N-arylamides from selenium-catalyzed reactions of nitroaromatics and amides in the presence of carbon monoxide and mixed organic bases

Article abstract of DOI:10.1002/adsc.200404077

N-Arylamides were exclusively obtained in moderate to good yields from selenium-catalyzed reactions of nitroaromatics with amides in the presence of CO and mixed organic bases Et₃N and DBU.

Full text of DOI:10.1002/adsc.200404077

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N-Arylamides from Selenium-Catalyzed Reactions of
Nitroaromatics and Amides in the Presence of Carbon Monoxide
and Mixed Organic Bases
Jinzhu Chen, Gang Ling, Zhengkun Yu,* Sizhong Wu, Xiaodan Zhao,
Xiaowei Wu, Shiwei Lu*
National Engineering Research Center of r Catalysis, Dalian Institute ofChemical Physics, Chinese Academy ofSciences,
457 Zhongshan Road, Dalian, Liaoning 116023, P. R. China
Fax: (þ86)-411-8437-9227, phone: (þ86)-411-8437-9227, e-mail: zkyu@dicp.ac.cn
Received: March 11, 2004; Accepted: July 20, 2004
Abstract: N-Arylamides were exclusively obtained in
moderate to good yields from selenium-catalyzed re-
actions ofnitroaromatics with amides in the presence
dyl)benzamide (4a) in 34% and 13% yields, respectively.
When other substituted benzamides were applied to this
catalytic reaction system, reductive carbonylation and
acylation ofthe nitro groups took place competitively
to give a mixture ofcompounds oftypes 3a and 4a
with varying ratios of 3 to 4. On using 1,8-diazabicy-
ofCO and mixed organic bases Et N and DBU.
3
Keywords: acylation; carbon monoxide; N-aryla-
mides; nitroaromatics; selenium
clo[5.4.0]undec-7-ene (DBU) instead ofEt N as the
3
co-catalyst, 4a was exclusively formed in 62% yield
from the reaction of 1a and 2 under the same conditions.
Surprisingly, 4a was obtained in a higher yield, i.e., 76%
(Table 1, entry 1) by use ofa combination ofEt 3N and
DBU as the co-catalyst.
Acylation ofaromatic compounds is an important proc-
ess in synthetic chemistry. Friedel–Crafts reaction and
The formation of N-pyridylbenzamides has never
other less common methods for acylation have been de- been reported by means ofnon-metallic selenium-cata-
veloped.[1–4] For instance, Suzuki[1] developed a new acy- lyzed reactions ofbenzamides and nitropyridines. [7–11] It
lation reaction using imidazolidenylcarbene as the cata- was also found that benzamide derivatives and substitut-
lyst and Seyferth[2] has shown the acylation ofelectro-
ed nitropyridines underwent the same type ofreactions,
philes with acyllithiums to produce a-hydroxy ketones exclusively forming the corresponding N-pyridylbenza-
and a-diketones. N-Arylamides have been widely used mides (Scheme 2 and Table 1). It is noteworthy that N-
in self-assembly processes to control dimensional prop- pyridyl-N’-benzoylureas oftype 3 were not detected
agation[5] and construction ofmodel systems of r poly-
by HPLC-MS analysis. As shown in Table 1 substituted
peptides and proteins.[6] N-Arylamides can also be pre- benzamides 1 readily reacted with nitropyridine 2 in the
pared by N-acylation ofaromatic amines with phosgene. presence ofselenium, Et 3N/DBU and carbon monoxide
We have recently reported the selenium-catalyzed re- under relatively mild conditions. Yields of 4b – e were
ductive carbonylation ofnitroaromatics to aofrd un-
good and higher than those of 4a, 4f and 4g (Table 1),
symmetrical ureas.[7] Both Sonodaꢀs[8] and our laborato- demonstrating that the reactions are electronically in-
ries[9] reported that nitroaromatics can be transformed fluenced by substituents on the aromatic rings
into anilines with CO and water using selenium as the (Scheme 2). The presence ofan intermolecular hydro-
catalyst. Herein we report the novel selenium-catalyzed gen bond in 2-chlorobenzamide and the electron-with-
synthesis of N-arylamides from formal reductive N-acy-
lation ofnitroaromatics with amides in the presence of
CO and organic bases Et3N and DBU.
