Thia-Michael addition reactions using 2-[bis(alkylthio)methylene]-3-oxo-N- o-tolylbutanamides as odorless and efficient thiol equivalents

Article abstract of DOI:10.1055/s-2005-923602

A series of 2-[bis(alkylthio)methylene]-3-oxo-N-o-tolylbutanamides 1 have been investigated as nonthiolic and odorless thiol equivalents in thia-Michael addition reactions. The cleavage of compounds 1 is initiated by NaOH in EtOH; the in situ generated th

Full text of DOI:10.1055/s-2005-923602

LETTER
283
Thia-Michael Addition Reactions Using 2-[Bis(alkylthio)methylene]-3-oxo-N-
o-tolylbutanamides as Odorless and Efficient Thiol Equivalents
T
hia-Michael Add
e
ition Reacti
w
ons en Dong,* Haifeng Yu, Yan Ouyang, Qun Liu,* Xihe Bi, Yumei Lu
Department of Chemistry, Northeast Normal University, Changchun, 130024, P. R. of China
Fax +86(431)5098635; E-mail: dongdw663@nenu.edu.cn
Received 22 October 2005
thiol functions and applied them in umpolung chemistry.6
Abstract: A series of 2-[bis(alkylthio)methylene]-3-oxo-N-o-
tolylbutanamides 1 have been investigated as nonthiolic and odor-
less thiol equivalents in thia-Michael addition reactions. The cleav-
age of compounds 1 is initiated by NaOH in EtOH; the in situ
Limura et al described an odorless dithioester which could
be used in thioacetalization.7 Ranu et al. reported the
Michael addition of dialkyl disufides to a,b-unsaturated
generated thiolate anions undergo facile conjugate addition to a,b- carbonyl compounds catalyzed by indium(I) iodide.8
unsaturated carbonyl compounds 2 affording the corresponding b-
keto sulfides 3 in very high yields. Meanwhile, 3-oxo-N-o-tolylbu-
tanamide 4, the precursor of compounds 1, can be recovered from
the novel thia-Michael addition reactions as a byproduct in good
yield.
However, the high cost of catalysts, the multi-step prepa-
ration process, and toxicity of some precursors limit the
practical application of such thiol equivalents.
Recently, we described various ketene-S,S-acetals as
odorless dithiol equivalents in acid-promoted thio-
acetalization9 and Michael additions.10 With the expecta-
tion of obtaining odorless, efficient, and practical thiol
equivalents as well as an expansion of their applications,
we herein wish to report our investigations with 2-
[bis(alkylthio)methylene]-3-oxo-N-o-tolylbutanamides 1
(Figure 1), as thiol equivalents, in the thia-Michael
addition to a,b-unsaturated carbonyl compounds under
basic conditions.
Key words: b-keto sulfide, Michael addition, a,b-unsaturated car-
bonyl compound, a-oxo ketene-S,S-acetal, thiol equivalent
Over the last three decades, Michael addition of thiols to
a,b-unsaturated carbonyl compounds has attracted a great
deal of attention since it is one of the most convenient and
efficient methods for the construction of carbon–sulfur
bonds and it has been widely applied in organic synthe-
sis.1 Commonly, the conjugate addition is carried out un-
der either acid or base catalysis. Indeed, extensive work
has focused on the investigation of catalysts which would
result in mild reaction conditions, high selectivity, and tol-
erate a wide range of functionality.2 Recently, some envi-
ronmentally benign molten salts and room temperature
ionic liquids have been used as both efficient catalysts and
reaction media in thia-Michael addition reactions thus
avoiding organic solvents and toxic catalysts.3 However,
most of the conventional room temperature ionic liquids
are very expensive or are costly to prepare. Additionally,
it should be noted that some thiols, especially those with
low molecular weights, are highly volatile and odorous
and may lead to serious environmental and safety prob-
lems. Some attempts have been made to develop practi-
cally odorless and less volatile substitutes for the odorous
thiols used in various organic reactions by several re-
search groups. Node et. al. developed a range of odorless
or faint smelling thiols or their derivatives by increasing
the alkyl chain length or introducing a trimethylsilyl
group onto a benzene ring.4 They achieved a highly dia-
stereoselective thia-Michael addition to a,b-unsaturated
esters and amides using a complex containing a chiral
odorless thiol.5 Bertini et al. prepared odorless linear and
cross-linked copolymeric reagents with 1,3-propanedi-
O
O
N
H
RS
SR
1a R = Me, 1b R = Et, 1c R = n-Bu, 1d R = Allyl, 1e R = Bn
Figure 1
Extensive work on the synthesis and application of a-oxo
ketene-S,S-acetals has been reported elsewhere.11 The
substrates 1a–e were easily prepared from 3-oxo-N-o-
tolylbutanamide 4, CS2, and alkyl halides in the presence
of K2CO3 at room temperature in nearly quantitative
yields according to a method previously reported.12 It is
worth noting that 1a–e are all odorless yellow solids and
perfectly stable in open air.
