Cationic iron-catalyzed addition of carboxylic acids to olefins

Article abstract of DOI:10.1246/cl.2007.752

Cationic iron salts were found to be good catalysts for intraand intermolecular addition of carboxylic acids to olefins, which afforded the corresponding esters in good yields. Copyright

Full text of DOI:10.1246/cl.2007.752

752
Chemistry Letters Vol.36, No.6 (2007)
Cationic Iron-catalyzed Addition of Carboxylic Acids to Olefins
Kimihiro Komeyama,Ã Yasuhiro Mieno, Syotaro Yukawa, Takayuki Morimoto, and Ken TakakiÃ
Department of Chemistry and Chemical Engineering, Graduate School of Engineering, Hiroshima University,
Kagamiyama, Higashi-Hiroshima 739-8527
(Received April 5, 2007; CL-070363; E-mail: kkome@hiroshima-u.ac.jp)
Table 1. Screening of catalysta
Cationic iron salts were found to be good catalysts for intra-
and intermolecular addition of carboxylic acids to olefins, which
afforded the corresponding esters in good yields.
O
O
10 mol%catalyst
OH
O
DCE, 80 °C, 5 h
1a
2a
The importance of heterofunctionalization of unactivated
carbon–carbon multiple bonds has been widely recognized
in the field of carbon–heteroatom bond construction, and much
effort has been made towards exploitation of this methodology.1
Of the recently developed processes, late transition metal-
catalyzed reaction is a grateful tool in this area; for instance,
expensive or toxic Pt, Ir, Ag, Au, Ru, and Hg, which efficiently
coordinate carbon–carbon multiple bonds to lead to the
corresponding adducts.2 However, their reactivity for the olefin
moiety is low, that is, high temperature and long reaction time
are necessary to proceed the reaction. In 2005, Hill et al. reported
the addition of carboxylic acids with Cu(OTf)2, which allowed
participation of less bulky carboxylic acid in the reaction.3
In our previous works, simple and environmentally benign
iron salts were found to be highly active catalyst for intramolec-
ular hydroamination4 and hydroalkoxylation5 of unactivated
olefins, giving rise to a diverse set of heterocyclic compounds
in excellent yields under mild conditions. Moreover, the catalyst
activity could be improved by addition of silver salts like
AgOTf, affording cationic catalyst, Fe(OTf)3,6 which led to a
dramatically improvement of the catalytic activity.5 During
the investigation, we also found that intra- and intermolecular
addition of carboxylic acid to olefins took place effectively
in the presence of the iron catalyst. In this paper, we would
like to disclose these results.
Entry
Catalyst
Yield/%b
1
2
3
4
5
6
7
8
FeCl3
45
94
90
2
FeCl3 / 3AgOTf
FeCl3 / 3AgClO4
FeCl3 / 3AgBF4
FeCl3 / 3AgOAc
AgOTf
0
14
0
Zn(OTf)2
Cu(OTf)2
15
aConditions: 1a (0.5 mmol), DCE (5 L). NMR yield.
b
Table 2. Intramolecular addition of carboxylic acids to olefins
10 mol% FeCl3
30 mol% AgOTf
O
O
OH
O
DCE, 80 °C, 5 h
E
E
1
2
Entry
1
Substrate
Product
Yielda/%
93
O
O
OH
O
Treatment of 4-pentenoic acid (1a) with 10 mol % of FeCl3
in dichloroethane (DCE) for 5 h at 80 ꢀC afforded ꢀ-valerolac-
tone (2a) in 45% NMR yield (Entry 1, Table 1).7 Cationic iron
species Fe(OTf)3, generated in situ, completed the reaction un-
der the similar conditions, providing 2a in high yield (Entry 2).
Then, effect of counter ion on the iron was tested. OTf and ClO4
anions were effective for the transformation (Entries 2 and 3),
whereas BF4 and OAc anions afforded the product in negligible
yields (Entries 4 and 5). Other late transition-metal catalysts like
Cu(OTf)2, Zn(OTf)2, and AgOTf provided the product in lower
yields than the current catalyst (Entries 6–8).
2a
1a
OH
O
O
O
2
3
96
97
Ph
Ph
Ph
Ph
Ph
Ph
1b
OH
2b
O
O
O
Ph
Ph
2c
1c
O
Next, we tried out an expansion of the catalytic system
for the synthesis of multi-substituted ꢀ-lactones (Table 2).
Generally, the cyclization rate depends on a distance between
the donor (acid) and the acceptor (olefin) caused by the introduc-
tion of substituent(s) in the tether. However, under the present
conditions, reaction time of 1a was not so different from that
of 2,2-diphenyl-4-pentenoic acid (1b) to give the lactones 1b
and 2b in 93 and 96% isolated yield, respectively (Entries 1
and 2). The same result was obtained in the cyclization of 1c
to 2c in 97% yield (Entry 3). The system was also applicable
O
O
O
HO
OH
4
99
O
O
1d
2d
aIsolated yield.
to the synthesis of spirobicyclic ester 2d in excellent yield
(Entry 4). In addition, the heterofunctionalization of internal
