A highly efficient sulfur-catalyzed oxidative carbonylation of primary amines and β-amino alcohols

Article abstract of DOI:10.1055/s-2006-926254

A highly efficient sulfur-catalyzed oxidative carbonylation of aliphatic amines and aliphatic β-amino alcohols to ureas and 2-oxazolidinones, respectively, was developed. Sodium nitrite was involved in the reoxidation of hydrogen sulfide to sulfur in the catalytic oxidative carbonylation cycle. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-926254

LETTER
1161
A Highly Efficient Sulfur-Catalyzed Oxidative Carbonylation of Primary
Amines and b-Amino Alcohols
S
X
ulfur-CatalyzedO
i
xidativ
n
e
C
arbonyla
g
tionof
P
rim
a
A
mineso Peng, Fuwei Li, Chungu Xia*
State Key Laboratory of Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
and Graduate School of the Chinese Academy of Sciences, Lanzhou, 730000 Gansu, P. R. of China
Fax +86(931)8277088; E-mail: cgxia@lzb.ac.cn
Received 6 November 2005
a metal-free system such as the one reported by Sonoda,9
Abstract: A highly efficient sulfur-catalyzed oxidative carbonyl-
in which case selenium was used as an efficient catalyst.
ation of aliphatic amines and aliphatic b-amino alcohols to ureas
10
and 2-oxazolidinones, respectively, was developed. Sodium nitrite In 1961, Franz reported an oxidative carbonylation pro-
was involved in the reoxidation of hydrogen sulfide to sulfur in the
catalytic oxidative carbonylation cycle.
cess of amines to ureas. In their process, a stoichiometric
amount of sulfur was used and H S was produced as a by-
2
Key words: sulfur, oxidative carbonylation, amine, b-aminoalco- product. One of the drawbacks was that H S causes
2
hol, catalysis
serious environmental pollution and equipment corrosion.
In 2003, Hu reported a TEMPO-Br /NaNO system to
2
2
11
catalyze the oxidation of alcohols, in which NaNO was
2
Ureas and 2-oxazolidinones are very important N-con- used to oxidize HBr in situ to Br and then thus established
2
taining carbonyl compounds that possess wide appli- an effective oxidative system with a catalytic amount of
cations as intermediates for fine chemicals, Br . We envisaged that if H S, produced in the oxidative
2
2
1
pharmaceuticals, cosmetics and pesticides. They have carbonylation process, could be re-oxidized to regenerate
also been used as plant growth regulators, agrochemicals, sulfur by an appropriate oxidant; a catalytic oxidative
tranquillizing and anticonvulsant agents. Furthermore, carbonylation process could be established. In this paper,
optically active 2-oxazolidinones have been used as chiral we wish to report a highly efficient catalytic system for
2
auxiliaries in asymmetric synthesis.
the oxidative carbonylation of amines and b-amino alco-
hols to ureas and 2-oxazolidinones, respectively, in the
presence of carbon monoxide (Equation 1 and Equation 2,
respectively), wherein a catalytic amount of sulfur was
The classical syntheses of ureas and 2-oxazolidinones
have been based on the phosgenation of the amino com-
pounds with toxic phosgene or its derivatives, which may
cause serious environmental and health problems. In re-
cent years, alternative routes have been developed that
involved the direct insertion of CO or CO into amino
compounds. Most of these processes required the pres-
ence of a stoichiometric amount of a dehydrating agent or
excess base to neutralize the acidic by-products produced
from amines and carbon dioxide. On the other hand, the
3
used as the catalyst and NaNO as the oxidant.
2
O
2
S/NaNO2
2
RNH2
+
CO
–
H2O
RHN NHR
4
Equation 1
5
catalytic efficiencies were low for processes using catalyt-
ic amount of promoters. For example, N,N¢-diphenylurea
was obtained in 27% yield from the reaction between
O
R2
R1
S/NaNO2
– H2O
HN
R1
O
+
CO
H2N
OH
R2
aniline and CO catalyzed by CsOH/ionic liquid
2
5
(BMImCl). From the standpoint of atom economy, the Equation 2
oxidative carbonylation methodology, which employs
amino compounds, CO, and oxygen as starting materials
The oxidative carbonylation process using n-butylamine
towards the synthesis of 1,3-dibutylurea was investigated.
Firstly, oxidative carbonylation of n-butylamine (20
mmol) was carried out in methanol at 120 °C under 40
and H O as by-product, should become very attractive. In
2
6
7
recent years, many transition metals including Rh, Ru
8
and especially Pd have been reported to catalyze the oxi-
dative carbonylation process. However, such processes
are very expensive in view of the escalating cost of the
metals used. Therefore, it is highly desirable to develop an
oxidative carbonylation of amino compounds to ureas by
atm pressure of CO in the presence of NaNO (2.5 mmol)
2
and sulfur (1 mmol). n-Butylamine (66%) was converted
into 1,3-dibutylurea (65%) and N-butylformamide (35%,
Table 1, entry 1) after 10 hours. Up to 92% conversion
and >99% selectivity for urea formation was obtained
when the amount of NaNO was increased (5 mmol) in the
2
presence of sulfur (1 mmol, Table 1, entry 2). Further
SYNLETT 2006, No. 8, pp 1161–1164
Advanced online publication: 10.03.2006
DOI: 10.1055/s-2006-926254; Art ID: W38505ST
1
5.
0
5.
2
0
0
6
increasing the amount of NaNO to 10 mmol resulted in
2
the quantitative conversion of n-butylamine and >99%
©
Georg Thieme Verlag Stuttgart · New York