O
SEt
O
3b
2a
NaOH, EtOH
+
+
O
O
O
O
N
H
N
H
EtS
SEt
1b
4
SYNLETT 2006, No. 2, pp 0283–0287
Advanced online publication: 23.12.2005
0
1.
0
2.
2
0
0
6
Scheme 1 The reactions between chalcone 2a and 1b.
DOI: 10.1055/s-2005-923602; Art ID: W07105ST
© Georg Thieme Verlag Stuttgart · New York

284
D. Dong et al.
LETTER
The reaction between 1b and chalcone 2a was initially in- above results have demonstrated that compound 1b can be
vestigated in the presence of NaOH (Scheme 1). After the used as an ethanethiol equivalent in thia-Michael addition
mixture of 1b (1.0 mmol), chalcone 2a (2.0 mmol) and reactions in EtOH or MeOH under mild basic conditions.
NaOH (0.5 mmol) was stirred in EtOH (99%, 5.0 mL) at
room temperature for six hours, workup, and column
chromatography of the resulting mixture furnished white
crystals in 89% yield (Table 1, entry 1). The product was
Taking the optimized conditions (Table 1, entry 2) a range
of reactions were performed on compounds 1a–e13 with a
variety of a,b-unsaturated carbonyl compounds 2.15 All
the reactions proceeded smoothly under mild basic condi-
characterized as 3-(ethylthio)-1,3-diphenylpropan-1-one
tions to afford the corresponding thia-Michael adducts
(3b), a thia-Michael adduct, on the basis of its elemental
3a–v in very high yields at room temperature (Table 2).
The results obtained demonstrate both the scope and gen-
erality of the novel thia-Michael addition reaction with
respect to various a,b-unsaturated ketones, e.g. chalcone
and its derivatives (Table 2, entries 1–9), aliphatic conju-
gated ketones (Table 2, entries 10–15), and aliphatic con-
jugated esters (Table 2, entries 16–22). Moreover,
analyses and spectral data. It is noteworthy that 3-oxo-N-
o-tolylbutanamide 4 was obtained as a byproduct from the
reaction system in 75% yield; this is easily separable by
silica gel chromatography and can be reused for the pre-
paration of compounds 1. Much to our delight only a very
faint odor of ethanethiol can be perceived during both the
reaction and workup, indicating that the generated thiolate
anions quickly undergo conjugate addition.
compound 4 was obtained as a byproduct in high yield in
all cases.
