Selenium-catalyzed reductive carbonylation of 2-nitrophenols to 2-benzoxazolones

Article abstract of DOI:10.1002/ejoc.200400561

2-Benzoxazolones or 2-benzimidazolones are synthesized in moderate to good yields in the presence of a base (KOH, NaOH, KOAc, NEt₃, DBU) at atmospheric pressure or under a high pressure of CO by one-pot reductive carbonylation of 2-nitrophenols or 2-nitroaniline in the presence of selenium as catalyst. Besides the effect of base, the effects of solvent and temperature on the reaction were investigated at high or atmospheric pressure. Contrasting results were obtained for 2-benzoxazolones or 2-benzimidazolone at high and atmospheric pressures. Moreover, phase-transfer catalysis was exhibited. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejoc.200400561

FULL PAPER
Selenium-Catalyzed Reductive Carbonylation of 2-Nitrophenols to
2-Benzoxazolones
Xiaofang Wang,[a] Gang Ling,[a] Yan Xue,[a] and Shiwei Lu*[a]
Keywords: Carbonylation / Nitrophenols / Phase-transfer catalysis / Reduction / Selenium
2-Benzoxazolones or 2-benzimidazolones are synthesized in
moderate to good yields in the presence of a base (KOH,
NaOH, KOAc, NEt3, DBU) at atmospheric pressure or under
a high pressure of CO by one-pot reductive carbonylation of
2-nitrophenols or 2-nitroaniline in the presence of selenium
as catalyst. Besides the effect of base, the effects of solvent
and temperature on the reaction were investigated at high
or atmospheric pressure. Contrasting results were obtained
for 2-benzoxazolones or 2-benzimidazolone at high and at-
mospheric pressures. Moreover, phase-transfer catalysis was
exhibited.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
yield as high as 96%.[9] In the carbonylation of α,ω-di-
amines to 2-imidazolidinones using W(CO)6 as the catalyst,
yields were low.[10,11] A reaction catalyzed by elemental
selenium has been reported to produce high yields, but
stoichiometric or excess amounts of selenium are
required.[12–15]
Introduction
2-Benzoxazolones and their derivatives are useful inter-
mediates in the production of pharmaceuticals, pesticides,
and
herbicides.[1]
For
example,
cyclohexylami-
nobenzoxazole derivatives are antagonists of N-methyl-d-
aspartate (NMDA) receptors and are useful for treating
stroke, cerebral ischemia, depression, immune diseases
etc.[2] Additionally, 2-benzoxazolone derivatives have found
use as achiral templates for enantioselective Diels–Alder re-
actions,[3] and chiral oxazolidin-2-ones are widely used as
chiral auxiliaries in many important asymmetric synthe-
ses.[4] These compounds are currently produced by the reac-
tion of phosgene with o-aminophenols or o-phenylenediam-
ines.[5] However, because phosgene is highly toxic and cor-
rosive, it is important to develop a non-phosgene reaction.
Several other synthetic methods have also been reported.
For example, the carbonylation of o-aminophenols or o-
phenylenediamines with dimethyl carbonate (DMC) affords
2-benzoxazolones or 2-benzimidazolones,[6] while dialkyl
carbonates are obtained from the oxidative carbonylation
of alcohols with carbon monoxide.[7] Clearly, the synthesis
of 2-benzoxazolones or 2-benzimidazolones starting di-
rectly from carbon monoxide rather than from dialkyl car-
bonates represents an advantage from the standpoint of
atom economy.[8]
Oxidative carbonylation requires an oxidant, and in most
cases the oxidant is oxygen. However, mixing CO and O2
is dangerous, therefore reductive carbonylation has recently
attracted attention owing to the avoidance of using O2. The
transition-metal-catalyzed synthesis of heterocyclic-con-
taining nitrogen compounds by the reductive carbonylation
of o-substituted nitrobenzenes with carbon monoxide is a
well-established method. A heterogeneous, bimetallic Fe–Pd
complex catalyzes the carbonylation of 2-nitrophenol under
200 atm pressure of CO with high yields.[16,17] Additionally,
the ruthenium- or palladium-catalyzed reductive carbon-
ylation of o-nitrobenzylalcohols gives the corresponding
1,4-dihydro-2H-3,1-benzoxazin-2-one derivatives.[18] 2-
Benzoxazolone can also be prepared in high yields by re-
ductive carbonylation of 2-nitrophenol with a high pressure
