A facile one-pot synthesis of substituted pyridine-2,4(1H,3H)-diones from acyl(carbamoyl)ketene S,S-acetals

Article abstract of DOI:10.1055/s-0028-1083168

A facile and efficient one-pot synthesis of substituted pyridine-2,4(1H,3H)-diones has been developed. Subjected to N,N- dimethylformamide dimethyl acetal (DMFDMA) in N,N-dimethylformamide at 120°C, a series of acyl(carbamoyl)ketene S,S-acetals were converted into the corresponding substituted pyridine-2,4(1H,3H)-diones in high yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0028-1083168

PAPER
3411
A Facile One-Pot Synthesis of Substituted Pyridine-2,4(1H,3H)-diones from
Acyl(carbamoyl)ketene S,S-Acetals
S
ynthesisof Pyrid
u
ine-2,4(1
H
,3
n
H
)-diones hui Li,a Wenliang Li,a,b Rui Zhang,b Yang Zhou,b Dewen Dong*b
a
School of Chemistry and Environmental Engineering, Changchun University of Science and Technology, Changchun 130022,
P. R. of China
b
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, P. R. of China
Fax +86(431)85098635; E-mail: dwdong@ciac.jl.cn
Received 26 June 2008; revised 18 July 2008
we recently investigated the aldol condensation reaction
of 3-(1,3-dithiolan-2-ylidene)pentane-2,4-dione in water
and obtained both mono- and double-condensed prod-
ucts,10 which were, in turn, further used for the synthesis
Abstract: A facile and efficient one-pot synthesis of substituted py-
ridine-2,4(1H,3H)-diones has been developed. Subjected to N,N-
dimethylformamide dimethyl acetal (DMFDMA) in N,N-dimethyl-
formamide at 120 °C, a series of acyl(carbamoyl)ketene S,S-acetals
were converted into the corresponding substituted pyridine- of thiopyrano[2,3-b]thiopyran-4,5-diones via a double
formal [5+1] annulation.11 In connection with our previ-
2,4(1H,3H)-diones in high yields.
ous work and our continuing interest in the synthesis of
valuable heterocycles, we examined the reaction of
acyl(carbamoyl)ketene S,S-acetals 1 with N,N-dimethyl-
formamide dimethyl acetal. As a result, we achieved a
convenient one-pot synthesis of substituted pyridine-
Key words: annulation, N,N-dimethylformamide dimethyl acetal,
Michael addition, a-oxoketene S,S-acetals, pyridine-2,4(1H,3H)-di-
ones
Over the few past decades, the utility of a-oxoketene S,S- 2,4(1H,3H)-diones. Herein, we wish to report our results.
acetals as versatile intermediates in organic synthesis has
Substrates, acyl(carbamoyl)ketene S,S-acetals 1, were
been recognized.1 As three carbon 1,3-bielectrophilic syn-
prepared according to our published procedure.12 With a
thons, a-oxoketene S,S-acetals have been widely applied
in the synthesis of substituted and/or fused aromatic struc-
series of substrates 1a–j in hand, we then selected 2-(1,3-
dithiolan-2-ylidene)-3-oxo-N-phenylbutanamide (1a) as a
model compound to examine its behavior under different
tural frameworks by reaction with organometallic nucleo-
philes, such as Grignard reagents,2 Reformatsky
conditions.
reagents,3 organolithium reagents,4 and organocuprate re-
Thus, the reaction of 1a with N,N-dimethylformamide
dimethyl acetal (1.5 equiv) in N,N-dimethylformamide
was first attempted at room temperature. Unfortunately,
no reaction was observed as monitored by TLC. When 1a
was subjected to N,N-dimethylformamide dimethyl acetal
(1.5 equiv) in N,N-dimethylformamide at 60 °C, the reac-
tion proceeded smoothly and furnished a product, which
was characterized as (E)-5-(dimethylamino)-2-(1,3-di-
thiolan-2-ylidene)-3-oxo-N-phenylpent-4-enamide (2a)
(86% yield), on the basis of its spectral and analytical data
(Scheme 1). It was very interesting that when the reaction
of 1a with N,N-dimethylformamide dimethyl acetal
(1.5 equiv) was performed in N,N-dimethylformamide
at 120 °C, 3-(1,3-dithiolan-2-ylidene)-1-phenylpyridine-
2,4(1H,3H)-dione (3a) was obtained in 91% yield
agents.5 Also they have been extensively exploited for the
construction of five- and six-membered heterocycles by
reaction with heteronucleophiles, such as hydrazine, hy-
droxylamine, guanidine, amidines, enamines, and di-
amines.6
During the course of our studies on the chemistry of a-oxo-
ketene S,S-acetals, we successfully developed novel strat-
egies for the synthesis of highly substituted six-membered
carbocycles7 and heterocycles,8 relying upon the utiliza-
tion of alkenoylketene S,S-acetals, derived from aldol
condensation of acylketene S,S-acetals with aldehydes,9
as a five-carbon 1,5-bielectrophilic species in the formal
[5+1] annulation with various nucleophile. Considering
the synthetic importance of alkenoylketene S,S-acetals,
S
O
O
S
O
O
S
O
S
DMFDMA
DMFDMA
S
NHPh
NHPh
DMF, 60 °C
DMF, 120 °C
N
O
S
Me2N
Ph
2a
1a
3a
Scheme 1 Reaction of 1a with N,N-dimethylformamide dimethyl acetal in N,N-dimethylformamide
SYNTHESIS 2008, No. 21, pp 3411–3414
x
x.