To optimize the conditions of the thia-Michael addition, a
Our early work revealed that the course of the decompo-
range of reactions between chalcone 2a and 1b (2:1 molar
sition reaction of a-oxo ketene-S,S-acetals was structure
ratio) were carried out under various conditions, and some
dependent.11 Under acidic conditions, for example, 3-
of the results are summarized in Table 1. Apparently, the
(1,3-dithian-2-ylidene)pentane-2,4-dione and 2-(1,3-
amount of NaOH greatly affects the cleavage rate of 1b
and the subsequent conjugate addition to chalcone 2a in
dithian-2-ylidene)-3-oxobutanamide underwent a deacyl-
ation reaction, whereas 2-(1,3-dithian-2-ylidene)-3-oxo-
EtOH (Table 1, entries 1–3). It is observed that the reac-
butanoic acid underwent a decarboxylation reaction. 3-
tion is significantly accelerated when the feed ratio of
Oxo-N-o-tolylbutanamide 4 was obtained in the thia-
NaOH/1b is increased from 1:2 to 1:1. However, the reac-
Michael addition, which suggested that 1a–e might de-
tion rate changes very slightly beyond the ratio of 1:1,
compose in a different manner under basic conditions. In
which indicates the highest reaction rate can be attained
other words, the present results revealed that the reaction
when the reaction proceeds with a 1:1 molar ratio of
conditions had a great effect on the decomposition behav-
NaOH/1b (Table 1, entry 2). Interestingly, the reactions
iors of a-oxo ketene-S,S-acetals. On the basis of the exper-
could proceed in the presence of some weak bases, such
imental results together with our previous studies,9,10,14
a
as K2CO3 and DBU. In these cases, however, prolonged
reaction times were required. The reaction between 1b
and 2a was then examined in various reaction media. The
results reveal that the reaction proceeded smoothly in
MeOH to give 3b in good yield (Table 1, entry 6), but was
unsuccessful in THF or CH2Cl2. Nevertheless, all the
mechanism for the Michael addition reaction of a,b-un-
saturated carbonyl compounds 2 using 1a–e as odorless
thiol equivalents is proposed in Scheme 2. In the presence
of NaOH in EtOH, compound 1 is converted into 2-(di-
ethoxymethylene)-3-oxo-N-o-tolylbutanamide 5 with the
release of a thiolate anion through a nucleophilic vinylic
Table 1 Reactions between Chalcone 2a and 1ba
Entry
Base
Ratiob
1:2
Solvent
EtOH
EtOH
EtOH
EtOH
EtOH
MeOH
THF
Time (min)
360
Yield 3ac (%)
Yield 4c (%)
1
2
3
4
5
6
7
8
NaOH
NaOH
NaOH
K2CO3
DBU
89
94
95
90
89
94
–
75
82
82
78
78
76
–
1:1
50
2:1
40
1:1
600
1:1
700
NaOH
NaOH
NaOH
1:1
50
1:1
600
1:1
CH2Cl2
600
–
–
a Molar ratio 2a/1b, 2:1.
b Molar ratio base/1b.
c Isolated yields.
Synlett 2006, No. 2, 283–287 © Thieme Stuttgart · New York

LETTER
Thia-Michael Addition Reactions
285
Table 2 Reactions between 1 and a,b-Unsaturated Carbonyl Compounds 2
R1
O
O
O
O
SR
R2
O
O
NaOH
+
N
R3
N
+
R2
R3
R1
EtOH
r.t.
H
H
RS
SR
R4
R4
1
4
2
3
Entry
Substrate
1
R
Substrate 2 R1
R2
R3
R4
Time
(min)
Product 3 Yield 3
Yield 4
(%)a
(%)a
1
2
1a
1b
1c
1d
1e
1b
1e
1b
1e
1b
1e
1b
1e
1b
1e
1b
1e
1a
1b
1c
1d
1e
Me
Et
2a
2a
2a
2a
2a
2b
2b
2c
2c
2d
2d
2e
2e
2f
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H
50
50
3a
3b
3c
3d
3e
3f
94
94
93
90
92
92
95
93
95
96
94
90
93
90
89
90
91
90
91
92
89
90
83
82
82
84
81
80
83
85
85
86
85
86
86
82
85
83
84
83
81
83
83
81
H
H
3
n-Bu
Allyl
Bn
Et
H
H
55
4
H
H
60
5
H
H
50
6
H
p-ClPh
p-ClPh
Ph
H
50
7
Bn
Et
H
H
50
3g
3h
3i
8
H
p-ClPh
p-ClPh
Me
H
50
9
Bn
Et
H
Ph
H
55
10
11
12
13
14
15
16
17
18
19
20
21
22
H
Ph
H
60
3j
Bn
Et
H
Ph
Me
H
55
3k
3l
CH3
CH3
H
CH3
CH3
CH3
H
60
Bn
Et
CH3
H
55
3m
3n
3o
3p
3q
3r
3s
–(CH2)3–
–(CH2)3–
H
50
Bn
Et
2f
H
H
55
2g
2g
2h
2h
2h
2h
2h
H
H
OEt
CH3
CH3
H
180
180
240
240
240
270
240
Bn
Me
Et
H
H
OEt
OEt
OEt
OEt
OEt
OEt
H
Ph
Ph
Ph
Ph
Ph
H
H
n-Bu
Allyl
Bn
H
H
3t
H
H
3u
3v
H
H
a Isolated yields.
