Indium mediated reductive acylations of nitroarenes towards N,O-diacylated N-arylhydroxylamines

Article abstract of DOI:10.1081/SCC-100107004

By applying indium, Ac₂O, MeOH, and catalytic amount of InCl₃ in CHCl₃ solution, nitroarenes were transformed into N,O-diacylated N-arylhydroxylamines in moderate to excellent yields.

Full text of DOI:10.1081/SCC-100107004

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INDIUM MEDIATED REDUCTIVE ACYLATIONS OF
NITROARENES TOWARDS N,O-DIACYLATED N-
*
ARYLHYDROXYLAMINES
a
a
a
a
b
Byeong Hyo Kim , Jae Wook Cheong , Rongbi Han , Young Moo Jun , Woonphil Baik
c
&
a
Byung Min Lee
Department of Chemistry, Kwangwoon University, Seoul, 139-701, South Korea
Department of Chemistry, Myong Ji University, Kyung Ki Do, South Korea
Korea Research Institute of Chemical Technology, Taejon, South Korea
b
c
Published online: 16 Aug 2006.
To cite this article: Byeong Hyo Kim , Jae Wook Cheong , Rongbi Han , Young Moo Jun , Woonphil Baik & Byung Min Lee
*
(2001): INDIUM MEDIATED REDUCTIVE ACYLATIONS OF NITROARENES TOWARDS N,O-DIACYLATED N-ARYLHYDROXYLAMINES
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 31:23,
,
3577-3586
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SYNTHETIC COMMUNICATIONS, 31(23), 3577–3586 (2001)
INDIUM MEDIATED REDUCTIVE
ACYLATIONS OF NITROARENES
TOWARDS N,O-DIACYLATED
N-ARYLHYDROXYLAMINES*
1
Byeong Hyo Kim, Jae Wook Cheong,
,
y
1
1
Rongbi Han, Young Moo Jun,
1
2
Woonphil Baik, and Byung Min Lee
3
1
Department of Chemistry, Kwangwoon University,
Seoul, 139-701, South Korea
Department of Chemistry, Myong Ji University,
Kyung Ki Do, South Korea
Korea Research Institute of Chemical Technology,
Taejon, South Korea
2
3
ABSTRACT
By applying indium, Ac O, MeOH, and catalytic amount of
2
InCl in CHCl solution, nitroarenes were transformed into
3
3
N,O-diacylated N-arylhydroxylamines in moderate to excel-
lent yields.
*
Dedicated to Professor Jack W. Timberlake on the occasion of his 60th Birthday.
Corresponding author. E-mail: bhkim@daisy.gwu.ac.kr
y
3
577
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