x
x
.
2
0
0
8
Advanced online publication: 16.10.2008
DOI: 10.1055/s-0028-1083168; Art ID: F14208SS
© Georg Thieme Verlag Stuttgart · New York

3412
Y. Li et al.
PAPER
S
O
S
O
S
O
O
O
S
S
NHR
NHR
ArCHO
Ar
EtONa, EtOH
N
S
Ar
O
R
1
4
5
Scheme 2 Intramolecular anti-Michael addition reaction reported by Bi20
(Scheme 1, Table 1, entry 1). It is assumed that the forma- large number of alkaloids that have useful biological and
tion of 3a involved tandem Aldol-type condensation and pharmacological activities.14,15 In the present work, we
aza-nucleophilic vinyl substitution (SNV) reactions,13 provided a facile and efficient one-pot synthesis of substi-
which can be regarded as a formal [5+1] annulation.
tuted pyridine-2,4(1H,3H)-diones 3 from readily avail-
able acyl(carbamoyl)ketene S,S-acetals 1. It should be
noted that the pyridine-2,4(1H,3H)-dione of type 3 ob-
tained possess very rich functionality, such as a,b-unsat-
urated carbonyl and b-dicarbonyl groups, and, in
particular, the a-oxoketene S,S-acetal moiety, which may
render them extremely versatile as valuable synthons in
other transformations. For example, the characteristic 1,3-
dithiolan-2-ylidene group has the potential to be convert-
ed into thioesters,11,16 enamines,17 1,3-dithiolan-2-yl,18
and aromatic rings19 through ring-opening, reduction,
substitution, and cycloaromatization reactions, respec-
tively.
To examine the scope of the one-pot cyclization reaction,
a range of reactions of acyl(carbamoyl)ketene S,S-acetals
1 bearing various amide groups with N,N-dimethylform-
amide dimethyl acetal (1.5 equiv) was carried out in N,N-
dimethylformamide at 120 °C, and some of the results are
summarized in Table 1. It was observed that all the reac-
tions of 1b–j with N,N-dimethylformamide dimethyl ace-
tal proceeded smoothly to afford the corresponding
substituted pyridine-2,4(1H,3H)-diones 3b–j in high
yields (up to 94%). When 2-(1,3-dithiolan-2-ylidene)-N-
methyl-3-oxobutanamide was subjected to identical con-
ditions, unfortunately, no major product was obtained
from the intractable reaction mixture. The results reveal It is worth mentioning that in Bi’s recent work on anti-
that the N-aryl amide function of 1 is crucial for the pyri- Michael additions of amide anions to enones, they devel-
dine-2,4(1H,3H)-dione synthesis.
oped a regiospecific approach to tetramic acid derivatives
as shown in Scheme 2.20 They found that the varied aryl
substituents at b-position of enones 4 had a lower effect
on the anti-Michael addition. In contrast, the anti-Michael
adduct was not obtained in our present work, which sug-
gested that the character of substituents, i.e. their electron-
ic effect, at the b-position of the enone plays a crucial role
in the regioselectivity of the cyclization.21
Actually, substituted pyridine-2,4(1H,3H)-diones and
their benzo-fused derivatives represent an important class
of aza-heterocycles that are widely distributed among a
Table 1 One-Pot Synthesis of Substituted Pyridine-2,4(1H,3H)-
diones
S
O
O
O
S
In summary, a facile and efficient synthesis of pyridine-
2,4-diones starting from acyl(carbamoyl)ketene S,S-ace-
tals is described, which involves tandem Aldol-type con-
densation and aza-nucleophilic vinyl substitution (SNV,
aza-Michael addition/elimination) reactions. The simple
execution, readily available substrates, mild conditions,
high yields, and wide range of synthetic potential of the
products make this protocol very attractive.
