Efficient and practical route to α-aminocarbonylketene and α-cyanoketene dithioacetals

Article abstract of DOI:10.1080/00397910601131379

An efficient and practical route to α-aminocarbonylketene dithioacetals 5 and α-cyanoketene dithioacetals 6 was developed. With readily available α-acetyl-α-aminocarbonyl ketene dithioacetals 4 as the starting materials, α-aminocarbonylketene dithioacetal

Full text of DOI:10.1080/00397910601131379

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Efficient and Practical Route to
α‐Aminocarbonylketene and α‐Cyanoketene
Dithioacetals
Yanbing Yin a b , Qian Zhang a , Qun Liu a , Yu Liu a & Shaoguang Sun a
a Department of Chemistry , Northeast Normal University , Changchun,
China
b Department of Chemistry and Chemical Engineering , Qiqihar University ,
Qiqihar, China
Published online: 10 Mar 2007.
To cite this article: Yanbing Yin , Qian Zhang , Qun Liu , Yu Liu & Shaoguang Sun (2007) Efficient and
Practical Route to α‐Aminocarbonylketene and α‐Cyanoketene Dithioacetals, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:5, 703-711, DOI:
10.1080/00397910601131379
To link to this article: http://dx.doi.org/10.1080/00397910601131379
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Synthetic Communicationsw, 37: 703–711, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601131379
Efficient and Practical Route
to a-Aminocarbonylketene and
a-Cyanoketene Dithioacetals
Yanbing Yin
Department of Chemistry, Northeast Normal University, Changchun,
China and Department of Chemistry and Chemical Engineering, Qiqihar
University, Qiqihar, China
Qian Zhang, Qun Liu, Yu Liu, and Shaoguang Sun
Department of Chemistry, Northeast Normal University, Changchun,
China
Abstract: An efficient and practical route to a-aminocarbonylketene dithioacetals
5 and a-cyanoketene dithioacetals 6 was developed. With readily available
a-acetyl-a-aminocarbonyl ketene dithioacetals
4 as the starting materials,
a-aminocarbonylketene dithioacetals 5 were prepared in high yield via base-
catalyzed (sodium hydroxide) deacetylation. In the presence of POCl3 and with
DMF as the solvent, a-cyanoketene dithioacetals 6 were obtained via dehydration of
5 in excellent yield.
Keywords: a-acetyl-a-aminocarbonyl ketene dithioacetals, a-aminocarbonylketene,
a-cyanoketene dithioacetals, deacetylation, dehydration, dithioacetals
Over the past decades, the utility of a-functionalized ketene dithioacetals
as versatile intermediates in organic synthesis has been recognized.[1–3]
As part of our studies in this field,[4] recently we became interested in
Received June 20, 2006
Address correspondence to Qian Zhang, Department of Chemistry, Northeast
Normal University, Changchun 130024, China. E-mail: zhangq651@nenu.du.cn
or Qun Liu, liuqun@nenu.edu.cn
703