Our original intention was to prepare N-pyridyl-N’-
benzoylureas by coupling reductive carbonylation ofni-
tropyridine and oxidative carbonylation ofbenzamide
in a one-pot reaction as shown in Scheme 1. Thus treat-
ment ofbenzamide ( 1a) and 2-methoxy-5-nitropyridine
(2) with carbon monoxide in the presence ofa catalytic
amount ofselenium and the co-catalyst triethylamine in
toluene at 1608C afforded N-(6-methoxy-3-pyridyl)-N’-
benzoylurea (3a) together with N-(6-methoxy-3- pyri- Scheme 1.
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DOI: 10.1002/adsc.200404077
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Jinzhu Chen et al.
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drawing property ofchloride led toa poor yield of 4f (Ta-
ble 1, entry 6).
Nicotinamide 5 and substituted nitrobenzenes 6 also
underwent the same type ofreactions to give C-pyrid-
yl-N-arylamides 7 under the same reaction conditions
(Scheme 3 and Table 2). 2-Methylnitrobenzenes gave
the highest yields (83–85%) ofthe products (Table 2,
entries 2 and 9). In other cases, the electronic properties
of the substitutent on the phenyl ring affect formation of
7.
Scheme 2.
It is worthy ofnote that both reactions described in
Scheme 4 afforded C-pyridyl-N-phenylbenzamide 8 in
good yields (84% and 89%, respectively) underthe reac-
tion conditions stated in Tables 1 and 2. Reaction ofben-
zamide (1a) and aniline to form 8 indicates that nitro-
benzene may also be reduced to aniline,[8,9] followed
by acylation with benzamide (1a) in the presence of
CO. The reaction mechanisms are proposed in Figure 1.
Nitrene (A) is proposed to be formed from ArNO2 with
in situ generated species SeCO and further reacts with
SeCO to produce isocyanate (B).[7,13]
Table 1. Formation of 4 from the reaction of substituted ben-
zamides and 2-methoxy-5-nitropyridine.
Entry R1
Product Mp [8C] (Ref.) Isolated
Yield [%]
1
H
4a
136–138
(139–140[12a]
119–120
102–103
168–169
134–136
112–114
196
76
)
2
3
4
5
6
7
2-Me
3-Me
4-Me
3,5-di-Me 4e
2-Cl
4b
4c
4d
80
81
84
87
49
68
Addition ofbenzamide to B affords ArNHCONH-
COAr’ (C). Compound C is then decomposed to the
4f
4g
4-Cl
¼ ¼
product ArNHCOAr’ and species HN C O which
¼ ¼
may be bound to selenium in the form of [HN C O]Se.
O]Se. Elemental selenium was recovered from the
Reaction conditions: Se, 0.5 mmol; substituted benzamide,
10 mmol; 2-methoxy-5-nitropyridine, 10 mmol; Et3N,
20 mmol; DBU, 10 mmol; CO, 3.0 MPa; toluene, 10 mL;
1608C, 4.0 h.
¼
mixture after the reaction had been quenched in air by
addition ofaqueous HCl, and also orfmamide
(HCONH2) from the hydrolysis of HN C O was de-
¼ ¼
tected by GC-MS analysis. Without DBU compound C
could be collected in considerable yields by use ofEt
3
N as the co-catalyst (Scheme 1) and no C could be ob-
tained when DBU was used, which indicates that the
strong organic base DBU prompts the complete decom-
position of C into the product under the reaction condi-
tions. The alternative mechanism (b) is partially attrib-
uted to the formation of product ArNHCOAr’ by in-
volvement ofwater from the reagents. Because all the
solvents and materials were used as supplied and, espe-
cially, a considerable amount ofwater is present in Et 3N
Scheme 3.
