A clean, facile and practical synthesis of α-oxoketene S,S-acetals in water

Article abstract of DOI:10.1002/adsc.200505331

A clean, facile and practical synthesis of α-oxoketene S,S-acetals in water has been developed. Catalyzed by tetrabutylammonium bromide (TBAB) at room temperature in water, a range of β-dicarbonyl compounds have been converted to the corresponding α-oxoke

Full text of DOI:10.1002/adsc.200505331

FULL PAPERS
DOI: 10.1002/adsc.200505331
A Clean, Facile and Practical Synthesis of a-Oxoketene
S,S-Acetals in Water
Yan Ouyang, Dewen Dong,* Haifeng Yu, Yongjiu Liang, Qun Liu*
Department of Chemistry, Northeast Normal University, Changchun 130024, Peopleꢀs Republic of China
Fax: (þ86)-431-509-8635, e-mail: dongdw663@nenu.edu.cn
Received: August 28, 2005; Accepted: November 14, 2005
Abstract: A clean, facile and practical synthesis of a- lyst in the aqueous phase can be recycled after the
oxoketene S,S-acetals in water has been developed. separation of organic products.
Catalyzed by tetrabutylammonium bromide (TBAB)
at room temperature in water, a range of b-dicarbonyl Keywords: carbon disulfide; b-dicarbonyl compounds;
compounds have been converted to the corresponding a-oxoketene S,S-acetals; tetrabutylammonium bro-
a-oxoketene S,S-acetals in very high yields. The cata- mide; water
Introduction
benefit from the fact that water is an easily available,
cheap, safe and environmentally benign solvent.[11] Lat-
Over the past decades, the utility of a-oxoketene S,S- er on, extensive work has revealed that a variety of or-
acetals as versatile intermediates in organic synthesis ganic reactions including the Mukaiyama aldol reaction,
has been recognized.[1] As three-carbon 1,3-bielectro- allylation reactions, Diels–Alder reaction, Michael re-
philic synthons, a-oxoketene S,S-acetals have been ex- actions, Mannich-type reactions and even dehydration
tensively investigated and widely applied in the syn- reactions can be realized in the presence of various cat-
thesis of substituted and fused aromatic and heterocy- alysts such as inverse phase-transfer catalysts and sur-
clic structural frameworks by reacting them with nucle- factant-type Lewis or Brønsted acids in water.[12,13]
ophiles such as Grignard reagents,[2] Reformatsky re-
Our laboratory has been engaging in the synthesis and
agents,[3] organolithium reagents[4] and organocuprate application of a-oxoketene S,S-acetals for a decade.[14]
reagents.[5] Indeed, the first synthesis of an a-oxoke- Recently, we developed a novel thioacetalization reac-
tene S,S-acetal was reported in 1910 by Kelber and tion in water using an a-oxoketene S,S-acetal, 3-(1,3-di-
co-workers.[6] This compound was prepared by alkyla- thian-2-ylidene)pentane-2,4-dione, as a 1,3-propanedi-
tion of b-oxodithioic acid which was obtained in poor thiol equivalent and p-dodecylbenzenesulfonic acid
yield by reaction of an aryl ketone with CS2 and KOH (DBSA, a surfactant-type Brønsted acid) as the cata-
at 1008C followed by neutralization with sulfuric lyst.[15] As part of our continuing interest in organic reac-
acid. In the early 1960s, Thuillier and Vialle successful- tions in water, the present work aims at the synthesis of
ly prepared a-oxoketene S,S-acetals directly from ke- a-oxoketene S,S-acetals in water.
tones in good yields by using sodium tert-amylate as
the base and two equivalents of an alkyl halide.[7] Sub-
sequent workers devoted their efforts towards improv- Results and Discussion
ing the synthetic methodology and achieved mild reac-
tion conditions, high yields and wide generality to wide Acyl(alkoxycarbonyl)ketene S,S-acetals are known to
substrates for the synthesis of a-oxoketene S,S-ace- be prepared in poor yields from ketones using a strong
tals.[8] However, there are only a few reports so far on base such as sodium tert-amylate, sodium hydride and
the synthesis of a-oxoketene S,S-acetals in aqueous lithium 4-methyl-2,3-di-tert-butylphenoxide in the pres-
media,[9] and none in water.