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Y. Yin et al.
the C-C bond-forming reactions of the polarized ketene dithioacetals toward
carbon nucleophiles at their a-position and the reactions of a-acetylketene
dithioacetal 1 with reactive arylaldehydes[5a] or 1 with reactive arylalde-
hydes[5a] or with respective arylaldehydes nitriles[5b] to give the double
Morita–Baylis–Hilman type adducts 2 and aza-Mortia–Baylis–Hillman
type adducts 3 (Scheme 1), respectively, were reported. In continuing the
research, the ketene dithioacetals with different electron-withdrawing groups
(EWG) on the a-position were examined for their efficiency in the C-C
bond-forming reactions. Thus, the a-cyanoketene dithioacetals with the
structure of 6 (Scheme 2) was chosen, because unsaturated nitriles can be
expected to show interesting properties in organic synthesis.[6]
To our knowledge, there are few reports about the synthesis of a-cyano-
ketene dithioacetals with the structure of 6 (Scheme 2). Among these reported,
the reactions of the condensation on the lithium salt of acetonitrile with
dimethyl trithiocarbonate followed by alkylation [Eq. (1)][7a] and the reaction
of the cyanotrimethylammonium ylid with dialkyl trithiocarbonate [Eq. (2)][7b]
were involved. Intrinsic drawbacks, however, such as the low[7a] or unsatisfac-
tory yield (50–58%),[7b] moisture-sensitive reaction conditions, and the use of
a separate step for dialkyl trithiocarbonate[7a,7b] or cyanotrimethylammonium
methylid[7b] preparation severely limit their application. On the other hand,
although the route via the saponification of 3,3-bis(alkylthio)-2-ethoxycarbony-
lacrylonitrile and subsequent decarboxylation [Eq. (3)] is simple, it suffers from
the unspecified product yields.[7c] According to our previous works,[8] the com-
mercially available double-activated ketene dithioacetals (with two EWG at the
a-position) were selected as the substrates. The substrates a-acetyl-a-aminocar-
bonyl ketene dithioacetals 4a–4e were prepared in 78–85% yields according to
the literature method.[9] Thus, starting from a-acetyl-a-aminocarbonyl ketene
dithioacetals 4 (Scheme 2), a series of a-aminocarbonylketene dithioacetals 5
and a-cyanoketene dithioacetals 6 were synthesized, respectively, in high to
excellent yields under mild reaction conditions. The results are described in
this communication.
In the beginning of this study, the saponification of 3,3-bis(methylthio)-2-
methoxycarbonylacrylonitrile and subsequent decarboxylation method[7c] was
reexamined. The results showed that this method did afford the desired
product, a-cyanoketene dimethylthioacetal 6a, but in an unspecified yield
Scheme 1.

a-Aminocarbonylketene and a-Cyanoketene Dithioacetals
705
Scheme 2. Synthesis of a-aminocarbonyl 5 and a-cyanoketene dithioacetals 6.
(in the range of 20–50%) because both cyano and methoxycarbonyl groups
are sensitive under basic conditions. In fact, amide functionality is more
stable than methoxycarbonyl, acetyl, or cyano group to bases and can
undergo dehydration to the cyano group by a dehydration reagent. The deace-
tylation and dehydration sequence was then designed with the easily available
a-acetyl-a-aminocarbonyl ketene dithioacetals 4 as the substrates. As a probe
experiment, the deacetylation reaction of 2-(bis(methylthio)methylene)-3-
oxobutanamide, substrate 4a, was investigated at first. The reaction
completed after the mixture of a 4a (410 mg, 2.0 mmol) and NaOH
(160 mg, 4.0 mmol) in acentonitrile (10 mL) was heated at reflux temperature
for 30 min (monitored by thin-layer chromatography, TLC), and then the
reaction mixture was poured into cold water (10 mL) and stirred for another
30 min. Pure 3,3-bis(methylthio)acrylamide, product 5a, was obtained as a
light yellow solid in 80% yield simply by filtration. Under identical conditions
as those described previously a-aminocarbonylketene dithioacetals 5b–5e
were obtained in high yields (Table 1).
With the easily available a-aminocarbonyl ketene dithioacetals at hand, our
attention was then turned to their dehydration reaction to prepare the correspond-
ing a-cyanoketene dithioacetals 6, and POCl3 was adopted as the dehydration
reagent.[10] As a result, the dehydration reaction occurred very fast. For
example, to the solution of a-aminocarbonyl ketene dithioacetal 5a (326 mg,

