Addition of carboxyalkyl radicals to alkenes through a catalytic process, using a Mn(II)/Co(II)/O2 redox system

Article abstract of DOI:10.1021/jo034584+

A novel strategy for production of mono- and dicarboxylic acids by the addition of carboxyalkyl radicals to alkenes and dienes, respectively, was successfully developed through a catalytic process with use of Mn(II)/Co(II)/O₂ system. Thus, a variety of carboxylic acids were prepared by the reaction of alkenes and dienes with acid anhydrides in the presence of a very small amount of Mn(OAc)₂ (0.5 mol %) and Co(OAc)₂ (0.1 mol %) under dilute dioxygen.

Full text of DOI:10.1021/jo034584+

Ad d ition of Ca r boxya lk yl Ra d ica ls to Alk en es th r ou gh a Ca ta lytic
P r ocess, Usin g a Mn (II)/Co(II)/O2 Red ox System
Koji Hirase, Satoshi Sakaguchi, and Yasutaka Ishii*
Department of Applied Chemistry, Faculty of Engineering and High Technology Research Center,
Kansai University, Suita, Osaka 564-8680, J apan
ishii@ipcku.kansai-u.ac.jp
Received May 6, 2003
A novel strategy for production of mono- and dicarboxylic acids by the addition of carboxyalkyl
radicals to alkenes and dienes, respectively, was successfully developed through a catalytic process
with use of Mn(II)/Co(II)/O2 system. Thus, a variety of carboxylic acids were prepared by the reaction
of alkenes and dienes with acid anhydrides in the presence of a very small amount of Mn(OAc)2
(0.5 mol %) and Co(OAc)2 (0.1 mol %) under dilute dioxygen.
Carbon-carbon bond-forming reactions through carbon
radical generation by the action of higher valence transi-
tion metal ions such as Mn(III), Co(III), Cu(II), Fe(III),
Ag(II), Pb(IV), Ce(IV), etc., are used as a powerful means
in organic synthesis.1 Among many metal oxidants,
Mn(III) is often used as a unique oxidant for a variety of
synthetic reactions. Pioneering work in this chemistry
has been done by Bush and Finkbeiner2 and Heiba and
Dessau,3 who reported that the oxidative addition of
acetic acid to alkenes in the presence of Mn(OAc)3
produces γ-lactones. In this reaction, acetic acid is
oxidized by Mn(OAc)3 to a carboxymethyl radical, which
adds to an alkene to form an adduct radical. Subsequent
further oxidation of the adduct radical by additional
Mn(OAc)3 affords a carbocation whose intramolecular cy-
clization gives a γ-lactone. Although the Mn(III)-medi-
ated reactions are very attractive as a synthetic tool, a
serious drawback of this method is that a large excess of
Mn(III) ions must be used to complete the reactions in
satisfactory yields. Therefore, if the Mn(III)-promoted
free-radical reactions can be carried out via a catalytic
process of the metal ions, the importance of the reactions
would vastly increase from the synthetic and environ-
mental viewpoints.
tene in the presence of very small amounts of Mn(OAc)2
(0.5mol %) and Co(OAc)2 (0.1 mol %) under atmospheric
dioxygen (1 atm) give the corresponding R-alkylated
ketones in fair to good yields.4 The application of this
system to the reaction of enolizable carbonyl compounds
such as malonates with alkenes led to adducts in which
alkyl groups are incorporated to the R-position of mal-
onates.5
In this paper, we wish to report a novel catalytic
method for the synthesis of mono- and dicarboxylic acids
by the addition of carboxyalkyl radicals, generated in situ
from acid anhydrides, using a Mn(II)/Co(II)/O2 redox
couple, to alkenes (eq 1).
The reaction of propionic anhydride (1) with 1-decene
(2) was chosen as a model reaction and was carried out
under various conditions to confirm optimum reaction
conditions (Table 1).