ence of carbon disulfide and subsequent S-alkylation
The use of water as a solvent in organic chemistry was with the appropriate alkyl halide.[1a] Choi and co-work-
rediscovered in the 1980s in Breslowꢀs work, which ers improved the method by choosing K2CO3 as the
showed that a hydrophobic effect can strongly enhance base and N,N-dimethylformamide as the reaction me-
the rates of some organic reactions.[10] Organic reactions dium and obtained acyl(alkoxycarbonyl)ketene S,S-ace-
in water without the use of any organic solvent can also tals from b-oxo esters in very high yields, and applied
206
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Synthesis of a-Oxoketene S,S-Acetals in Water
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Table 1. Preparation of 3aa from acetyl acetone 1a in water.
Entry
Cat.
Amount[a] [mmol]
H2O [mL]
K2CO3 [mmol]
1a [mmol]
Time[b] [h]
24
Yield[c] [%]
1
2
3
4
5
6
7
8
9
SDBS
5.0
5.0
2.5
1.0
0.5
0.0
15
15
15
15
15
15
0
25
25
25
25
25
25
25
25
25
10
10
10
10
10
10
10
10
10
0
97
96
96
82
0
96
95
91
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB[d]
TBAB[e]
TBAB[f]
6.0
6.0
6.0
7.0
24
2nd use
3rd use
4th use
6.0
6.0
7.0
0
0
[a]
Amount of catalyst
[b]
[c]
[d]
[e]
[f]
The reaction time was recorded after the addition of bromoethane
Isolated yields of 3aa obtained by filtration.
Aqueous filtrate from entry 4.
Aqueous filtrate from entry 7.
Aqueous filtrate from entry 8.
this protocol in the synthesis of acyl(arylcarbamoyl)ke- has been filtered and washed with water, which provides
tene S,S-acetals from b-oxo amides.[16]
a very simple separation process. In contrast to the
In the present work, the reaction of 3-oxo-N-o-tolyl- above results, the reaction without TBAB cannot yield
butanamide 1a (1.0 equiv.) with carbon disulfide the desired a-oxoketene S,S-acetal product (entry 6).
(1.2 equivs.) in the presence of K2CO3 (2.5 equivs.) and The results indicate that the catalyst TBAB plays a
sodium p-dodecylbenzenesulfonate (SDBS, 0.5 equivs.) key role in the reactions in water.
in water and subsequent S-alkylation with 1,2-dibromo-
ethane 2a (1equiv.) was first attempted (Table 1, entry
Obviously, the resulting aqueous filtrate after the sep-
aration of organic products still contains the catalyst
1). Unfortunately, no desired a-oxoketene S,S-acetal TBAB, which prompted us to investigate recycling of
product was even detected in the reaction mixture. the catalyst. Thus, the reaction of 1a with carbon disul-
Then the reaction was performed on 1a (1.0 equiv.) fide (1.2 equivs.) and K2CO3 (2.0 equivs.) was carried
with carbon disulfide (1.2 equivs.) in the presence of out using the aqueous filtrate containing TBAB as reac-
K2CO3 (2.5 equivs.) and tetrabutylammonium bromide tion medium following in a similar fashion as described
(TBAB, 0.5 equivs.) in water and subsequent S-alkyla- above. After the reaction was completed as indicated by
tion with 2a (1equiv.). To our delight, the reaction pro-
TLC, separation of the resulting mixture by filtration
ceeded smoothly at room temperature to afford 2-(1,3- furnished 3aa in 96% yield (entry 7). Further studies re-
dithiolan-2-ylidene)-3-oxo-N-o-tolylbutanamide 3aa in veal that TBAB can attain very high catalytic activity
97% yield (entry 2). To optimize the reaction conditions, even when it was used for the four times (entry 9). The
several reactions were carried out in which the feed mo- results demonstrate that the catalyst can be recycled,
lar ratio of TBAB to 1a was changed from 1/2 to 1/100, at least for several times, by reuse of the aqueous phase
and the molar ratio among other reactants was kept con- after the separation of organic products. Therefore, we
stant. Some of the results are summarized in Table 1. It is present a clean, facile and practical protocol for the syn-
noted that there is nearly no change in the yields and thesis of a-oxo ketene S,S-acetals in water.