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Y. Yin et al.
Table 1. Prepared a-aminocarbonylketene dithioacetals 5
and a-cyanoketene dithioacetals 6
Yield (%)
Product
5, 6
R
5
6
a
b
c
d
e
CH3
80
78
88
85
78
95
92
95
93
90
CH3CH2
(CH2)2
(CH2)3
C6H5CH2
2.0 mmol) in 10 mL of DMF, POCl3 (0.26 mL, 2.4 mmol) was added dropwise
within 5 min under stirring at room temperature, and the reaction mixture was
stirred for another 5 min at room temperature to completion (monitored by
TLC). Then the reaction mixture was poured into cold water (10 mL) and
stirred for 10 min. Pure 3,3-bis(methylthio)acrylonitrile, product 6a, was
obtained as a white crystal in 95% yield simply by filtration. Under identical con-
ditions as those described previously, a-cyanoketene dithioacetals 6c–6e were
obtained in nearly quantitative yield (Table 1). Compound 6b, a liquid
product, was obtained by extracting the reaction mixture with dichloromethane
(10 mL ꢀ 2), washing with water, drying over anhydrous magnesium sulfate,
and then evaporating the solution (Table 1).
In our experiments, we found that when 1.5 equiv. POCl3 to 6c was added,
a product, 2-(1,3-dithiolan-2-ylidene)-3-oxopropanenitrile 7c, was obtained in
95% yield. A similar result was also reported by Anabha and coworkers.[11]
In conclusion, we have demonstrated a facile method for the preparation
of a-aminocarbonyl and a-cyanoketene dithioacetals. Some advantages, such
as the readily available substrates and reagents, mild reaction conditions, and
high yields, make this method attractive. The potential synthetic applications
of a-cyanoketene dithioacetals are being explored (Scheme 3).
EXPERIMENTAL
All reagents were commercial and were used without further purification. The
a-acetyl-a-aminocarbonyl ketene dithioacetals 4a–4e were prepared via a
Scheme 3. Synhesis of 2-(1,3-dithiolan-2-ylidene)-3-oxopropanenitrille.

a-Aminocarbonylketene and a-Cyanoketene Dithioacetals
707
known procedure.[9] Anhydrous MgSO4 was used as drying agent. Melting
1
points are uncorrected. The H NMR and 13C spectra were determined on a
Varian Unity spectrometer (500 MHz) in CDCl3 with TMS as internal
standard. IR (KBr) spectra were measured using a Magna-IR 560 spectro-
meter. Mass spectra were recorded on Agilient 1100 LCMsD spectrometer.
Elemental analyses were obtained on a PE-2400 analyser.
General Procedure
General Procedure for 5
The corresponding compound 4 (20 mmol) was added to a solution of sodium
hydroxide (40 mmol) in acetonitrile (100 mL). The mixture was refluxed for
30 min (monitored by TLC), and then the reaction mixture was poured into
cold water (100 mL) and stirred for another 30 min. Pure a-aminocarbonylk-
etene dithioacetals 5 was obtained as a solid simply by filtration.
Data
1
5a. Yield 80%; light yellow solid; mp 128–1308C; H NMR (500 MHz,
CDCl3) d: 2.38 (s, 3H, SCH3), 2.47 (s, 3H, SCH3), 5.61 (s, 1H, C55CH),
5.78 (broad, 2H, NH2); 13C NMR (125 MHz, CDCl3) d: 14.82, 16.03,
109.19, 154.69, 165.74; IR (KBr, cm21): 3347, 2997, 2881, 1643, 1523,
1383, 1264; MS (EI) m/z 164 [(M þ 1)]þ; anal. calcd. for C5H9NOS2: C,
36.78; H, 5.56; N, 8.58. Found: C, 36.86; H, 5.68; N, 8.42.
5b. Yield 78%; pale brown solid; mp 100–1028C; 1H NMR (500 MHz,
CDCl3) d: 1.31–1.35 (m, 6H, CH3), 2.86 (q, 2H, J ¼ 7.5 Hz, SCH2), 3.01
(q, 2H, J ¼ 7.5 Hz, SCH2), 5.52 (broad, 1H, NH), 5.86 (s, 1H, C55CH),
6.54 (broad, 1H, NH); 13C NMR (125 MHz, CDC13) d: 13.14, 14.92,
28.14, 28.28, 116.65, 150.89, 166.69; IR (KBr, cm21): 3389, 3186, 2928,
1636, 1539, 1380, 1274; MS (EI) m/z 192 [(M þ l)]þ; anal. calcd. for
C7H13NOS2: C, 43.95; H, 6.85; N, 7.32. Found: C, 44.08; H, 6.77; N, 7.25.
5c. Yield 88%; pale brown solid; mp 162–1648C; 1H NMR (500 MHz,
CDC13) d: 3.34 (t, 2H, J ¼ 6.0 Hz, SCH2), 3.42 (t, 2H, J ¼ 6.0 Hz,
SCH2), 5.22 (broad, 2H, NH2), 6.08 (s, 1H, C55CH); 13C NMR
(125 MHz, CDC13) d: 35.74, 38.92, 104.78, 161.73, 167.28; IR (KBr,
cm21): 3391, 3168, 1638, 1553, 1386, 1266; MS (EI) m/z 162
[(M þ l)]þ; anal. calcd. for C5H7NOS2: C, 37.24; H, 4.38; N, 8.69. Found:
C, 37.15; H, 4.49; N, 8.58.
5d. Yield 85%; pale brown solid; mp 154–1568C; 1H NMR (500 MHz,
CDCl3) d: 2.18–2.21 (m, 2H, CH2), 2.95–2.99 (m, 4H, SCH2), 5.38