S
DMFDMA
NHAr
DMF,120 °C
N
O
S
1
3
Ar
Entry Substrate 1 Ar
Time Product 3 Yielda
(h)
(%)
91
90
88
84
90
87
86
93
92
94
1
2
1a
1b
1c
1d
1e
1f
Ph
2.0 3a
1.5 3b
1.5 3c
2.0 3d
1.0 3e
1.5 3f
1.5 3g
All reagents were purchased from commercial sources and used
without treatment, unless otherwise indicated. The products were
4-MeC6H4
1
purified by column chromatography over silica gel. H NMR and
3
2-MeC6H4
13C NMR spectra were recorded at 500 MHz and 125 MHz, respec-
tively, with TMS as internal standard at 25 °C on a Varian Inova-
500 spectrometer. IR spectra (KBr) were recorded on a Magna-560
FTIR spectrophotometer in the range of 400–4000 cm–1. Elemental
analyses were conducted on a PE-2400 analyzer (Perkin-Elmer).
Petroleum ether (PE) used was the fraction boiling in the range 60–
90 °C. Selected data are given for compounds 3a–j
4
2,4-Me2C6H3
4-MeOC6H4
2-MeOC6H4
2,5-MeO2C6H3
5
6
7
1g
1h
1i
8
2-MeO-5-ClC6H3 1.5 3h
3-(1,3-Dithiolan-2-ylidene)-1-phenylpyridine-2,4(1H,3H)-dione
(3a); Typical Procedure
To a soln of 1a (2.0 mmol) in DMF (10 mL) was added DMFDMA
(3.0 mmol) in one portion at r.t. under stirring. The mixture was
heated to 120 °C and stirred for 2.0 h. When the substrate 1a had
been consumed (monitored by TLC), the mixture was poured into
9
4-ClC6H4
2-ClC6H4
1.5 3i
1.0 3j
10
1j
a Isolated yield.
Synthesis 2008, No. 21, 3411–3414 © Thieme Stuttgart · New York

PAPER
Synthesis of Pyridine-2,4(1H,3H)-diones
3413
sat. aq NaCl (50 mL). The mixture was extracted with CH2Cl2
(3 × 20 mL), and the combined organic phases were washed with
H2O (3 × 20 mL), dried (MgSO4), filtered, and concentrated in vac-
uo. The crude product was purified by flash chromatography (silica
gel, PE–EtOAc, 1:3) to give 3a (91% yield) as a yellow solid; mp
222–224 °C.
1H NMR (500 MHz, CDCl3): d = 3.38–3.41 (m, 2 H), 3.43–3.45 (m,
2 H), 3.85 (s, 3 H), 5.96 (d, J = 8.5 Hz, 1 H), 6.98 (d, J = 9.0 Hz, 2
H), 7.23–7.27 (m, 3 H).
13C NMR (125 MHz, CDCl3): d = 37.5, 38.4, 55.8, 108.1, 114.8,
118.5, 128.2, 133.3, 141.9, 159.5, 162.6, 179.8, 191.5.
Anal. Calcd for C15H13NO3S2: C, 56.41; H, 4.10; N, 4.39. Found: C,
56.27; H, 4.21; N, 4.46.
IR (KBr): 3066, 1624, 1517, 1491, 1389, 1332, 1287, 1075, 910,
822, 771 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.38–3.40 (m, 2 H), 3.42–3.45 (m,
2 H), 5.98 (d, J = 8.0 Hz, 1 H), 7.26 (d, J = 8.0 Hz, 1 H), 7.34 (t,
J = 8.0 Hz, 2 H), 7.39 (t, J = 8.0 Hz, 1 H), 7.46–7.49 (m, 2 H).
3-(1,3-Dithiolan-2-ylidene)-1-(2-methoxyphenyl)pyridine-
2,4(1H,3H)-dione (3f)
Yellow solid; mp 238–240 °C.
13C NMR (125 MHz, CDCl3): d = 37.3, 38.2, 108.1, 118.2, 126.9,
128.3, 129.4, 140.2, 141.3, 162.1, 179.6, 191.5.
IR (KBr): 1630, 1576, 1500, 1429, 1398, 1325, 1280, 1256, 1015,
909, 826, 744 cm–1.