ORDER
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3
578
KIM ET AL.
Recently, indium-mediated reactions have been focused on synthetic
applications because of environmental issues and the ease of reactions
obviating the need for inflammable anhydrous organic solvents and inert
1
atmosphere.
Indium was applied for the various reactions in aqueous conditions
2
without inert atmosphere; alkylation of aldehydes and ketones, reductive
3
coupling of aldimines, Reformatsky and aldol reactions, allenylation of
4
5
6
aldehydes, ring expansion of carbocycles, and reduction of some func-
7
tional groups.
Undoubtedly, indium metal can be a suitable candidate for an electron
donor in single electron transfer (SET) processes and has some striking
advantages over other metals, i.e., indium metal is stable in air or oxygen
at ordinary temperatures and is practically unaffected by water. Of the
special interest to us was the possibility of utilizing indium promoted
reaction for the preparation of N,O-diacylated N-arylhydroxylamines,
since esters of N-hydroxy-N-arylacetamides, such as ArN(OR)COCH
À
3
(
R¼COCH , SO ), are considered to be the reactive metabolites of
3
3
8
mutagenic and carcinogenic aromatic amides. In spite of their biological
interest, useful preparative methods for esters of N-hydroxy-N-arylaceta-
mides were not well established. While the direct chemical reductive diacyla-
9
,10
tions of nitroarenes were not successful,
the electrochemical reduction
of both aliphatic and aromatic nitro or nitroso compound in aprotic media
with Ac O produced N,O-diacylated hydroxylamines in yields from 40 to
2
1
0%. We previously reported Zn-mediated reductive diacylation of
1
8
nitroarenes which revealed the improved result compared to other reac-
1
tions. Herein, we wish to report on the study of efficient chemical reductive
2
one-pot N,O-diacylation reaction of nitroarenes using indium metal, InCl3
and Ac O in aprotic solvent under mild condition.
2
Various control experiments with nitrobenzene were exerted to explore
the optimum condition for the effective reductive diacylation on nitro
functional group towards Ph-N(Ac)OAc. Unfortunately, the reaction
did not proceed in the presence of Ac O/indium only (Table 1, entries 1,
2
2). To make the reaction progress, some additives seem to be needed to
activate a substrate and/or an electrophile. Thus, reactions with nitroben-
zene/Ac O (4 equiv)/In (5 equiv)/InCl (0.2equiv) were tried, and surpris-
ingly the reaction was started to take place through the influence of
2
3
a catalytic amount of InCl (entries 3–8). The reaction in aprotic solvents
3
such as THF (entry 3), CH Cl (entry 4), and CHCl (entry 8) proceeded
2
2
3
quite slowly while reactions in protic solvent system revealed fast reactions
(
entries 5–7). Protic solvent system definitely promotes the reaction.
However, because of the increased formation of undesirable acetani-
lide rather than desired N,O-diacylated product, it was required to

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NITROARENES
3579

ORDER
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3
580
KIM ET AL.
apply just minimum amount of proton source. Nitrobenzene when
was treated with Ac O (4 equiv)/In (5 equiv)/InCl (0.2equiv)/MeOH
2
3
(
2equiv) in CHCl 3 at room temperature for 20 h, gave N,O-diacylated
phenylhydroxylamine, PhN(OAc)Ac in 81% along with 13% of acetanilide
entry 10) which was the best result for the desired N,O-diacylated phenyl-
hydroxylamine.
(
We also tried several Lewis acids instead of InCl to see whether or
3
not other Lewis acids would exhibit a better result compared to InCl3.
Table 2shows the results of the reactions of nitrobenzene with several
selected Lewis acids.
InCl was found to be the best choice for our reductive diacylation.
3
Reaction with AlCl or BF resulted in relatively lower yield compared to
3
3
the reaction with InCl (Table 2, entries 2, 3) while reaction with ZnCl or
3
2
TiCl exhibited an increase of a by-product, acetanilide (entries 4, 5).
4
On the basis of these results, we have extended the diacylation reaction
to a variety of nitroarenes and results are summarized in Table 3. In most
cases, diacylations of nitroarenes were successful with fair to excellent yields.
We tried the same reaction with nitrosobenzene in place of nitrobenzene and
diacylated product 5a was obtained in 45% along with 40% of acetanilide
(
Table 3, entry 1) within an hour that implies fast formation of nitrosoben-
zene radical anion. It is clear that the acylation of nitroarenes seems to
proceed through a nitrosobenzene intermediate. Not only nitroarenes but
also nitropyridine derivative, diacylated product was obtained in a reason-
able yield (entry 10).
1
2
Similar to our previous study using Zn, nitroarenes could be
initialized by accepting an electron from indium metal since nitroarenes
have been shown the ability to form radical anions spontaneously in the
1
3
presence of electron donors. In fact, the LUMO energy level of nitroarenes
À
lies in a relatively low, thus the formation of ArNO2 can be explained
by a SET process. In addition, nitrosoarenes are also capable of accepting
an electron. Russell reported that the SET process of nitrosobenzene in the
presence of hydroxide ion occurs in > 0.5 sec to give nitrosobenzene radical
1
4
anion. In the case of nitrobenzene, reductive wave was observed at
À 0.92V that indicated nitrobenzene could be a good electron acceptor
while acetic anhydride at the same cyclic voltametric condition didn’t exhibit
1
2
any observable reduction wave. Even in the presence of InCl , reductive
3
wave of nitrobenzene was not much changed (intensity was diminished)
which indicated that InCl did not influence the electron transferring ability
3
from In to nitrobenzene. We believe the role of InCl is to increase the
3
electrophilicity of acetic anhydride by forming complexes with carbonyl
group. For mechanistic purposes, some inhibition experiments were carried
1
5a
out. In the presence of 20 mol% of 1,3-dinitrobenzene,
the reductive