of carbon monoxide and a stoichiometric amount of sulfur
or selenium in water in the presence of NEt3.[19,20]
We recently reported a new method for the synthesis of
unsymmetrical ureas by direct selenium-[21] or selenium di-
oxide-catalyzed[22,23] reductive carbonylation of nitroaro-
matics and amines or anilines under 30 atm of CO pressure
with the organic base NEt3 as co-catalyst. In the course of
our ongoing investigation of the selenium-catalyzed re-
ductive carbonylation of 2-nitrophenols, we have discovered
that the organic bases NEt3, DBU, and N-methylpyrroli-
dine[24,25] assist the reaction under high pressures of CO. In
this work the carbonylation of 2-nitrophenol or 2-nitroani-
line derivatives is studied in the presence of organic (NEt3,
DBU) or inorganic bases (KOH, NaOH, NaOAc, KOAc)
The conversion of 2-aminophenols to 2-benzoxazolones
has been achieved by using PdI2 in conjunction with KI as
the catalytic system in 1,2-dimethoxyethane (DME); under
the optimized conditions, 2-benzoxazolinone formed with a
[a] Dalian Institute of Chemical Physics, Chinese Academy of
Sciences,
161 ZhongShan Road, Dalian, Liaoning, 116011, P. R. China
Fax: +86-411-8369-8749
E-mail: lusw@dicp.ac.cn
Eur. J. Org. Chem. 2005, 1675–1679
DOI: 10.1002/ejoc.200400561
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1675

X. Wang, G. Ling, Y. Xue, S. Lu
FULL PAPER
under atmospheric pressure and low temperature or high Table 1. Effect of base and solvent on the reductive carbonylation
of 2-nitrophenol.
temperatures and pressures. A possible reaction pathway of
Yield[a] [%]
carbonylation was assumed. The results of the detailed in-
vestigation are reported here.
Entry
Solvent
Base
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DMF
DMF
DMF
DMF
DMF
NEt3
DBU
KOH
NaOH
NaOAc
KOAc
KOH
Ͻ3
16
91
68
12
93
86
–
Results and Discussion
In a previous paper on selenium-catalyzed reductive car-
bonylation of 2-nitrophenol,[24] the products were obtained
under high pressure of CO and at high temperature in the
presence of organic bases. These were promising but unop-
timized results. The system has subsequently been explored
more thoroughly. Variables such as the nature of the base,
the quantity of base added, CO pressure, solvent, and tem-
perature have now been examined and the results are de-
scribed below.
DMF
DMSO
toluene
toluene
toluene
toluene
toluene
toluene
DMF
KOH
[b]
NEt3[c]
–
NEt3
DBU[d]
45
57
67
38
Ͻ3
Ͻ3
21
NEt3 + DBU[e]
KOH[f]
NEt3
DMF
DMF
KOH[f]
KOH[g]
[a]
Isolated yields. Reaction conditions: 2-nitrophenol (5.0 mmol),
solvent (15 mL), base (6.0 mmol), selenium (0.4 mmol), T = 110 °C,
pCO = 1 atm, t = 4 h. [b]T = 95 °C.
Solvent (10 mL), base
[c]
(20 mmol), 2-nitrophenol (10 mmol), selenium (0.5 mmol), T =
[d]
150 °C, pCO = 30 atm, t = 7 h.
Base (10 mmol); DBU = 1,8-
[e]
diazabicyclo[5.4.0]undec-7-ene.
NEt3 (20 mmol)
+
DBU
[f]
[g]
(10 mmol). Base (6 mmol), t = 4 h.
As for [a] except for the
The base plays an important role during the reaction. It
is well known that organic bases such as NEt3 and DBU
assist the selenium-based catalytic system,[12–15,21,23–26] but
in this work, as shown in Table 1, both NEt3 and DBU do
not demonstrate efficient activity under atmospheric pres-
sure of CO (Table 1, entries 1 and 2), presumably partially
due to their high volatility and quick evaporation under
atmospheric pressure, resulting in low yields of 2-benz-
oxazolone (2a, X = O). The yields were 3% and 16%,
respectively. Inorganic bases such as KOH and KOAc were
much more efficient for the reductive carbonylation under
atmospheric pressure; the yields were 91% and 93%,
respectively (Table 1, entries 3 and 6). For comparison pur-
poses, the experiments were run under identical conditions
except for the pressure of CO (Table 1, entries 3 and 16); the
yield of 2-benzoxazolone (2a) under 30 atm of CO pressure
(21%) was much less than that under atmospheric pressure
(91%). The choice of solvent also turned out to be signifi-
cant (Table 1, entries 3, 7, 8 and 10, 13, 14, 15). We ob-
served that selenium is insoluble in toluene when KOH or
NEt3 are used as base under atmospheric pressure of CO.
pressure of CO. The reaction conditions of entries 11–15 are the
same as those of entry 10 except for the note.
