Catalytic one-pot synthesis of N-phenyl alkyl amides from alkene and aniline in the presence of cobalt on charcoal under carbon monoxide

Article abstract of DOI:10.1039/b201708c

N-Phenyl alkyl amides were synthesized by the cobalt on charcoal-catalyzed one-pot reaction of alkene and aniline under carbon monoxide; this is the first heterogeneous catalytic formation of N-phenyl alkyl amides.

Full text of DOI:10.1039/b201708c

Catalytic one-pot synthesis of N-phenyl alkyl amides from alkene and
aniline in the presence of cobalt on charcoal under carbon monoxide†
Sang Ick Lee, Seung Uk Son and Young Keun Chung*
School of Chemistry and Center for Molecular Catalysis, Seoul National University, Seoul 151-747, Korea.
E-mail: ykchung@plaza.snu.ac.kr; Fax: +82-2-889-0310; Tel: +82-2-880-6662
Received (in Cambridge, UK) 15th February 2002, Accepted 17th April 2002
First published as an Advance Article on the web 20th May 2002
N-Phenyl alkyl amides were synthesized by the cobalt on
charcoal-catalyzed one-pot reaction of alkene and aniline
under carbon monoxide; this is the first heterogeneous
catalytic formation of N-phenyl alkyl amides.
with amines under carbon monoxide are quite popular.2 Other
transition metal-catalysed reactions such as Pt-catalysed hydra-
tion of nitriles3 and amidation of ethylene with carbon
monoxide and ammonia over supported Ru catalysts4 have also
been reported. However, there have been no reports on the
cobalt-catalysed amidation of anilines since the cobalt car-
bonyl-catalysed formation of anilides from aniline, alkene, and
carbon monoxide reported a half-century ago.5 The reported
reaction conditions, temperatures (165–223 °C) and pressures
(320–450 atm), were too harsh to conduct the reaction in the lab.
In a continuation of the use of cobalt on charcoal (Co/C) as a
heterogeneous catalyst,6 we have become interested in amide
synthesis from aniline, olefin, and carbon monoxide and tried to
moderate the reaction conditions. Herein we report the first
heterogeneous catalytic formation of N-phenyl alkyl amides
from aniline, alkene, and carbon monoxide in the presence of
Amides represent a significant class of compounds owing to
their versatility as building blocks and intermediates for
chemical industries. A variety of elegant routes have been
discovered for the synthesis of amides.1 Normally, such
compounds are prepared by carbonylation of amines with
carbon monoxide and through amidation of alkenes or alkynes
with carbon monoxide and amines. In particular, Pd-catalysed
syntheses of amides from arylic, vinylic, or allenic substrates
† Electronic supplementary information (ESI) available: characterization of
new compounds. See http://www.rsc.org/suppdata/cc/b2/b201708c/
Table 1 Amidation of various alkenes with anilinea
Entry
Substrate
Product
Yield (%)b
1
2
1A
1A
90
70
3
4
3A
4A
84
80
5
6
5A
6A
50
74
7
8
7A
35
8A
2c
9
9A
30
10
10A
54e
23f
a 6 mmol alkene, 3 mmol aniline, and 0.3 g Co/C used. b Isolated yields based on aniline. c B was obtained in 35% yield. d 25 atm ethylene at 25 °C used.
e In water. f In THF, B was obtained in 53% yield.
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This journal is © The Royal Society of Chemistry 2002