1
162
X. Peng et al.
LETTER
selectivity for 1,3-dibutylurea (Table 1, entry 3). Hence, stoichiometric amount of sulfur without NaNO , the reac-
2
the conversion efficiency of n-butylamine as well as the tion proceeded with 100% conversion and >99% selectiv-
reaction selectivity for 1,3-dibutylurea increased with in- ity (Table 1, entry 5), together with the formation of a
creasing amount of NaNO . Therefore, NaNO appeared stoichiometric amount of H S. Therefore, a highly effi-
2
2
2
to be the oxidant in the S/NaNO catalytic system for ox- cient S/NaNO catalytic system for the oxidative carbon-
2
2
idative carbonylation of n-butylamine. Furthermore, no ylation of amino compounds to synthesize ureas was
H S could be detected (by GC) and some regenerated sul- found.
2
fur could be found at the bottom of the autoclave after the
reaction. On the other hand, when the oxidative carbonyl-
ation were carried out under comparable conditions in the
The oxidative carbonylation reaction, carried out under
the optimized conditions found for n-butylamine, was ex-
tended to other primary aliphatic amines and the results
absence of NaNO (Table 1, entry 4), only 15% conver-
12
2
are summarized (Table 1, entries 6–10). The sulfur-cat-
sion of n-butylamine was obtained. In the presence of a
alyst oxidative process showed excellent catalytic activity
a
Table 1 Oxidative Carbonylation of Amines and β-Aminoalcohols Catalyzed by S/NaNO2
Entry
Substrate
n-BuNH2
n-BuNH2
n-BuNH2
n-BuNH2
n-BuNH2
n-PrNH2
t-BuNH2
Product
Catalyst
Oxidant
NaNO2
NaNO2
NaNO2
–
Conversion (%)
Selectivity (%)
1b
2c
3
(n-BuNH) CO
S
S
S
S
S
S
S
S
66
92
65
>99
>99
72
2
(n-BuNH) CO
2
(n-BuNH) CO
100
15
2
4
(n-BuNH) CO
2
5d
6
(n-BuNH) CO
–
100
98
>99
>99
>99
21
2
(n-PrNH) CO
NaNO2
NaNO2
NaNO2
2
7
(t-BuNH) CO
97
2
8
35
NH2
NH 2CO
9
NH2
NH
S
S
S
S
NaNO2
NaNO2
NaNO2
NaNO2
92
98
–
>99
91
2CO
1
1
1
0
1
2
NH2
NH 2CO
NH2
NH
–
2CO
H N
2
OH
OH
O
O
98
>99
HN
HN
O
O
1
1
1
a
3e
4e
5e
2
H N
S
S
S
NaNO2
NaNO2
NaNO2
97
100
100
>99
>99
>99
2
H N
OH
OH
O
HN
O
2
H N
O
HN
O
Reaction conditions: sulfur (1 mmol), amine or ethanolamine (20 mmol), NaNO (10 mmol), MeOH (6 mL), CO (40 atm), 120 °C, 10 h. Con-
2
versions and selectivities are based on GC analysis.
b
NaNO used = 2.5 mmol.
2
c
NaNO used = 5.0 mmol.
2
d
Sulfur used = 10.0 mmol.
Racemic amino alcohols were used.
e
Synlett 2006, No. 8, 1161–1164 © Thieme Stuttgart · New York