708
Y. Yin et al.
(broad, 2H, NH2), 6.11 (s, 1H, C55CH); 13C NMR (125 MHz, CDCl3)
d: 23.82, 28.14, 28.77, 114.80, 156.68, 166.85; IR (KBr, cm21): 3395,
3208, 1652, 1540, 1381, 1271; MS (EI) m/z 176 [(M þ l)]þ; anal. calcd.
for C6H9NOS2: C, 41.12; H, 5.18; N, 7.99. Found: C, 41.26; H, 5.30; N, 7.91.
5e. Yield 78%; brown solid; mp 138–1408C; 1H NMR (500 MHz, CDCl3) d:
4.05 (s, 2H, CH2), 4.17 (s, 2H, CH2), 5.25 (broad, 1H, NH), 5.94 (s, 1H,
C55CH), 6.07 (broad, 1H, NH), 7.25–7.37 (m, 10 H, ArH); 13C NMR
(125 MHz, CDCl3) d: 38.77, 39.09, 119.34, 127.92, 128.08, 128.97, 129.08,
129.25, 129.27, 135.12, 136.72, 149.08, 166.29; IR (KBr, cm21): 3481,
3150, 1650, 1518, 1375, 1274, 1069; MS (EI) m/z 316 [(M þ l)]þ; anal.
calcd. for C17H17NOS2: C, 64.73; H, 5.43; N, 4.44. Found: C, 64.84; H,
5.51; N, 4.36.
General Procedure for 6
To the solution of a-aminocarbonyl ketene dithioacetal 5a (20 mmol) in
50 mL of DMF, POCl3 (24 mmol) was added dropwise within 5 min under
stirring at room temperature, and the reaction mixture was stirred for
another 5 min at room temperature (monitored by TLC). Then the reaction
mixture was poured into cold water (50 mL) and stirred for 10 min. Pure
a-cyanoketene dithioacetals 6 (except 6b) were obtained as white crystals
simply by filtration. Compound 6b, a liquid product, was obtained by
extracting the reaction mixture with dichloromethane (25 mL ꢀ 2), washing
with water, drying over anhydrous magnesium sulfate, and evaporating the
solution.
Data
6a. Yield 95%; white crystal; mp 30–328C; 1H NMR (500 MHz, CDC13) d:
2.41 (s, 3H, SCH3), 2.56 (s, 3H, SCH3), 5.02 (s, 1H, C55CH); 13C NMR
(125 MHz, CDCl3) d: 15.34, 15.97, 86.32, 115.34, 163.43; IR (KBr,
cm21): 3083, 2991, 2197, 1510, 1419, 1271, 1051, 918; MS (EI) m/z 146
[(M þ l)]þ; anal. calcd. for C5H7NS2: C, 41.35; H, 4.86; N, 9.64. Found: C,
41.48; H, 4.75; N, 9.57.
1
6b. Yield 92%; pale yellow oil; H NMR (500 MHz, CDCl3) d: 1.31–1.34
(m, 6H, CH3), 2.87 (q, 2H, J ¼ 7.5 Hz, SCH2), 3.04 (q, 2H, J ¼ 7.5 Hz,
SCH2), 5.18 (s, 1H, C55CH); 13C NMR (125 MHz, CDCl3) d: 13.12, 14.96,
28.41, 28.45, 90.74, 116.69, 162.22; IR (KBr, cm21): 2973, 2930,
2204, 1522, 1450, 1377, 1262, 1056, 920; MS (EI) m/z 174 [(M þ 1)]þ;
anal. calcd. for C7H11NS2: C, 48.51; H, 6.40; N, 8.08. Found: C, 48.63; H,
6.52; N, 8.13.