Table 2. Formation of 7 from the reaction of nicotiamide and substituted nitrobenzenes.
Entry
R2
Product
Mp [8C] (ref.)
Isolated Yield [%]
1
2
3
4
5
6
7
8
9
H
7a
7b
7c
7d
7e
7f
7g
7h
7i
116–119(118–119[12b]
)
62
83
55
57
60
56
63
41
85
46
2-Me
3-Me
4-Me
4-Et
4-OEt
4-OPh
3-Cl
103–105 (105[12c]
109–112
)
145–147
124–126
173–176 (175–176[12d]
147–149 (149–150[12e]
140–143
)
)
2-Me-3-Cl
3-Br
141–142
136–138
10
7j
Reaction conditions: Se, 0.5 mmol; nicotinamide, 10 mmol; substituted nitrobenzene, 10 mmol; Et3N, 20 mmol; DBU,
10 mmol; CO, 3.0 MPa; toluene, 10 mL; 1608C, 4.0 h.
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N-Arylamides from Selenium-Catalyzed Reactions of Nitroaromatics
COMMUNICATIONS
Experimental Section
Typical Procedure for N-(6-Methoxy-3-
pyridyl)benzamide (4a)
Selenium (39.5 mg, 0.5 mmol), benzamide (1.22 g, 10 mmol),
2-methoxy-5-nitropyridine (1.54 g, 10 mmol), triethylamine
(2.02 g, 20 mmol), DBU (1.52 g, 10 mmol) and toluene
(10 mL) were successively loaded in a 100-mL stainless-steel
autoclave. The reactor was sealed, flushed with 1.0 MPa of car-
bon monoxide for three times, pressurized with 3.0 MPa car-
bon monoxide, and then placed in an oil bath preheated to
1608C. After the reaction was complete, the apparatus was
cooled to ambient temperature, and the remaining carbon
monoxide was evacuated. The reaction mixture was poured
into aqueous 1 N HCl (50 mL), and extracted with CH2Cl2
(3ꢀ50 mL). The organic phase was dried over MgSO4, filtered
and all the volatiles were evaporated under reduced pressure.
The resultant crude product was purified by flash column chro-
matography on silica gel (v/v, hexane/EtOAc¼5:1) to afford
4a as colorless needles; yield: 1.73 g (76%); mp 136–1388C
Scheme 4.
(Lit.: 139–1408C[12a]); IR (KBr): n¼3308 (nNꢁH), 1640 (nC O),
¼
1
1578, 1510, 1485, 1450 (nC
N), 1379 cmꢁ1 (nCH ); H NMR
¼
¼
C, C
(400 MHz, CDCl3, 238C): d¼3.90 (s, 3H, OCH3),36.71 (d, J¼
8.8 Hz, 1H), 7.42 (t, J¼7.6 Hz, 2H), 7.51 (t, J¼7.2 Hz, 1H),
7.84 (d, J¼7.6 Hz, 2H), 7.95 (dd, J¼8.8, 2.8 Hz, 1H), 8.07 (s,
1H, NH), 8.25 (s, 1H); 13C{1H} NMR (400 MHz, CDCl3,
238C): d¼53.75, 110.71, 127.23, 128.80, 131.99, 132.94,
134.50, 139.45, 161.38, 166.24.
Other products were identified by NMR and HPLC-MS
measurements and/or comparison with the authentic samples.
Acknowledgements
We acknowledge financial support from the Innovation Fund-
ing of Chinese Academy of Sciences, P. R. China.
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with amides in the presence ofselenium, CO, Et 3N and
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Adv. Synth. Catal. 2004, 346, 1267–1270
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