mL) and in the presence of
TBAB (0.049 g, 0.1 mol %) as phase transfer catalyst at 0 °C for
4 h furnished 0.13 g of 16 as a yellow solid in 45% yield. Mp 81-
82 °C (MeOH); Rf 0.68 (hexanes-EtOAc 4:6); UV (MeOH)
λ
max 354 nm (log ε = 3.9); IR (KBr) νmax 1720, 1622, 1515, 1434,
1398, 1265, 854, 677 cm-1; 1H NMR (300 MHz; CDCl3) δ 7.72
(s, 1H), 2.24 (s, 2H), 2.10 (s, 2H); 13C NMR (75 MHz, CDCl3) δ
198.3 (C), 155.3 (C), 131.54 (CH), 39.30 (CH2), 38.9 (CH2);
HRMS (ESIþ) calcd for C5H5NNaO3S2 (MNaþ) 213.9609,
found 213.9607. Anal. Calcd for C5H5NO3S2: C 31.40; H,
2.64; N, 7.32; S, 33.54. Found: C, 31.38; H, 2.59; N, 7.29; S,
33.51.
Acknowledgment. H.S.P.R thanks University Grants
Commission for UGC-SAP, Department of Science and
Technology for FIST, and Council of Scientific and Indus-
trial Research (CSIR) for financial support. V.K. thanks
CSIR fora research fellowship. We thank Prof. A. Srikrishna,
IISc, Bangalore, for providing spectral data.
2-{[(2-(Nitromethylidene)-1,3-dithiol-4-yl]thio}cyclohexanone,
3a: Following the representative procedure, the reaction of
dipotassium 2-nitro-1,1-ethylenedithiolate 1 (0.5 g, 2.35 mmol)
with 2-chlorocyclohexanone 14 (0.62 g, 4.69 mmol) in toluene
(15 mL) and in the presence of TBAB (0.077 g, 1 mol %) as phase
transfer catalyst at 0 °C for 4 h furnished 0.212 g of 3a as a yellow
Supporting Information Available: General experimental
methods, additional experimental procedures, compound char-
acterization data, and copies of spectra. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
6850 J. Org. Chem. Vol. 74, No. 17, 2009