Co/C. Our reaction conditions (150 °C and 70 atm) are much
milder than the homogeneous reaction conditions even though
they are still harsh and the reaction times are increased.
The amidation was conducted using aniline, alkene, carbon
monoxide, and Co/C. The yield of amide is dependent upon the
solvent, reaction temperature, pressure of CO, and reaction
time. After much experimentation, the optimum conditions
were established as follows: in THF, at a temperature of 150 °C,
under a CO pressure of 70 atm, and over duration of 3 days.
Recovery and reusability of the catalyst system were tested by
carrying out consecutive cycles with the same catalyst, carefully
separated at the end of each run. However, due to the leaching
of the cobalt, the catalyst system can be reused only two
times.
We also screened other cobalt carbonyl sources such as
Co2(CO)8† (36% of 1A), Co4(CO)12 (10% of 1A), CoCl(PPh3)3
(3% of 1A), CoBr2 (trace of 1A), and colloidal cobalt
nanoparticles (46% of 1A) under the optimized condition.
However, best results were obtained in the presence of Co/C.
We have screened the amidation reaction of various alkenes
under our optimal reaction conditions (Table 1). 1-Pentene and
2-pentene gave the same product, N-phenyl pentylamide 1A, in
70–90% yields. In the case of 2-pentene, a double-bond
migration prior to amidation may occur. Co/C is effective for
the amidation of higher alkenes such as 1-hexene, 1-octene, and
1-dodecene. Co/C is also effective for cycloalkenes (entries 6
and 7), which were known to be poor substrates in the
homogeneous reaction. Aryl alkenes are rather poor substrates
(entries 8 and 9). For styrene, formanilide derived from aniline
carbonylation was isolated as a major (35% yield) product
instead of 8A. The increase of the carbon chains (entry 9)
between phenyl and vinyl groups led to an increase in the yields
of the products. Ethylene (entry 10) was a peculiar substrate.
When the amidation reaction was conducted in water solution,
a 54% yield of the product (based on the aniline) was isolated.
However, subjection of ethylene under the same conditions in
THF led to isolation of 10A and formanilide in 23% and 53%
yields, respectively.
of 23%. At first, we expected a competition between amidation
and hydroesterification. However, no hydroesterification prod-
uct was formed. When N-methylaniline was used, no product
was observed. Reaction of 3,3’-methylenedianiline yielded a
diamidation product in 68% yield. No mono-amidation product
was found. The amidation reaction was sensitive to the steric
and electronic effect of the substituent(s) on aniline.
It is known7 that three types (RNHCHO (B), RNHC(O)NHR
(C), RNCO (D)) of product can be obtained from the reaction of
primary amines with carbon monoxide, depending on the
catalyst. In our amidation reaction, the formation of A and B
was observed, but the formation of diphenylurea C (R = Ph) or
phenyl isocyanate D (R = Ph) was not observed (Scheme 1).
When B was reacted with 1-pentene under our reaction
conditions, 17% of 1A was obtained. Interestingly, treatment of
C with 1-pentene under our reaction conditions for 3 days gave
1A in 18% yield, but treatment for 6 days afforded 65% of 1A
and 18% of 1B (based on the diphenyl urea used), respectively.
For D, the reactant was recovered. The oxidative addition of
aniline followed by insertion of carbon monoxide could be a
first step. However, further investigation is needed to firmly
establish the mechanism for the present reaction.
Next we investigated amidation of 1-pentene with aniline
derivatives under the same reaction conditions (Table 2). When
3,5-dimethylaniline instead of aniline was used, the expected
product was isolated in 53% yield. When 4-aminophenol was
used, the amidation product was obtained in a rather poor yield
Scheme 1
In summary, we have demonstrated that the cobalt on
charcoal-catalysed one-pot amidation reaction of alkene and
aniline under carbon monoxide produces N-phenyl alkyl amides
in reasonable to high yields. This is the first heterogeneous
catalytic formation of N-phenyl alkyl amides. Work is in
progress on the use of Co/C in other systems.
This work was supported by grant No. 2000-2-12200-001-1
from the Basic Research Program of the Korea Science and
Engineering Foundation (KOSEF) and (1999-1-122-001-5) and
the KOSEF through the Center for Molecular Catalysis. SIL
thanks the BK21 fellowship.
Table 2 Amidation of 1-pentene with aniline derivativesa
Yield
Entry Substrate
Product
(%)b
1
2
1A
90
53
11A
Notes and references
1 (a) M. North, Contemp. Org. Synth., 1994, 1, 475; (b) G. Benz, in
Comprehensive Organic Synthesis, ed. B. M. Trost and I. Fleming,
Pergamon Press, Oxford, 1991, vol. 6, p. 381.
2 (a) K. Okura, H. Kai and H. Alper, Tetrahedron: Asymmetry, 1997, 8,
2307; (b) C. Coperet, T. Sugihara and E.-i. Negishi, Tetrahedron Lett.,
1995, 36, 1771; (c) N. D. Trieu, C. J. Elsevier and K. Vrieze, J.
Organomet. Chem., 1987, 325, 23.
3
4
12A
23
—
NR
3 T. Ghaffar and A. W. Parkins, J. Mol. Catal. A: Chem., 2000, 160,
C249.
4 S.-P. Zhao, S.-I. Sassa, H. Inoue, M. Yzmazakim, H. Watanabe, T. Mori
and Y. Morikawa, J. Mol. Catal. A: Chem., 2000, 159, 103.
5 P. Pino and R. Magri, Chim. Ind. (Milan), 1952, 34, 511; P. Pino and P.
Paleari, Gazz. Chim. Ital., 1951, 81, 64.
6 S. U. Son, S.-I. Lee and Y. K. Chung, Angew. Chem., Int. Ed., 2000, 39,
4158.
5
13A
68
7 M. B. Smith and J. March, March’s Advanced Organic Chemistry, 5th
edn., Wiley-Interscience, New York, 2001, p. 820 and references
therein.
a 6 mmol alkene, 3 mmol aniline derivatives, and 0.3 g Co/C used. b Isolated
yields.
CHEM. COMMUN., 2002, 1310–1311
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