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NITROARENES
3581

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3
582
KIM ET AL.
Table 3. The Reactions of Substituted Nitroarenes in the Presence of Ac O
2
(4 Equiv)/Indium (5 Equiv)/InCl
Temperature
3
(0.2Equiv)/MeOH (2Equiv) in CHCl
Ac
3
at Room
MeOH=CHCl
3
j
Ar À NO þAc O þ In þ InCl
ÀÀÀÀÀÀÀÀÀÀ ÀÀ !
2
2
3
Ar À N À OAc
rt
5
Time
(h)
Yield
(5, %)
a
Entry
1
Substrate
b
nitrosobenzene
0
3-nitrotoluene
4-nitrotoluene
1-chloro-2-nitrobenzene
1-chloro-3-nitrobenzene
1-bromo-4-nitrobenzene
1-cyano-3-nitrobenzene
1-cyano-4-nitrobenzene
2-chloro-5-nitropyridine
1
45 (5a)
5a)
2
3
4
5
6
7
8
9
0
nitrobenzene
281 (
31
48
44
19
26
1283 (
8
39 (5b)
74 (5c)
95 (5d)
93 (5e)
99 (5f)
5g)
71 (5h)
64 (5i)
c
1
6
a
GC yield with an internal standard, acetanilide was obtained as a minor product
mostly.
b
4
At 50 C.
0% of acetanilide was obtained.
ꢀ
c
acylation was retarded and the yield of N,O-diacylated product decreased to
less than 35% (20 h). Clearly, electron transfer processes through the radical
anion species are involved during the reductive acylation reaction. The poss-
ibility of radical intermediate could be excluded as the reaction of nitroben-
zene/Ac O/In/InCl at room temperature in the presence of 20 mol% of di-
2
3
1
5b–d
tert-butyl nitroxide
resulted in ineffective inhibition. Thus radical anion
of nitrobenzene generated from the electron transfer from In to nitroben-
zene may react rapidly as a nucleophile towards the acetic anhydride elec-
trophile activated by InCl to form a reactive intermediate followed by an
3
electron transfer and the loss of acetate anion to produce the nitroso inter-
mediate. With similar continuous electron transfer and acylation, the
nitroso intermediate could be transformed to N,O-diacylated N-arylhydrox-
ylamine.
In conclusion, we have now established a mild and novel reaction
route for N,O-diacylated N-arylhydroxylamines by using Ac O/In/InCl /
MeOH in CHCl which would be a useful chemical method for the reductive
2
3
3
diacylation of nitroarenes.