Recently, we have succeeded in catalytic free-radical
addition of ketones to alkenes using a Mn(II)/Co(II)/O2
redox system. Thus, R-keto radicals derived from ali-
phatic and cyclic ketones added to alkenes such as 1-oc-
2 (1 mmol) was allowed to react in 1 (60 mmol) without
solvent in the presence of Mn(OAc)2 (5 µmol, 0.5 mol %)
and Co(OAc)2 (1 µmol, 0.1 mol %) under a mixed gas of
O2 (0.1 atm) and N2 (0.9 atm) at 130 °C for 5 h followed
by hydrolysis with aqueous sulfuric acid to give 2-meth-
yldodecanoic acid (3) in 90% yield (Run 1). This is the
successful carboxyalkyl radical addition to alkenes through
a catalytic process. When the amount of 1 decreased to
30 and 15 equiv, the yield of 3 decreased to 86% and 74%
(1) (a) Renaud, P.; Sibi, M. P. Radicals in Organic Synthesis; Vol.
1, Basic principles; Vol. 2, Applications; Wiley-VCH: New York, 2001.
(b) Motherwell, W. B.; Chich, D. Free Radical Chain Reactions in
Organic Synthesis; Academic: London, UK, 1992. (c) Curran, D. P.
Comprehensive Organic Synthesis; Trost, B., Fleming, M. I., Eds.;
Pergamon: Oxford, UK, 1991; Vol. 4, Chapters 4.1 and 4.2. (d) Giese,
B. Radicals in Organic Synthesis: Formation of Carbon-Carbon
Bonds; Pergamon Press: Oxford, UK, 1986. (e) Migs, W. J .; de J onge,
C. R. H. I. Organic Synthesis by Oxidation with Metal Compounds;
Plenam Press: New York, 1986.
(2) (a) Finkbeiner, H. L.; Bush, J . B., J r. Discuss. Faraday Soc. 1968,
46, 150. (b) Bush, J . B, J r.; Finkbeiner, H. L. J . Am. Chem. Soc. 1968,
90, 5903.
(4) Iwahama, T.; Sakaguchi, S.; Ishii, Y. Chem. Commun. 2000,
(3) (a) Heiba, E. I.; Dessau, R. M.; Koehl, W. J ., J r. J . Am. Chem.
Soc. 1969, 91, 138. (b) Heiba, E. I.; Dessau, R. M.; Koehl, W. J ., J r. J .
Am. Chem. Soc. 1968, 90, 5905.
2317.
(5) Hirase, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. J . Org. Chem.
2002, 67, 970.
10.1021/jo034584+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/24/2003
5974
J . Org. Chem. 2003, 68, 5974-5976

Addition of Carboxyalkyl Radicals to Alkenes
TABLE 1. Rea ction of P r op ion ic An h yd r id e (1) w ith
1-Decen e (2) Ca ta lyzed by Mn (OAc)2/Co(OAc)2/O2 u n d er
Va r iou s Con d ition sa
SCHEME 1
run
1 (mmol) solvent/(mL) temp.(°C) conv (%) 3 (%)b
1
2
3
60
30
15
30
30
30
30
30
15
30
-
130
130
130
130
130
100
100
130
130
130
>99
>99
>99
>99
>99
10
96
91
78
70
90
86
74
83
70
-
80
71
49
37g
-
-
4c
5d
6e
7e,f
8
-
-
-
-
EtCOOH/2
EtCOOH/2
MeCOOH/2
9
10
a
1-Decene (2) (1 mmol) was reacted with propionic anhydride
(1, 15-60 mmol) in the presence of Mn(OAc)2 (5 µmol) and
Co(OAc)2 (1 µmol) under 0.1 atm of O2 and 0.9 atm of N2 at 130
b
°C for 5 h. Based on 1 used. c The reaction was run under air.
d
The reaction was run under 0.5 atm of O2 and 0.5 atm of N2.
e The reaction was run at 100 °C. f Mn(OAc)2 (50 µmol) and
g
Co(OAc)2 (20 µmol) were used. Dodecanoic acid (6%) was ob-
The reaction with a stoichiometric amount of Mn(OAc)3
in place of the Mn(II)/Co(II)/O2 redox couple afforded 3
(11%) and 3-octyl-γ-butyrolactone (20%), which is formed
through the well-known one-electron oxidation of the
adduct radical by Mn(OAc)3 followed by the intramolecu-
lar cyclization (eq 2).3
tained.
yields, respectively (Runs 2 and 3). The reaction under
air led to 3 in 83% yield (Run 4). However, the reaction
under a pressure of 0.5 atm of O2 and 0.5 atm of N2
resulted in considerable decrease of 3, owing to the
formation of unidentified polymeric products (Run 5).