rates of the reactions when decreasing the addition of
To test the general applicability of this protocol, a ser-
DBAB from a stoichiometric amount to a catalytic ies of b-dicarbonyl compounds 1b–f were selected for
amount of TBAB/1a (entries 2–4). Too low a feed molar the investigation. Subjected to the optimized reaction
ratio of TBAB/1a, 5 mol % for example, makes the reac- conditions as described in Table 1entry 4, compounds
tion a little sluggish and with accompanying small 1b–f were converted into the corresponding a-oxoke-
amounts of unreacted starting materials (entry 5). In tene S,S-acetals 3 in excellent yields. Some of the results
the cases of entries 2–4, the product is solid and can de- are summarized in Table 2.
posit from the reaction system once formed. The pure
On the basis of these results, an interfacial mechanism
product is obtained in excellent yield after the solid for the reaction 1 with carbon disulfide and alkyl halide 2
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Yan Ouyang et al.
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Table 2. Preparation of a-oxoketene S,S-acetals 3 from b-dicarbonyl compounds 1 in water.
Entry
Substrate
Substrate
Time[a] [h]
Product 3
Yield[c] [%]
Ref.
1
R1
R2
2
R
R
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1a
1a
1a
1b
1b
1b
1c
1c
1c
1d
1d
1d
1e
1e
1e
1f
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
2-CH3C6H4NH
2-CH3C6H4NH
2-CH3C6H4NH
2-CH3OC6H4NH
2-CH3OC6H4NH
2-CH3OC6H4NH
4-ClC6H4NH
4-ClC6H4NH
4-ClC6H4NH
CH3
CH3
CH3
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
2a
2b
2c
2a
2b
2c
2a
2b
2c
2a
2b
2c
2a
2b
2c
2a
2b
2c
-(CH2)2-
-(CH2)3-
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
6.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
3aa
3ab
3ac
3ba
3bb
3bc
3ca
3cb
3cc
3da
3db
3dc
3ea
3eb
3ec
3fa[b]4f]
3fb
98
96
97
97
98
99
93
95
96
97
92
95
94
95
98
91[1
90
92
PhCH2
-(CH2)2-
-(CH2)3-
PhCH2 PhCH2
PhCH2
-(CH2)2-
-(CH2)3-
PhCH2
PhCH2
-(CH2)2-
-(CH2)3-
[14b, g]
[14b, g]
[14e]
[16a]
[16a]
PhCH2
PhCH2
-(CH2)2-
-(CH2)3-
PhCH2
PhCH2
[14e]
OC2H5
OC2H5
OC2H5
-(CH2)2-
-(CH2)3-
1f
1f
[14g]
[14e]
PhCH2
PhCH2
3fc
[a]
The reaction time was recorded after the addition of alkyl halide.
Liquid product, separation was carried out by extraction with diethyl ether followed by washing with water.
Isolated yields for solid products 3, separation was carried out by filtration and washing with water.
[b]
[c]
is assumed as shown in Scheme 1. The reaction starts
from the deprotonation of b-dicarbonyl compound 1
to afford the enolates 4 and 5 in the presence of
K2CO3 and TBAB. In the aqueous phase near the inter-
face, the nucleophilic attack of the enolates 4 and 5 on
carbon disulfide occurs to form thiolate 6. As a tautomer
of 6, unsaturated monothiolate anion 7 undergoes the S-
alkylation with alkyl bromide, finally yielding the corre-
sponding a-oxoketene S,S-acetal 3.
Experimental Section
Typical Procedure for the Preparation of a-Oxoketene
S,S-Acetals 3 (3aa as Example)
To a solution of 3-oxo-N-o-tolylbutanamide 1a (10 mmol),
K2CO3 (25 mmol) and TBAB (1.0 mmol) in water (15 mL) at
room temperature was added CS2 (12 mmol) under stirring.
After the reaction mixture was stirred at room temperature
for 1.0 h, 1,2-dibromoethane (10 mmol) was added dropwise
within 15 min. Then the resulting mixture was stirred for 6 h
at room temperature. The precipitated solid was collected by
filtration, washed with water (3Â25 mL), and dried under vacu-
um to afford the product 3aa as a yellowish solid; yield: 98%.
All the compounds 3 listed in Table 2 were prepared follow-
ing the same procedure. As an exception, the separation of 3fa
was carried out by extraction with diethyl ether followed by
washing with water.