LETTER
Sulfur-Catalyzed Oxidative Carbonylation of Primary Amines
1163
to aliphatic amines such as n-propylamine and 2-(1-cyclo- In conclusion, we have successfully developed a highly
hexenyl)ethylamine, providing the corresponding ureas in efficient sulfur-catalyzed oxidative carbonylation process
high conversion and selectivity (>99%). However, the re- that converts amines and b-amino alcohols into ureas and
activity for hindered amines such as cyclohexylamine was 2-oxazolidinones, respectively, under relatively mild re-
poor (Table 1, entry 8) and this could be ascribed to a action conditions. Moreover, a reaction mechanism was
large steric effect in such a system. It was very disappoint- proposed, in which the in situ reoxidation of H S to sulfur
2
ing that the present methodology could not be applied to by NaNO played a crucial role in the catalytic oxidative
2
aromatic amines (Table 1, entry 11) and secondary carbonylation cycle.
aliphatic amines.
The mechanism of the oxidative carbonylation of amine
was not well understood. Based on the previous find-
Acknowledgment
1
0
The study was financially supported by the Natural Science Found-
ation of China (No. 20402017).
ings, a possible mechanism of this novel S/NaNO cata-
2
lytic oxidative carbonylation process was proposed
(
Scheme 1). Initial formation of carbonyl sulfide from
carbon monoxide and sulfur followed by condensation of References and Notes
carbonyl sulfide with aliphatic amine yielded an amine
thiolcarbamate. This intermediate then decomposed to
(
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2
the in situ oxidation of H S to sulfur was catalyzed by
2
NaNO , which was the key step for this catalytic reaction.
2
O
(
(
RNH2
H+
+
RHN
S
O
COS
RHN
H+
SH
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7
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O
(
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NHR
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(
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Scheme 1 Catalytic mechanism
Interestingly, it was found that this highly efficient sulfur-
catalyzed oxidative carbonylation process was perfectly
applicable to primary amino alcohols, affording the corre-
sponding 2-oxazolidinones in high selectivity and under
the optimized reaction conditions (Table 1, entries 12–
(
d) Abla, M.; Choi, J.-C.; Sakakura, T. Green Chem. 2004,
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(
(
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1
5). As can be seen, quantitative conversions of the four
different b-amino alcohols could be realized. To our
knowledge, this process was the first example to synthe-
size 2-oxazolidinones using a catalytic amount of sulfur as
catalyst.
(7) (a) Shi, F.; Deng, Y.; SiMa, T.; Yang, H. Tetrahedron Lett.
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(
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A limitation associated with using CO/O as reagents in
organic synthesis was the potential danger of operating
the reaction at high reaction temperatures and pressures.
In our catalyst system, NaNO was used as the oxidant
thereby avoiding the use of oxygen, so our catalytic sys-
tem eliminated the potential dangers associated with the
2
2
(
e) Gabriele, B.; Salerno, G.; Brindisi, D.; Costa, M.;
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2
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1
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1
Synlett 2006, No. 8, 1161–1164 © Thieme Stuttgart · New York

1
164
X. Peng et al.
LETTER
(
10) (a) Franz, R. A.; Applegath, F. J. Org. Chem. 1961, 26,
304. (b) Franz, R. A.; Applegath, F.; Morriss, F. V.;
(12) General Experimental Procedure.
3
All oxidative carbonylation experiments were carried out in
a 100 mL autoclave equipped with magnetic stirring and
automatic temperature control. The amine or ethanolamine
Baiocchi, F. J. Org. Chem. 1961, 26, 3306. (c) Franz, R. A.;
Applegath, F.; Morriss, F. V.; Baiocchi, F.; Bolze, C. J. Org.
Chem. 1961, 26, 3309. (d) Franz, R. A.; Applegath, F.;
Morriss, F. V.; Baiocchi, F.; Breed, L. W. J. Org. Chem.
(20 mmol), sulfur (1 mmol), NaNO (10 mmol), and MeOH
2
(6 mL) were charged into the reactor. Then, the autoclave
was flushed three times with CO and pressurized with CO to
a pressure of 40 atm. The autoclave was placed in oil bath
that was preheated to 120 °C, and the whole reaction mixture
was stirred for 10 h. After the reaction, the autoclave was
cooled, excess gas was purged, and the reaction mixture was
filtered. Qualitative analyses were conducted with a HP
1
962, 27, 4341.
11) Liu, R.; Liang, X.; Dong, C.; Hu, X. J. Am. Chem. Soc. 2004,
26, 4112.
(
1
6890/5973 GCMS and quantitative analyses were carried
out over a Agilent 6820 GC (FID detector).
Synlett 2006, No. 8, 1161–1164 © Thieme Stuttgart · New York