Anal. Calcd for C14H11NO2S2: C, 58.11; H, 3.83; N, 4.84. Found: C,
58.02; H, 3.92; N, 4.76.
1H NMR (500 MHz, CDCl3): d = 3.36–3.38 (m, 2 H), 3.40–3.41 (m,
2 H), 3.80 (s, 3 H), 5.93 (d, J = 8.0 Hz, 1 H), 7.01–7.05 (m, 2 H),
7.08 (d, J = 8.0 Hz, 1 H), 7.26–7.27 (m, 1 H), 7.37–7.40 (m, 1 H).
3-(1,3-Dithiolan-2-ylidene)-1-(4-tolyl)pyridine-2,4(1H,3H)-
dione (3b)
Yellow solid; mp 218–220 °C.
13C NMR (125 MHz, CDCl3): d = 37.2, 38.1, 55.8, 107.4, 112.2,
118.5, 120.8, 128.5, 129.2, 130.2, 142.4, 154.8, 162.2, 179.9, 190.7.
Anal. Calcd for C15H13NO3S2: C, 56.41; H, 4.10; N, 4.39. Found: C,
56.57; H, 4.18; N, 4.51.
IR (KBr): 2904, 1627, 1576, 1512, 1391, 1326, 1288, 1108, 910,
821, 724 cm–1.
1H NMR (500 MHz, CDCl3): d = 2.39 (s, 3 H), 3.38–3.39 (m, 2 H),
3.41–3.43 (m, 2 H), 5.96 (d, J = 8.0 Hz, 1 H), 7.20 (d, J = 8.5 Hz, 2
H), 7.24 (d, J = 8.0 Hz, 1 H), 7.27 (d, J = 8.5 Hz, 2 H).
1-(2,5-Dimethoxyphenyl)-3-(1,3-dithiolan-2-ylidene)pyridine-
2,4(1H,3H)-dione (3g)
Yellow solid; mp 228–230 °C.
13C NMR (125 MHz, CDCl3): d = 21.1, 37.2, 38.1, 107.9, 118.3,
126.6, 130.0, 137.6, 138.3, 141.5, 162.2, 179.6, 191.3.
IR (KBr): 2832, 1630, 1580, 1510, 1419, 1399, 1283, 1233, 1042,
810 cm–1.
Anal. Calcd for C15H13NO2S2: C, 59.38; H, 4.32; N, 4.62. Found: C,
59.42; H, 4.44; N, 4.70.
1H NMR (500 MHz, CDCl3): d = 3.36–3.39 (m, 2 H), 3.41–3.44 (m,
2 H), 3.76 (s, 3 H), 3.78 (s, 3 H), 5.94 (d, J = 8.0 Hz, 1 H), 6.84 (d,
J = 2.5 Hz, 1 H), 6.94–6.97 (m, 2 H), 7.09 (d, J = 8.0 Hz, 1 H).
3-(1,3-Dithiolan-2-ylidene)-1-(2-tolyl)pyridine-2,4(1H,3H)-
dione (3c)
Yellow solid; mp 183–185 °C.
13C NMR (125 MHz, CDCl3): d = 37.5, 38.3, 56.1, 56.6, 107.7,
113.6, 115.2, 115.6, 118.8, 129.3, 142.5, 149.3, 153.8, 162.3, 180.1,
190.9.
IR (KBr): 3058, 1623, 1576, 1427, 1396, 1331, 1278, 907, 811, 730
cm–1.
1H NMR (500 MHz, CDCl3): d = 2.19 (s, 3 H), 3.37–3.40 (m, 2 H),
3.43–3.46 (m, 2 H), 5.97 (d, J = 8.0 Hz, 1 H), 7.10 (d, J = 8.0 Hz, 1
H), 7.20 (d, J = 7.5 Hz, 1 H), 7.23–7.33 (m, 3 H).
Anal. Calcd for C16H15NO4S2: C, 55.00; H, 4.33; N, 4.01. Found: C,
54.87; H, 4.41; N, 3.96.
1-(5-Chloro-2-methoxyphenyl)-3-(1,3-dithiolan-2-ylidene)pyri-
dine-2,4(1H,3H)-dione (3h)
Yellow solid; mp 210–212 °C.
13C NMR (125 MHz, CDCl3): d = 17.7, 37.3, 38.2, 107.9, 118.3,
127.2, 127.8, 129.1, 131.2, 135.7, 139.3, 141.3, 161.9, 179.7, 191.4.