Although the addition was difficult at 100 °C under these
conditions, 3 was obtained in 80% yield when Mn(OAc)2
(50 µmol, 5 mol %) and Co(OAc)2 (20 µmol, 2 mol %) were
used (Runs 6 and 7). No coupling product was obtained
when propionic acid was employed in place of propionic
anhydride 1 (Run 8). It is interesting to note that the
reaction in the presence of acetic acid produced 3 together
with a small amount (6%) of dodecanoic acid (4) (Run 10).
Since the reaction of 2 with acetic acid did not take place
under these conditions, acetic anhydride (5), which is
thought to be generated by the exchange reaction be-
tween acetic acid and 1 during the reaction course,
reacted with 2 to form 4.
On the basis of these results, various alkenes and
dienes were allowed to react with 1 and 5 in the presence
of catalytic amounts of Mn(OAc)2 and Co(OAc)2 under
dilute oxygen at 130 °C for 5 h (Table 2).
The reaction of 5 with 2 without any solvent afforded
4 in moderate yield (56%), but the same reaction in acetic
acid led to 4 in good yield (80%) (Runs 2 and 3). 5 must
be used in excess to obtain the adduct 4 in high yield,
probably because the generation of a carboxymethyl
radical from 5 is more difficult than that of a carboxyethyl
radical from 1 by the Mn(III) ion, since the oxidation of
the methylene group of 1 takes place more easily than
that of the methyl group of 5. 1-Octene (6) reacted with
1 and 5 to produce 2-methyldecanoic acid (7) (77%) and
decanoic acid (8) (74%), respectively (Runs 4 and 5).
Similarly, a cyclic alkene like cyclooctene (9) reacted with
1 and 5 to give the corresponding adducts, 2-cyclooctyl-
propionic acid (10) (62%) and cyclooctylacetic acid (11)
(69%), respectively (Runs 6 and 7). Under these condi-
tions, norbornene (12) afforded 2-norbonylacetic acid (13)
in high yield (91%) (Run 8). It is noteworthy that 1
reacted with 1,9-decadiene (14) to lead to dicarboxylic
acid, 2,13-dimethyltetradecanedionic acid (10), in fair
yield (60%) (Run 9). This reaction provides a new simple
catalytic route to R,ω-dicarboxylic acids which are dif-
ficult to prepare by conventional methods. However, the
reaction of 5 with 14 was somewhat difficult and mono-
and dicarboxylic acids were formed in low yields (Run
10). 1,5-Cyclooctadiene (17) afforded a fused carboxylic
acid (18) (62%) rather than dicarboxylic acid (Run 11).
It is well-known that a Co(II) species reacts with
molecular oxygen to give a peroxocobalt(III) and/or su-
peroxocobalt(III) species,6 and the resulting cobalt(III)-
dioxygen complexes oxidize the Mn(II) to Mn(III), and
then the Mn(III) oxidizes 1 to a carboxyalkyl radical. A
plausible reaction path for the present reaction is il-
lustrated as Scheme 1.
The reaction is initiated by the generation of Co(III)-
dioxygen complexes from Co(II) and O2, and the Mn(II)
is oxidized to Mn(III) by the Co(III)-dioxygen complexes
formed. Subsequently, 1 undergoes one-electron oxidation
by Mn(III) to give a carboxyethyl radical (A), which then
adds to alkene 2 to lead to an adduct radical (B). The
radical B abstracts a hydrogen atom from 1 or another
hydrogen donor to form an adduct (C) that then under-
goes hydrolysis to give 3. The formation of intermediate
C was confirmed by the GC-MS spectrum. The C was
found to be easily hydrolyzed into 3 under these condi-
tions. Although the reaction seems to proceed through a
chain process, the chain length of the reaction may be
short.
(6) (a) Basolo, F.; J ones, R. D.; Summerville, D. A. Chem. Rev. 1979,
79, 139. (b) Wong, C. L.; Switer, J . A.; Balakrishnan, K. P.; Endicott,
J . F. J . Am. Chem. Soc. 1980, 102, 5511. (c) Drago, R. S.; Cannady, J .