olefin such as (E)-2,2-diphenyl-4-hexenoic acid was permitted
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.6 (2007)
753
Table 3. Intermolecular addition of carboxylic acids to
norbornenea
2 mol % FeCl3
6 mol % AgOTf
TsHN
TsNH2 (0.67 equiv.)
DCE, 80 °C, 20 h
2 mol % FeCl3
6 mol % AgOTf
H
O
R
O
4
99%
+
R
OH
DCE, 80 °C, 2−3 h
O
H
3
O
R1
2 mol % FeCl3
6 mol % AgOTf
Entry
Carboxylic acid
Product
3a
Yield/%b
95
O
1
2
Ph
R1COCH2COR1 (0.67 equiv.)
R1
R1 = Me (5a) 89%
87%
H
DCE, 80 °C, 12 h
2-MeC6H4
2-PhC6H4
3-MeC6H4
3,5-Me2C6H3
2,6-Me2C6H3
4-ClC6H4
3-BrC6H4
PhCH=CH
(furan-2-yl)CH=CH
Me
3b
3c
95
3
99
= Ph (5b)
4
3d
3e
95
Scheme 1.
5
99
of C–N and C–C bond with exo-selectivity though they required
long reaction time (Scheme 1).
6
3f
99
In conclusion, the cationic iron complex, Fe(OTf)3, has been
found to be a highly active catalyst for the intra- and intermolec-
ular addition of carboxylic acid to olefins under mild conditions.
Compared to previously described methods, the present catalyst
is commercially available and readily preparable material
in easy operation. Moreover, in the intermolecular addition of
acids, both aromatic and aliphatic carboxylic acids can be
employed without exception. Studies on scope and limitation
of the system and on details of the reaction path are in progress.
7
3g
3h
3i
99
8
95
9
97
10
11
12
13
14
15
3j
94
3k
94
PhCH2CH2
BrCH2
3l
97
3m
3n
3o
97
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas No. 18850015 from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
cyclohexyl
cycloheptyl
94
98
16
3p
99
References and Notes
1
a) F. Alonso, I. P. Beletskaya, M. Yus, Chem. Rev. 2004,
104, 3079. b) I. Nakamura, Y. Yamamoto, Chem. Rev.
2004, 104, 2127. c) T. E. Muller, M. Beller, Chem. Rev.
1998, 98, 675.
aConditions: RCO2H (0.5 mmol), norbornene (0.75 mmol), DCE
(1 mL). Isolated yield.
b
similarly, yielding exo-cyclized product in 71% yield along with
endo-product (28%).
2
a) Pt: H. Qian, X. Han, R. A. Widenhoefer, J. Am. Chem.
Soc. 2004, 126, 9536. b) Ir: V. H. Grant, B. Liu, Tetrahedron
Lett. 2005, 46, 1237. c) Ag: C.-G. Yang, N. W. Reich, Z. Shi,
C. He, Org. Lett. 2005, 7, 4553. d) Hg: M. J. Sofia, J. A.
Katzenellenbogen, J. Org. Chem. 1985, 50, 2331. e) G. A.
Krafft, J. A. Katzenellenbogen, J. Am. Chem. Soc. 1981,
103, 5459. f) Au: C.-G. Yang, C. He, J. Am. Chem. Soc.
2005, 127, 6966. g) Ru: Y. Oe, T. Ohta, Y. Ito, Chem.
Commun. 2004, 1620. h) T. Mitsudo, Y. Hori, Y. Watanabe,
J. Org. Chem. 1985, 50, 1566.
J. G. Taylor, N. Whittall, K. K. Hill, Chem. Commun. 2005,
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K. Komeyama, T. Morimoto, K. Takaki, Angew. Chem., Int.
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K. Komeyama, T. Morimoto, K. Takaki, Tetrahedron Lett.
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S. Ichikawa, I. Tomita, A. Hosaka, T. Sato, Bull. Chem. Soc.
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The cationic iron catalyst was also greatly effective for
intermolecular addition of carboxylic acid to norbornene
(Table 3). When benzoic acid and 1.5 equiv. of norbornene were
treated with 2 mol % of Fe(OTf)3, ester 3a was obtained in high
yield within 2 h (Entry 1). Stereochemistry of the product was
determined by NMR measurements, in which the product
was only exo-adduct.8 Bulky substituents such as 2-Me, 2-Ph,
3-Me, 3,5-Me2, and 2,6-Me2 did not inhibit the reaction, leading
to the corresponding products in satisfactory yields (Entries
2–6). Halogen-substituted benzoic acids at 4- and 3-position
were permitted similarly (Entries 7 and 8). The addition of
ꢁ,ꢂ-unsaturated carboxylic acids was also accomplished,
providing the corresponding esters in good yields (Entries 9
and 10). Surprisingly, the present system has a wide range of
synthetic scope; similar coupling products could be given from
an attack of every type of aliphatic acid to norbornene. Thus,
primary, secondary, and tertiary carboxylic acids were easily
converted to the corresponding esters in excellent yields (Entries
11–16). In addition, other nucleophiles such as amine and
diketone could easily react to norbornene, leading to formations
3
4
5
6
7
8
.
In similar conditions, when FeCl3 6H2O as a catalyst
was used, 36% yield of 2a was formed.
By Brønsted acid catalyst like TfOH the product was
provided in low yield and stereoselectivity.
Published on the web (Advance View) May 12, 2007; doi:10.1246/cl.2007.752