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NITROARENES
3583
EXPERIMENTAL
A Typical Procedure for the
N,O-Diacetylation of Nitroarenes
Indium powder 574 mg (5 mmol), indium trichloride 44 mg (0.2mmol)
and CHCl3 (4 mL) were placed in 20 mL vial equipped with a rubber
septum. Acetic anhydride 0.38 mL (4 mmol) and MeOH 0.05 mL (2mmol)
were added to the reaction mixture followed by nitroarene (1 mmol).
The mixture was stirred under nitrogen at room temperature. After the
reaction was completed, the mixture was quenched with 10% NH Cl
4
and was extracted with CH Cl (50 mL ꢁ 3). The combined CH Cl extract
2
2
2
2
was dried over MgSO and the solvent was evaporated. The GC yield was
4
determined with an internal standard and if necessary, the products
were isolated by flash column chromatography with ethyl acetate–hexane
co-solvent.
N,O-Diacetylphenylhydroxylamine (5a)12
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.37; H NMR (300 MHz,
f
1
3
CDCl ) d 7.46–7.39 (m, 5H), 2.17 (s, 3H), 2.04 (s, 3H); C NMR (125 MHz,
3
CDCl ) d 167.8, 139.3, 129.4, 128.3 (bd), 21.5, 18.8; IR (nujol) 3059, 2993,
3
À1
þ
1
803, 1694, 1600, 1496 cm ; GC-MS m/z (rel. intensity) 193 (M , 3), 151
(
94), 109 (100); HRMS (EI) calcd for C H NO 193.0739, found 193.0754.
3
1
0
11
N,O-Diacetyl-3-methylphenylhydroxylamine (5b)12
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.39; H NMR (300 MHz,
f
CDCl ) d 7.34–7.21 (m, 4H), 2.38 (s, 3H), 2.19 (s, 3H), 2.06 (s, 3H);
3
1
3
C NMR (125 MHz, CDCl ) d 167.7, 166.6, 139.4, 139.1, 130.6, 130.4,
3
1
1
1
29.1, 125.1, 21.3, 21.0, 18.2; IR (nujol) 3057, 2992, 1799, 1688,
þ
À1
378 cm ; GC-MS m/z (rel. intensity) 207 (M , 1), 165 (66), 123 (100),
05 (40); HRMS (EI) calcd for C H NO 207.0895, found 207.0899.
1
1
13
3
N,O-Diacetyl-4-methylphenylhydroxylamine (5c)12
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.39; H NMR (300 MHz,
f
CDCl ) d 7.36–7.34 (d, 2H, J ¼ 6.5 Hz), 7.24–7.22 (d, 2H, J ¼ 8.6 Hz), 2.38
3
1
3
(
s, 3H), 2.18 (s, 3H), 2.03 (s, 3H); C (125 MHz, CDCl ) d 167.8, 136.8,
3

ORDER
REPRINTS
3
584
KIM ET AL.
1
1
32.2, 130.1, 128.2, 21.4, 21.1, 18.2, IR (nujol) 3063, 2992, 1799, 1688, 1427,
À1
þ
284 cm ; GC-MS m/z (rel. intensity) 207 (M , 3), 165 (82), 123 (100), 105
(
100); HRMS (EI) calcd for C H NO 207.0895, found 207.0888.
11 13 3
N,O-Diacetyl-2-chlorophenylhydroxylamine (5d)11c
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.30; H NMR (300 MHz,
f
1
3
CDCl ) d 7.65–7.00 (m, 4H), 2.14 (s, 3H), 2.00 (s, 3H); C (125 MHz,
3
CDCl ) d 168.6, 167.6, 136.6, 132.0, 130.6, 129.0, 127.4, 124.8, 20.8, 18.1;
3
À1
IR (nujol) 3073, 2938, 1797, 1702, 1476 cm ; GC-MS m/z (rel. intensity)
þ
2
9
29 (1), 227 (M , 3), 187 (23), 185 (69), 145 (35), 143 (100) 125 (27), 101 (4),
9 (14); HRMS (EI) calcd for C H ClNO 227.0349, found 227.0344.
1
0
10
3
N,O-Diacetyl-3-chlorophenylhydroxylamine (5e)
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.23; H NMR (300 MHz,
f
1
3
CDCl ) d 7.38 (s, 1H), 7.27–7.19 (m, 3H), 2.10 (s, 3H); 1.98 (s, 3H);
C
3
(
IR (nujol) 3057, 2987, 1804, 1695, 1429 cm ; GC-MS m/z (rel. intensity)
125 MHz, CDCl ) d 167.7, 140.1, 134.5, 130.1, 127.9, 123.5 (bd), 21.3, 18.1;
3
À1
þ
2
9
29 (1), 227 (M , 3), 187 (25), 185 (74), 145 (35), 143 (100), 125 (28), 101 (3),
9 (9); HRMS (EI) calcd for C H ClNO 227.0349, found 227.0349.
1
0
10
3
N,O-Diacetyl-4-bromophenylhydroxylamine (5f)11c
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.21; H NMR (300 MHz,
f
CDCl ) d 7.56–7.53 (d, 2H, J ¼ 8.4 Hz), 7.37–7.34 (d, 2H, J ¼ 8.2 Hz), 2.20
3
1
3
(
1
s, 3H), 2.05 (s, 3H); C (125 MHz, CDCl ) d 167.8, 138.3, 132.5, 131.0,
30.7, 21.4, 18.3; IR (nujol) 3093, 2933, 1799, 1696, 1486 cm ; GC-MS m/z
3
À1
(
(
rel. intensity) 231 (48), 229 (50), 189 (65), 187 (68), 172 (20), 171 (100), 170
22), 169 (94) 90 (43); HRMS (EI) calcd for C H BrNO 270.9844, found
1
0
10
3
270.9852.
N,O-Diacetyl-3-cynophenylhydroxylamine (5g)
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.20; H NMR (300 MHz,
f
CDCl ) d 7.74 (s, 1H), 7.71–7.67 (m, 1H), 7.49–7.44 (m, 2H), 2.23 (s, 3H),
3
1
3
2
.12 (s, 3H); C (125 MHz, CDCl ) d 168.6, 167.5, 139.6, 129.8, 126.8,
3
123.3, 122.2, 117.5, 112.9, 21.3, 18.2; IR (nujol) 3053, 2991, 2233, 1808, 1699,