IR (KBr): 3070, 1627, 1582, 1500, 1411, 1330, 1289, 1247, 1015,
911, 811 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.37–3.40 (m, 2 H), 3.42–3.44 (m,
2 H), 3.79 (s, 3 H), 5.94 (d, J = 8.0 Hz, 1 H), 6.95 (d, J = 9.0 Hz, 1
H), 7.04 (d, J = 8.0 Hz, 1 H), 7.28 (d, J = 2.5 Hz, 1 H), 7.34–7.36
(dd, J1 = 9.0 Hz, J2 = 2.5 Hz, 1 H).
Anal. Calcd for C15H13NO2S2: C, 59.38; H, 4.32; N, 4.62. Found: C,
59.25; H, 4.20; N, 4.75.
1-(2,4-Dimethylphenyl)-3-(1,3-dithiolan-2-ylidene)pyridine-
2,4(1H,3H)-dione (3d)
Yellow solid; mp 169–171 °C.
13C NMR (125 MHz, CDCl3): d = 37.5, 38.4, 56.4, 108.0, 113.5,
IR (KBr): 2920, 1626, 1579, 1505, 1425, 1404, 1326, 1280, 1257,
818 cm–1.
1H NMR (500 MHz, CDCl3): d = 2.14 (s, 3 H), 2.36 (s, 3 H), 3.36–
3.40 (m, 2 H), 3.42–3.45 (m, 2 H), 5.96 (d, J = 8.0 Hz, 1 H), 7.06–
7.11 (m, 3 H), 7.14 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = 17.6, 21.1, 37.3, 38.1, 107.8,
118.3, 127.5, 127.8, 131.8, 135.3, 136.7, 139.0, 141.6, 162.1, 179.8,
191.3.
118.4, 125.5, 129.5, 129.7, 130.2, 142.0, 153.9, 162.1, 179.9, 191.3.
Anal. Calcd for C15H12ClNO3S2: C, 50.92; H, 3.42; N, 3.96. Found:
C, 51.13; H, 3.37; N, 4.07.
1-(4-Chlorophenyl)-3-(1,3-dithiolan-2-ylidene)pyridine-
2,4(1H,3H)-dione (3i)
Yellow solid; mp 231–233 °C.
IR (KBr): 1624, 1574, 1489, 1395, 1287, 1255, 1089, 1015, 910,
818, 760 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.40–3.42 (m, 2 H), 3.43–3.45 (m,
2 H), 5.99 (d, J = 8.0 Hz, 1 H), 7.22 (d, J = 8.0 Hz, 1 H), 7.29 (d,
J = 8.0 Hz, 2 H), 7.45 (d, J = 8.0 Hz, 2 H).
13C NMR (125 MHz, CDCl3): d = 37.3, 38.2, 108.5, 118.0, 128.2,
129.5, 134.1, 138.6, 140.7, 162.0, 179.4, 191.9.
Anal. Calcd for C16H15NO2S2: C, 60.54; H, 4.76; N, 4.41. Found: C,
60.39; H, 4.85; N, 4.50.
3-(1,3-Dithiolan-2-ylidene)-1-(4-methoxyphenyl)pyridine-
2,4(1H,3H)-dione (3e)
Yellow solid; mp 238–240 °C.
IR (KBr): 2907, 1628, 1575, 1510, 1401, 1323, 1289, 1241, 1026,
817 cm–1.
Synthesis 2008, No. 21, 3411–3414 © Thieme Stuttgart · New York

3414
Y. Li et al.
PAPER
(5) (a) Dieter, R. K.; Silks, L. A.; Fishpaugh, J. R.; Kastner,
Anal. Calcd for C14H10ClNO2S2: C, 51.93; H, 3.11; N, 4.33. Found:
C, 51.81; H, 3.19; N, 4.42.
M. E. J. Am. Chem. Soc. 1985, 107, 4679. (b) Dieter, R. K.;
Fishpaugh, J. R.; Silks, L. A. Tetrahedron Lett. 1982, 23,
3751.
1-(2-Chlorophenyl)-3-(1,3-dithiolan-2-ylidene)pyridine-
2,4(1H,3H)-dione (3j)
Yellow solid; mp 199–201 °C.
(6) (a) Mahata, P. K.; Venkatesh, C.; Kumar, U. K. S.; Ila, H.;
Junjappa, H. J. Org. Chem. 2003, 68, 3966. (b) Rudorf,
W.-D. Tetrahedron 1978, 34, 725. (c) Chauhan, S. M. S.;
Junjappa, H. Tetrahedron 1976, 32, 1779. (d) Chauhan,
S. M. S.; Junjappa, H. Tetrahedron 1976, 32, 1911.
(e) Apparao, S.; Rahman, A.; Ila, H. Synthesis 1982, 792.