substitution processes (SNV). Further attack by OH– on 5 situ generated thiolate anions undergo facile conjugate
results in the intermediates 6 and then 7, which undergo addition to a,b-unsaturated carbonyl compounds 2, af-
decarboxylation to afford compound 4 (the precursor to fording the corresponding b-keto sulfides 3 in very high
compounds 1). The in situ generated thiolate anions un- yields. Meanwhile, 3-oxo-N-o-tolylbutanamide 4, the pre-
dergo conjugate addition to 2 to afford the corresponding cursor of compounds 1, can be recovered in the thia-
thia-Michael adducts, b-keto sulfides 3.
Michael addition reactions as a byproduct in high yield.
The mild conditions and high yields, especially in relation
to recent environmental concerns, associated with this
simple procedure, make this novel thia-Michael addition
a facile and convenient protocol for the synthesis of b-
keto sulfides.
In summary, a series of 2-[bis(alkylthio)methylene]-3-
oxo-N-o-tolylbutanamides 1a–e have been investigated as
nonthiolic and odorless substitutes for thiols in thia-
Michael addition reactions. Promoted by NaOH in EtOH
at room temperature cleavage of compounds 1 occurs, in
Synlett 2006, No. 2, 283–287 © Thieme Stuttgart · New York

286
D. Dong et al.
LETTER
(5) Nishide, K.; Ohsugi, S.; Shiraki, H.; Tamakita, H.; Node, M.
Org. Lett. 2001, 3, 3121.
(6) (a) Bertini, V.; Lucchesini, F.; Pocci, M.; De Munno, A.
Tetrahedron Lett. 1998, 39, 9263. (b) Bertini, V.;
O
O
O
O
NaOH
EtOH
RS–
+
N
N
H
H
EtO
OEt
RS
SR
Lucchesini, F.; Pocci, M.; De Munno, A. J. Org. Chem.
2000, 65, 4839. (c) Bertini, V.; Pocci, M.; Lucchesini, F.;
Alfei, S.; De Munno, A. Synlett 2003, 864.
5
1
OH–
– EtO–
R2
O
O
O
O
(7) Iimura, S.; Manabe, K.; Kobayashi, S. Org. Lett. 2003, 5,
101.
(8) Ranu, B. C.; Mandal, T. Synlett 2004, 1239.
R1
R3
N
H
R4
OEt
(9) (a) Liu, Q.; Che, G.; Yu, H.; Liu, Y.; Zhang, J.; Zhang, Q.;
Dong, D. J. Org. Chem. 2003, 68, 9148. (b) Yu, H.; Liu, Q.;
Yin, Y.; Fang, Q.; Zhang, J.; Dong, D. Synlett 2004, 999.
(c) Dong, D.; Ouyang, Y.; Yu, H.; Liu, Q.; Wang, M.; Zhu,
J. J. Org. Chem. 2005, 70, 4535. (d) Liu, J.; Liu, Q.; Yu, H.;
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(10) Yu, H.; Dong, D.; Ouyang, Y.; Liu, Q.; Wang, Y. Lett. Org.