a-Aminocarbonylketene and a-Cyanoketene Dithioacetals
709
1
6c. Yield 92%; white crystal; mp 54–568C; H NMR (500 MHz, CDCl3) d:
3.55–3.59 (m, 4H, SCH2), 5.30 (s, 1H, C55CH); 13C NMR (125 MHz,
CDCl3) d: 38.31, 38.50, 80.28, 116.60, 167.38; IR (KBr, cm21): 2195,
1533, 1421, 1280, 922; MS (EI) m/z 144 [(M þ 1)]þ; anal. calcd. for
C5H5NS2: C, 41.93; H, 3.52; N, 9.78. Found: C, 42.02; H, 3.64; N, 9.85.
1
6d. Yield 93%; white crystal; mp 60–628C; H NMR (500 MHz, CDCl3) d:
2.17–2.24 (m, 2H, CH2), 2.97–3.06 (m, 4H, SCH2), 5.36 (s, 1H,
C55CH); 13C NMR (125 MHz, CDCl3) d: 22.84, 28.77, 28.87, 90.19,
116.43, 164.16; IR (KBr, cm21): 2924, 2200, 1525, 1420, 1302, 912; MS
(EI) m/z 158 [(M þ 1)]þ; anal. calcd. for C6H7NS2: C, 45.83; H, 4.49; N,
8.91. Found: C, 45.91; H, 4.56; N, 8.85.
1
6e. Yield 90%; white crystal; mp 76–788C; H NMR (500 MHz, CDCl3) d:
4.03 (s, 2H, CH2), 4.25 (s, 2H, CH2), 5.25 (s, 1H, C ¼ CH) 7.27–7.37
(m, 10H, ArH); 13C NMR (125 MHz, CDCl3) d: 38.92, 39.31, 93.95,
116.31, 128.06, 128.35, 128.93, 129.02, 129.24, 129.37, 134.32, 135.84,
160.85; IR (KBr, cm21): 2199, 1645, 1538, 1501, 1454, 1236, 1070; MS
(EI) m/z 298 [(M þ 1)]þ; anal. calcd. for C17H15NS2: C, 68.65; H, 5.08;
N, 4.71. Found: C, 68.78; H, 5.19; N, 4.68.
General Procedure for 7c
To the solution of 2-(1,3-dithiolan-2-ylidene)acetonitrile 6c (4 mmol) in 5 mL
of DMF, POCl3 (6 mmol) was added dropwise under stirring at 08C, and the
reaction mixture was stirred for 24 h at room temperature (monitored by
TLC). Then the reaction mixture was poured into a cold sat. K2CO3
solution (60 mL). The pure product 2-(1,3-dithiolan-2-ylidene)-3-oxopropa-
nenitrile 7c was obtained as a white solid simply by filtration.
Data
7c. Yield 95%; white solid; mp 116–1188C; 1H NMR (500 MHz, CDCl3) d:
3.57–3.69 (m, 4H, SCH2), 9.46 (s, 1H, CHO); 13C NMR (125 MHz, CDCl3)
d: 35.54, 39.46, 96.86, 116.00, 180.73, 180.60; IR (KBr, cm21C): 2197, 1652,
1425, 1210, 1015; MS (EI) m/z 172 [(M þ 1)]þ; anal. calcd. for C6H5NOS2:
C, 42.08; H, 2.94; N, 8.18. Found: C, 42.25; H, 3.08; N, 8.11.
ACKNOWLEDGMENTS
Financial support of this by the National Natural Science Foundation of China
(NNSFC) (20272008) and the Key Grant Project of Chinese Ministry of
Education (10412) are greatly acknowledged.

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Y. Yin et al.
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