P.; Leslie, K. A. J . Am. Chem. Soc. 1980, 102, 6014.
J . Org. Chem, Vol. 68, No. 15, 2003 5975

Hirase et al.
TABLE 2. Rea ction of P r op ion ic An h yd r id e (1) a n d
Acetic An h yd r id e (5) w ith Va r iou s Alk en es a n d Dien es
Ca ta lyzed by Mn (OAc)2/Co(OAc)2/O2
as acrylates and acrylonitrile were employed, because
carboxyalkyl radicals which are electrophilic in nature
are undesirable for electron-poor alkenes.
a
In conclusion, we have developed a novel catalytic route
to carboxylic acids from alkenes or dienes and acid
anhydrides by using Mn(II)/Co(II)/O2 as a redox couple.
Exp er im en ta l Section
Starting materials and catalysts were purchased from
commercial sources and used without further treatment. The
products were isolated as their ester forms after the esterifi-
cation of the products with MeOH under acidic conditions, and
yields were estimated from the peak areas based on the
internal standard technique by using GC. GC analysis was
performed with a flame ionization detector, using a 0.2 mm ×
30 m capillary column (OV-17). 1H and 13C NMR spectra were
measured at 400 and 100 MHz, respectively, in chloroform-d
with Me4Si as the internal standard. Infrared (IR) spectra were
measured with NaCl or KBr pellets. GC-MS were obtained at
an ionization energy of 70 eV. The products 3,8 7,9 10,10 11,11
15,12 and 1813 are known compounds, and 4, 8, 13, and 16 are
commercially available.
P r oced u ce for Rea ction of 1 w ith 2 u n d er Dioxygen
Atm osp h er e. To a solution of 1 (60 mmol), Mn(OAc)2 (5 µmol,
0.5 mol %) and X (1 µmol, 0.1 mol %) in a two-necked flask
equipped with a balloon filled with an appropriate concentra-
tion of O2 was added 2 (1 mmol), and the mixture was stirred
at 130 °C for 5 h. After the reaction, products were subjected
to GC and GC-MS analyses.
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for Scientific Research (KAK-
ENHI) (S) (No.13853008) from the J apan Society for
Promotion of Science.
a
Substrate (1 mmol) was reacted with acetic anhydride (5) or
propionic anhydride (1) in the presence of Mn(OAc)2 (5 µmol) and
Co(OAc)2 (1 µmol) under 0.1 atm of O2 and 0.9 atm of N2 at 130
Su p p or tin g In for m a tion Ava ila ble: Experimental data.
This material is available free of charge via the Internet at
http://pubs.acs.org.
°C for 5 h. Based on 1 or 5 used. c AcOH (2.5 mL) was used as a
b
d
solvent. Dodec-11-enoic acid (18%) was obtained.
J O034584+
This shows that intramolecular cyclization of the adduct
radical takes place very fast compared with its coupling
with the carboxymethyl radical. A similar fused product
is obtained in the reaction of dimethyl malonate with 1,5-
cyclooctadiene.7 The present reaction did not take place
when alkenes bearing electron-withdrawing groups such
(8) J ayasree, S.; Seayad, A.; Chaudhari, R. V. Org. Lett. 2000, 2,
203.
(9) Monflier, E.; Tilloy, S.; Bertoux, F.; Castanet, Y.; Mortreux, A.
New J . Chem. 1997, 21, 857.
(10) Greve, B.; Imming, P.; Laufer, S. Angew. Chem., Int. Ed. Engl.
1996, 35, 1221.
(11) Ceccherelli, P.; Curini, M.; Marcotullio, M. C.; Pisani, E.; Rosati,
O.; Wenkert, E. Tetrahedron 1997, 53, 8501.
(12) Azuma, H. J P 93-245413, 1993 (AN 1995: 662976).
(13) Gates, M.; Malchick, S. P. J . Am. Chem. Soc. 1957, 79, 5546.
(7) Linker, T.; Kersten, B.; Linker, U.; Peter, K.; Peter, E.; von
Schnering, H. G. Synlett 1996, 468.
5976 J . Org. Chem., Vol. 68, No. 15, 2003