Chem. 2005, 2, 755.
2
6
OH–
O
SR
O
O
O
O
O
– CO2
R3
R1
N
R2
N
H
R4
H
O–
7
4
3
(11) (a) Dieter, R. K. Tetrahedron 1986, 42, 3029. (b) Junjappa,
H.; Ila, H.; Asokan, C. V. Tetrahedron 1990, 46, 5423.
(c) Kolb, M. Synthesis 1990, 171.
Scheme 2 A proposed mechanism for the reactions between 1 and
a,b-unsaturated carbonyl compounds 2.
(12) (a) Choi, E. B.; Youn, I. K.; Pak, C. S. Synthesis 1988, 792.
(b) Pak, C. S.; Choi, E. B. Synthesis 1992, 1291.
Acknowledgment
(13) Selected data for compounds 1: 2-[Bis(methylthio)meth-
ylene]-3-oxo-N-o-tolylbutanamide (1a) Yellow solid; mp
102–104 °C. IR (KBr, neat): 3361, 2980, 1647, 1523, 1453
cm–1. 1H NMR (500 MHz, CDCl3): d = 2.31 (s, 3 H), 2.48 (s,
6 H), 2.52 (s, 3 H), 7.06–7.09 (m, 1 H), 7.18–7.25 (m, 2 H),
8.05 (d, J = 8.0 Hz, 1 H), 8.21 (br, 1 H). Anal. Calcd for
C14H17NO2S2: C, 56.92; H, 5.80; N, 4.74. Found: C, 56.84;
H, 5.77; N, 4.76. 2-[Bis(butylthio)methylene]-3-oxo-N-o-
tolylbutanamide (1c) Yellow solid; mp 48–50 °C. IR (KBr,
neat): 3345, 2957, 1650, 1526, 1454 cm–1. 1H NMR (500
MHz, CDCl3): d = 0.90–0.93 (m, 6 H), 1.39–1.46 (m, 4 H),
1.60–1.66 (m, 4 H), 2.31 (s, 3 H), 2.53 (s, 3 H), 2.92–2.95
(m, 4 H), 7.06–7.09 (m, 1 H), 7.18–7.24 (m, 2 H), 8.02 (d,
J = 8.0 Hz, 1 H), 8.23 (br, 1 H). Anal. Calcd for C20H29NO2S2:
C, 63.28; H, 7.70; N, 3.69. Found: C, 63.36; H, 7.67; N, 3.64.
(14) Wang, M.; Xu, X.; Sun, S.; Liu, Q. Synth. Commun. 2004,
34, 287.
(15) Selected data for compounds 3: 3-(Methylthio)-1,3-di-
phenylpropan-1-one (3a) White crystals, mp 55–57 °C. IR
(KBr, neat): 3059, 2912, 1685, 1595, 1494, 1225 cm–1. 1H
NMR (500 MHz, CDCl3): d = 1.93 (s, 3 H), 3.55 (m, 2 H),
4.47 (m, 1 H), 7.21–7.24 (m, 1 H), 7.30–7.33 (m, 2 H), 7.40–
7.46 (m, 4 H), 7.51–7.57 (m, 1 H), 7.92 (d, J = 8.0 Hz, 2 H).
Anal. Calcd for C16H16OS: C, 74.96; H, 6.29. Found: C,
74.85; H, 6.33. Ethyl 3-(methylthio)-3-phenylpropanoate
(3r) Colorless liquid. IR (KBr, neat): 3028, 2980, 1736,
1601, 1490, 1215 cm–1. 1H NMR (500 MHz, CDCl3): d =
1.14–1.16 (m, 3 H), 1.90 (s, 3 H), 2.82–2.93 (m, 2 H), 4.03–
4.09 (m, 2 H), 4.18–4.21 (m, 1 H), 7.21–7.24 (m, 1 H), 7.25–
7.33 (m, 4 H). Anal. Calcd for C12H16O2S: C, 64.25, H, 7.19.