Table 2.Effects of the amounts of base, DMF, and the temperature
on the reductive carbonylation of 2-nitrophenol under 1 atm of CO
pressure.
Entry
KOH
[mmol]
DMF
[mL]
Temp.
[°C]
Yield[a]
[%]
1
2
3
4
5
6
7
8
9
2.0
3.0
6.0
10.0
3.0
3.0
3.0
3.0
3.0
3.0
15
15
15
15
15
110
110
110
110
125
95
95
95
95
80
25
86
91
55
91
73
90
91
66
74
6[b]
10[c]
15[b]
20[b]
15[b]
10
[a]
Isolated yields. Reaction conditions: 2-nitrophenol (5.0 mmol),
selenium (0.4 mmol) t = 4 h. [b]t = 8 h.[c]t = 12 h.
The yield of 2-benzoxazolone was improved by the ad-
Polar solvents such as DMF and DMSO were essential for dition of an excess of DMF (Table 2, entries 6–9). It was
the reaction under atmospheric pressure. Under high pres- necessary to employ dilute solutions under atmospheric
sure NEt3 and DBU with apolar toluene as solvent gave pressure of CO to avoid intermolecular reactions. With a
the product in 45% and 57% yields, respectively (Table 1, fixed amount of catalyst, a more dilution solution did not
entries 10, 11, and 12), and the inorganic base KOH was improve the efficiency of the reaction (Table 2, entry 9).
also useful in 38% yield (entry 13), although with DMF as Note that the reactions were run at 80–130 °C (Table 2, en-
solvent the yields of 2-benzoxazolone were dramatically tries 2, 5, 8, and 10). The solvent was evaporated at higher
lower (Table 1, entries 15 and 16).
As seen in Table 2, the yields of 2a increased as the for example, the yield of 2a was 34% at 50 °C after 8 hours.
amount of KOH was increased to six equivalents, and then Further studies with 2-nitrophenol derivatives 1b, 1c, and
temperature. A low temperature resulted in a slow reaction;
decreased with any further increase of the amount of KOH. 1d probed the effect of the position of methyl substitution
Increasing the amount of added KOH from two equivalents on the formation of 2-benzoxazolones (Table 3). In contrast
to six equivalents, the yields increased significantly from to the results with the substrate 1a, the yields of 2c and 2d
25% to 91%. The reaction proceeds very slowly in the pres- were higher under a high pressure of CO, but the yield of
ence of a small amount of base (Table 2, entry 1).
2b was the same as that of 2a, which shows that the nearer
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Selenium-Catalyzed Reductive Carbonylation of 2-Nitrophenols
FULL PAPER
Table 3. Reductive carbonylation of 2-nitrophenols under high or atmospheric pressure.
[a]
Isolated yields. Reaction condition: toluene (10 mL), 2-nitrophenol (10 mmol), selenium (0.5 mmol), NEt3 (20 mmol) + DBU
[b]
(10 mmol), T = 150 °C, t = 7 h. 2-Nitrophenol (5 mmol), DMF (15 mL), KOH (6 mmol), selenium (0.4 mmol), T = 110 °C, t = 4 h.
the methyl group is to the nitro group, the lower the yield.
During the reaction process phase transfer of the Se cata-
This could be because the methyl group causes steric hin- lyst occurs.[23,24,26] Before the introduction of CO into the
drance to the nitro group. In addition, an intermolecular reaction mixture, the catalytic system is heterogeneous and
reaction is prone to decrease the yields of 2-benzoxazolones. the selenium catalyst is present as a powder. Selenium has
Under atmospheric pressure of CO, the yields of 2b, 2c, and a very low solubility in most common solvents, but as the
2d were lower than that of 2a. This can be attributed to the reaction proceeds it dissolves completely and the system be-
electron-donor effect of the methyl group. The results with come a brown homogeneous solution.[32,33] When the reac-
1f show obvious differences between high- and atmo- tion is quenched by stopping bubbling CO and exposing
spheric-pressure conditions (Table 3). Under atmospheric the solution to air, the solution is oxidized to form a grey
pressure of CO, 2f is not easily obtained.[27] However, sele- precipitate of selenium, which can be easily recovered by
nium catalyzes the reaction of 2-nitrobenzyl alcohols at filtration and can be reused with a yield of 75% to give a
30 atm of CO pressure to afford 1,4-dihydro-2H-3,1- catalytic activity similar to that of fresh selenium. That is,
benzoxazin-2-ones in good yields.[25] The reason for this will the reaction system changes from heterogeneous to homo-
be investigated in the future.