Conclusion
In summary, a clean, facile and practical synthesis of a-
oxoketene S,S-acetals has been developed based on the
reaction of b-dicarbonyl compounds with carbon disul-
fide and alkyl bromide catalyzed by tetrabutylammoni-
um bromide in the presence of potassium carbonate in
water. The simple procedure, mild conditions, easy sep-
aration, high yields, and especially the relation to the
current environmental concerns, make this protocol
most attractive for academic research and practical ap-
plications.
Physical Data of Compounds Isolated
Products 3da–3fc are known compounds.
3aa: yellowish solid, mp 140–1428C; H NMR (300 MHz,
CDCl3): d¼2.34 (s, 3H), 2.46 (s, 3H), 3.38 (m, 2H), 3.44 (m,
1
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Synthesis of a-Oxoketene S,S-Acetals in Water
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Scheme 1. A proposed mechanism for the reaction of 1 with CS2 and alkyl bromide in the presence of TBAB and K2CO3 in
water.
2H), 7.11 (m, 1H), 7.22 (m, 2H), 7.93 (m, 1H), 8.10 (s, 1H); 13
C
d¼29.7, 33.3, 41.5, 55.7, 110.1, 120.1, 120.8, 121.0, 124.3,
124.6, 127.2, 128.7, 129.1, 136.4, 142.6, 147.7, 148.4, 162.2,
197.9, 204.6; IR(KBr, neat): n¼3409, 1651, 152, 1433, 1251,
752 cmꢀ1; anal. calcd. for C26H25NO2S2: C 67.36, H 5.44, N
3.02; found: C 67.26, H 5.45, N, 3.04.
NMR (75 MHz, CDCl3): d¼18.1, 28.8, 36.7, 38.4, 122.8, 123.8,
125.4, 126.8, 129.3, 130.6, 135.1, 165.1, 170.1, 193.3; IR (KBr,
neat): n¼3442, 3284, 1647, 1625, 1456, 1306, 1219, 753 cmꢀ1
;
anal. calcd. for C14H15NO2S2: C 57.31, H 5.15, N 4.77; found:
1
C 57.40, H 5.11, N 4.75; MS: m/e¼293 (Mþ, 187).
3ca: yellowish solid, mp 184–1868C; H NMR (300 MHz,
1
CDCl3): d¼2.40 (s, 3H), 3.33–3.45(m, 4H), 7.33 (d, J¼
7.8 Hz, 2H), 7.65 (d, J¼7.8 Hz, 2H), 8.64 (s, 1H); 13C NMR
(75 MHz, CDCl3): d¼28.7, 36.7, 38.5, 121.3, 123.5, 129.1,
129.6, 136.5, 162.2, 171.1, 193.3; IR (KBr, neat): n¼3281,
1625, 1453, 1247, 831 cmꢀ1; anal. calcd. for C13H12ClNO2S2: C
49.75, H 3.85, N 4.46; found: C 49.64, H 3.81, N 4.42.
3ab: yellowish solid, mp 122–1248C; H NMR (300 MHz,
CDCl3): d¼2.25 (t, J¼6.0 Hz, 2H), 2.32 (s, 3H), 2.43 (s, 3H),
2.99 (t, J¼6.0 Hz, 4H), 7.11 (m, 1H), 7.20–7.25 (m, 2H), 7.90
(s, 1H), 7.97 (d, 1H); 13C NMR (75 MHz, CDCl3): d¼18.0,
24.0, 28.2, 29.0, 29.7, 122.9, 125.4, 126.7, 129.3, 130.6, 132.3,
135.5, 164.2, 164.4, 194.3; IR (KBr, neat): n¼3457, 3348,
1646, 1516, 1454, 1285, 834 cm ꢀ1; anal. calcd. for C15H17NO2S2:
C 58.60, H 5.57, N 4.56; found: C 58.51, H 5.61, N, 4.55; MS:
m/e¼307 (Mþ, 214).