Found: C, 64.34, H 7.13. Ethyl 3-(ethylthio)-3-phenyl-
propanoate (3s) Colorless liquid. IR (KBr, neat): 3061,
2976, 1732, 1601, 1492, 1213 cm–1. 1H NMR (500 MHz,
CDCl3): d = 1.13–1.17 (m, 6 H), 2.30–2.36 (m, 2 H), 2.81–
2.90 (m, 2 H), 4.04–4.30 (m, 2 H), 4.28–4.32 (m, 1 H), 7.21–
7.24 (m, 1 H), 7.28–7.35 (m, 4 H). 13C NMR (125 MHz,
CDCl3): d = 13.8, 14.1, 24.9, 41.3, 44.7, 60.4, 127.1, 127.4
(2 C), 128.2 (2 C), 141.2, 170.5. Anal. Calcd for C13H18O2S:
C, 65.51; H, 7.61. Found: C, 65.59; H, 7.57. Ethyl 3-(butyl-
thio)-3-phenylpropanoate (3t) Colorless liquid. IR (KBr,
neat): 3061, 2958, 1737, 1602, 1489, 1214 cm–1. 1H NMR
(500 MHz, CDCl3): d = 0.84 (t, 3 H), 1.15 (t, 3 H), 1.27–1.36
(m, 2 H), 1.44–1.51 (m, 2 H), 2.27–2.37 (m, 2 H), 2.81–2.91
(m, 2 H), 4.02–4.09 (m, 2 H), 4.25–4.28 (m, 1 H), 7.21–7.24
Financial support of this research was provided by the NNSFC
(20572013), the Key Project of the Ministry of Education of China
(105061), and the Key Grant Project of the Ministry of Education of
China (10412).
References and Notes
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Synlett 2006, No. 2, 283–287 © Thieme Stuttgart · New York

LETTER
(m, 1 H), 7.29–7.35 (m, 4 H). Anal. Calcd for C15H22O2S: C,
Thia-Michael Addition Reactions
287
thio)-3-phenylpropanoate (3v) Colorless liquid. IR (KBr,
neat): 3061, 2980, 1735, 1601, 1584, 1493, 1370 cm–1. 1H
NMR (500 MHz, CDCl3): d = 1.10–1.14 (m, 3 H), 2.81–2.88
(m, 2 H), 3.46 (d, J = 13 Hz, 1 H), 3.56 (d, J = 13 Hz, 1 H),
4.00–4.06 (m, 2 H), 4.15–4.18 (m, 1 H), 7.21–7.35 (m, 10
H). 13C NMR (125 MHz, CDCl3): d = 13.8, 35.4, 41.2, 44.7,
60.4, 126.8, 127.2, 127.7 (2 C), 128.2 (2 C), 128.3 (2 C),
128.7 (2 C), 137.5, 140.8, 170.3. Anal. Calcd for C18H20O2S:
C, 71.96; H, 6.71. Found: C, 71.87; H, 6.75.
67.63; H, 8.32. Found: C, 67.55; H, 8.34. Ethyl 3-
(allylthio)-3-phenylpropanoate (3u): Colorless liquid. IR
(KBr, neat): 3079, 2958, 1737, 1599, 1454, 1249 cm–1. 1H
NMR (500 MHz, CDCl3): d = 1.14–1.17 (m, 3 H), 2.81–2.93
(m, 3 H), 3.00–3.03 (m, 1 H), 4.04–4.08 (m, 2 H), 4.25–4.28
(m, 1 H), 5.04–5.11 (m, 2 H), 5.72–5.80 (m, 1 H), 7.22–7.25
(m, 1 H), 7.30–7.35 (m, 4 H). Anal. Calcd for C14H18O2S: C,
67.16; H, 7.25. Found: C, 67.25; H, 7.19. Ethyl 3-(benzyl-
Synlett 2006, No. 2, 283–287 © Thieme Stuttgart · New York