geneous and then recycles to heterogeneous to allow separa-
The results with 2-nitroaniline derivatives under high tion. Therefore, this catalytic system possesses the advan-
pressure of CO are shown in Table 4; the yields of 2-benz- tages of both homogeneous and heterogeneous catalysis.
imidazolones are good to moderate. 2-Benzimidazolone
Mechanism
was also obtained under atmospheric pressure with a yield
of 57%. Compound 2l is not easy to obtain under either
high- or atmospheric-pressure conditions.
Although a detailed study of the reaction mechanism has
not been undertaken, the present reaction can be under-
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X. Wang, G. Ling, Y. Xue, S. Lu
FULL PAPER
Table 4. Reductive carbonylation of 2-nitroanilines under high pressure of CO.
[a]
Isolated yields. Reaction conditions: pCO = 30 atm; solvent: toluene; base: NEt3; time: 4 h.
stood mechanistically by assuming the reaction pathway
shown in Scheme 1. In the selenium-catalyzed reductive car-
Conclusions
In conclusion, the effect of bases, such as the organic
bases NEt3, DBU and the inorganic bases KOH and
NaOH, on selenium-catalyzed reduction carbonylation of
2-nitrophenol was investigated under atmospheric or high
pressure of CO. Contrasting results were obtained for 2-
benzoxazolones under high or atmospheric pressure of CO,
and the yields were moderate to good. A possible pathway
has been postulated. The present one-pot synthesis of 2-
benzoxazolones or 2-benzimidazolones represents a new al-
ternative to the use of phosgene.
bonylation of nitroaromatics, it is presumed that the deoxy-
genation of nitroaromatics 1 with carbonyl selenide (SeCO),
generated by the reaction of elemental selenium with car-
bon monoxide in the presence of base,[12,13] results in the
intermediate nitrene species 2,[18,23,34–36] which can react
with CO to form isocyanate 3. This isocyanate reacts fur-
ther with an amine or hydroxyl group to give the final pro-
duct 4.
Experimental Section
General Remarks: All the organic solvents were of reagent grade
and used without further purification. 2-Nitrophenols and 2-nitro-
anilines, elemental selenium (99.9%), carbon monoxide (99.9%),
and base were all used as received. Melting points were determined
on a Taike X-4 apparatus (Beijing, China) and are uncorrected. 1H
and 13C NMR spectra were obtained on a Bruker DRX 400-MHz
spectrometer. Chemical shifts are reported in ppm relative to tet-
ramethylsilane. [D6]Dimethyl sulfoxide was the solvent.
Typical Procedure for the Synthesis of 2-Benzoxazolone. General
Procedure for the 2-Nitrophenol Derivatives under High Pressure of
CO: Selenium (0.0395 mg, 0.5 mmol), 2-nitrophenol (1.39g,
10 mmol), triethylamine (2.02g, 20 mmol), DBU (1.53g, 10 mmol),
and toluene (10 mL) were successively introduced into a 100-mL,
Scheme 1.
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Eur. J. Org. Chem. 2005, 1675–1679

Selenium-Catalyzed Reductive Carbonylation of 2-Nitrophenols
FULL PAPER
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(m, 4 H) ppm. 13C NMR ([D6]DMSO): δ = 154.50 (C=O), 143.32
(Ph-O), 130.40 (Ph-NH), 123.77 (C-5), 121.84 (C-6), 109.59 (C-7),
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125 °C). H NMR (400 MHz, [D6]DMSO, 25 °C): δ = 11.56 (s, 1
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δ = 154.71 (C=O), 141.41 (Ph-O), 133.41 (Ph-NH), 130.38 (C-5),
122.56 (C-6), 110.11 (C-7), 108.99 (C-4), 20.90 (CH3) ppm.
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Received: August 06, 2004
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