1
3cb: yellowish solid, mp 194–1968C; H NMR (300 MHz,
CDCl3): d¼2.19 (m, 2H), 2.38 (s, 3H), 2.90–3.01 (m, 4H),
7.20 (d, J¼7.8 Hz, 2H), 7.67 (d, J¼7.8 Hz, 2H), 8.50 (s, 1H);
13C NMR (75 MHz, CDCl3): d¼24.0, 29.0, 29.2, 29.8, 121.1,
129.0, 129.5, 132.2, 136.6, 164.2, 165.6, 194.1; IR (KBr, neat):
3ac: yellowish solid, mp 70–728C; 1H NMR (300 MHz,
CDCl3): d¼2.18 (s, 3H), 2.41 (s, 3H), 4.15 (m, 4H), 6.92–7.45
(m, 14H), 7.76 (s, 1H); 13C NMR (75 MHz, CDCl3): d¼17.8,
30.1, 39.4, 41.5, 123.0, 125.5, 126,6 127.7, 128.8, 129.0, 129.3,
129.6, 130.4, 131.4, 132.8, 134.9, 135.1, 136.7, 143.8, 146.0,
162.1, 198.7; IR (KBr, neat): n¼3370, 3026, 1668, 1515, 1453,
1203, 866 cmꢀ1; anal. calcd. for C26H25NO2S2: C 69.77, H 5.63,
N 3.13, Found: C 69.69; H 5.61, N 3.15.
n¼3430, 1644, 1397, 1249, 829 cmꢀ1
; anal. calcd. for
C14H14ClNO2S2: C 51.29, H 4.30, N 4.27; found: C 51.39, H
4.31, N, 4.22.
1
3cc: yellowish solid, mp 144–1468C; H NMR (300 MHz,
CDCl3): d¼2.15 (s, 3H), 4.14 (m, 4H), 7.15–7.30 (m, 14H),
7.25 (s, 1H); 13C NMR (75 MHz, CDCl3): d¼30.0, 39.2, 41.5,
121.3, 128.1, 128.5, 128.8, 129.4, 130.7, 135.8, 136.8, 143.6,
146.2, 149.3, 162.2, 198.0; IR (KBr, neat): n¼3321, 1665,
1315, 1246, 826 cmꢀ1; anal. calcd. for C25H22ClNO2S2: C
64.16, H 4.74, N 2.99; found: C 64.24, H 4.69, N, 3.03.
1
3ba: yellowish solid, mp 112–1148C; H NMR (300 MHz,
CDCl3): d¼2.32 (s, 3H), 3.35 (m, 2H), 3.45 (m, 2H), 3.88 (s,
3H), 6.91(d, J¼7.8 Hz, 1H), 7.03 (m, 1H), 7.09 (m, 1H), 8.25
(s, 1H), 8.47 (d, J¼7.8 Hz, 1H); 13C NMR (75 MHz, CDCl3):
d¼28.3, 36.5, 38.5, 55.8, 110.1, 120.0, 121.2, 124.3, 127.3,
148.3, 165.2, 169.6, 191.8, 192.1; IR (KBr, neat): n¼3410,
1652, 1521, 1461, 1434, 1285, 1251, 753 cmꢀ1; anal. calcd. for
C14H15NO2S2: C 54.35, H 4.89, N 4.53; found: C 54.24, H 4.93,
N 4.54.
Acknowledgements
Financial supports of this research by the NNSFC (20272008
and 20572013) and the Key Project of the Ministry of Education
of China (105061) are greatly acknowledged
1
3bb: yellowish solid, mp 162–1648C; H NMR (300 MHz,
CDCl3): d¼2.23 (m, 2H), 2.34 (s, 3H), 2.96 (m, 4H), 3.88 (s,
3H), 6.89 (d, J¼7.8 Hz, 1H), 6.99 (m, 1H), 7.04 (m, 1H), 8.20
(s, 1H), 8.47 (d, J¼7.8 Hz, 1H); 13C NMR (75 MHz, CDCl3):
d¼23.9, 28.8, 28.9, 29.3, 55.1, 110.1, 119.9, 121.1, 124.3, 127.4,
132.7, 148.2, 164.3, 164.7, 197.8; IR (KBr, neat): n¼3282,
1665, 1637, 1600, 1528, 1462, 1258, 1230, 756 cmꢀ1; anal. calcd.
for C15H17NO2S2: C 55.70, H 5.30, N 4.33, found: C 55.62, H
5.34, N, 4.31.
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J¼7.8 Hz, 1H), 6.87–7.15 (m, 2H), 7.16–7.27 (m, 10H), 8.30
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Yan Ouyang et al.
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