(f) Singh, L. W.; Gupta, A. K.; Ila, H.; Junjappa, H. Synthesis
1984, 516. (g) Barun, O.; Ila, H.; Junjappa, H. J. Org. Chem.
2000, 65, 1583.
(7) Bi, X.; Dong, D.; Liu, Q.; Pan, W.; Zhao, L.; Li, B. J. Am.
Chem. Soc. 2005, 127, 4578.
(8) (a) Dong, D.; Bi, X.; Liu, Q.; Cong, F. Chem. Commun.
2005, 35802. (b) Bi, X.; Dong, D.; Li, Y.; Liu, Q.; Zhang, Q.
J. Org. Chem. 2005, 70, 10886.
IR (KBr): 1627, 1577, 1541, 1479, 1423, 1397, 1371, 1246, 1155,
1054, 813, 760 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.38–3.41 (m, 2 H), 3.43–3.46 (m,
2 H), 6.00 (d, J = 8.0 Hz, 1 H), 7.07 (d, J = 8.5 Hz, 1 H), 7.36–7.41
(m, 3 H), 7.38–7.56 (m, 1 H).
13C NMR (125 MHz, CDCl3): d = 37.3, 38.2, 108.1, 118.0, 127.9,
129.9, 130.3, 130.5, 132.4, 137.5, 140.9, 161.7, 179.6, 191.6.
Anal. Calcd for C14H10ClNO2S2: C, 51.93; H, 3.11; N, 4.33. Found:
C, 51.78; H, 3.06; N, 4.21.
(E)-5-(Dimethylamino)-2-(1,3-dithiolan-2-ylidene)-3-oxo-N-
phenylpent-4-enamide (2a)
Yellow solid; mp 198–200 °C.
(9) (a) Myrboh, B.; Asokan, C. V.; Ila, H.; Junjappa, H.
Synthesis 1984, 50. (b) Asokan, C. V.; Ila, H.; Junjappa, H.
Synthesis 1985, 163. (c) Asokan, C. V.; Balu, M. P.; Ila, H.;
Junjappa, H. Synthesis 1988, 727. (d) Choi, E. B.; Youn,
I. K.; Pak, C. S. Synthesis 1991, 15.
IR (KBr): 2923, 1630, 1541, 1491, 1440, 1417, 1354, 1322, 1265,
1177, 1088, 758 cm–1.
(10) Ouyang, Y.; Dong, D.; Pan, W.; Zhang, J.; Liu, Q.
Tetrahedron 2006, 62, 10111.
(11) Pan, W.; Dong, D.; Ouyang, Y.; Wu, R.; Yang, Y.; Liu, Q.
Synthesis 2007, 2115.
1H NMR (500 MHz, CDCl3): d = 2.89 (s, 3 H), 3.15 (s, 3 H), 3.31–
3.35 (m, 4 H), 5.49 (d, J = 12.5 Hz, 1 H), 7.05 (t, J = 7.5 Hz, 1 H),
7.29 (t, J = 7.5 Hz, 2 H), 7.60 (d, J = 7.5 Hz, 2 H), 7.69 (d, J = 12.5
Hz, 1 H), 9.60 (s, 1 H).
13C NMR (125 MHz, CDCl3): d = 36.3, 37.7, 38.5, 45.2, 93.5,
120.1, 124.1, 126.2, 129.3, 139.8, 153.8, 159.8, 166.8, 181.4.
(12) Ouyang, Y.; Dong, D.; Yu, H.; Liang, Y.; Liu, Q. Adv. Synth.
Catal. 2006, 348, 206.
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(c) Bernasconi, C. F.; Ketner, R. J.; Chen, X.; Rappoport, Z.
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M. J. Org. Chem. 1989, 54, 5853. (e) Baldwin, J. E.;
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Anal. Calcd for C16H18N2O2S2: C, 57.46; H, 5.42; N, 8.38. Found:
C, 57.39; H, 5.50; N, 8.24.
Acknowledgement
Financial support of this research by the National Natural Science
Foundation of China (20572013 and 20711130229), the Ministry of
Education of China (105061) and the Department of Science and
Technology of Jilin Province (20050309) is greatly acknowledged.
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Synthesis 2008, No. 21, 3411–3414 © Thieme Stuttgart · New York