ORDER
REPRINTS
NITROARENES
3585
À1
þ
1
421, 1282 cm ; GC-MS m/z (rel. intensity) 218 (M , 2), 176 (100), 134
(
58), 116 (18); HRMS (EI) calcd for C H N O 218.0691, found 218.0687.
1
1
10
2
3
N,O-Diacetyl-4-cyanophenylhydroxylamine (5h)
ꢂ
White solid, mp ¼ 80.1–80.3 C; TLC (30% ethyl acetate/hexane) R
f
1
0
.26; H NMR (300 MHz, CDCl ) d 7.45 (s, 4H), 2.16 (s, 3H), 2.04 (s, 3H);
C (125 MHz, CDCl ) d 168.5, 167.9, 142.7, 133.1, 121.7, 118.2, 109.5, 21.7,
3
1
3
3
À1
1
8.2; IR (nujol) 3053, 2987, 2237, 1811, 1699, 1510, 1270 cm ; GC-MS m/z
þ
(rel. intensity) 218 (M , 3), 176 (100), 134 (85), 116 (29); HRMS (EI) calcd
for C H N O 218.0691, found 218.0681.
1
1
10
2
3
2
-Chloro-5-N,O-diacetylpyridine (5i)12
1
Liquid, TLC (30% ethyl acetate/hexane) R 0.32; H NMR (300 MHz,
f
CDCl ) d 8.49–8.48 (d, 1H, J ¼ 2.6 Hz), 7.87–7.83 (dd, 1H, J ¼ 2.6, 8.5 Hz),
3
1
3
7
.40–7.37 (d, 1H, J ¼ 8.5 Hz), 2.26 (s, 3H), 2.16 (s, 3H); C (125 MHz,
CDCl ) d 171.0, 167.8, 135.1, 133.4, 129.2, 128.7, 124.4, 21.1, 18.2; IR
3
À1
(nujol) 3063, 2983, 1810, 1703, 1612, 1425, 1266 cm ; GC-MS m/z (rel.
þ
intensity) 230 (1), 228 (M , 3), 188 (24), 186 (70), 146 (35), 144 (100), 126
(
22); HRMS (EI) calcd for C H ClN O 228.0302, found 228.0307.
9 9 2 3
ACKNOWLEDGMENTS
This work was supported by the Brain Korea 21 project and partly by
Kwangwoon University in the year 2000.
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8
Received in Japan December 25, 2000

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