Chelation-Assisted Hydroesterification of Alkenes Catalyzed by Rhodium Complex

Article abstract of DOI:10.1021/ol035582e

(Equation presented) The hydroesterification of alkenes with 2-pyridylmethanol (1) catalyzed by Rh₄(CO)₁₂ is described. The reaction is accelerated by the presence of a pyridine ring in the alcohol 1. The reaction is applicable to various alkenes, both terminal and internal alkenes.

Full text of DOI:10.1021/ol035582e

ORGANIC
LETTERS
2003
Vol. 5, No. 23
4329-4331
Chelation-Assisted Hydroesterification of
Alkenes Catalyzed by Rhodium Complex
Kazuhiko Yokota, Hiroto Tatamidani, Yoshiya Fukumoto, and Naoto Chatani*
Department of Applied Chemistry, Faculty of Engineering, Osaka UniVersity,
Suita, Osaka 565-0871, Japan
chatani@chem.eng.osaka-u.ac.jp
Received August 22, 2003
ABSTRACT
The hydroesterification of alkenes with 2-pyridylmethanol (1) catalyzed by Rh4(CO)12 is described. The reaction is accelerated by the presence
of a pyridine ring in the alcohol 1. The reaction is applicable to various alkenes, both terminal and internal alkenes.
We successfully developed a series of catalytic reactions
involving the cleavage of unreactive bonds, such as C-H,1
C-C,2 C-O,3 and C-F,4 by utilizing the chelation-assistance
strategy.5,6 We have already reported on a series of a
chelation-assisted carbonylation reaction at C-H bonds on
the basis of the methodology that heteroatom-directing
groups promote the cleavage of C-H bonds.7 In all cases,
the substrates require the presence of an sp2 nitrogen as the
directing group at the appropriate position. The results
indicate that the coordination of the sp2 nitrogen to the metal
center is a key step for the reaction to proceed. Next, we
turned our attention to the cleavage an O-H bond in alcohols
in order to utilize the O-H bond in the hydroesterification
of alkenes. The hydroesterification of alkenes is an important
process for both industrial and laboratory scales.8 Although
a variety of late transition metal complexes are known to be
active, Co and Pd complexes are most frequently used as a
catalyst. However, Co-catalyzed reactions require harsh
reaction conditions (usually >140 °C and >100 atm of CO).
Though Pd-catalysis can make the reaction temperature low
(70-140 °C), the reaction needs 40-120 atm of CO yet.
Moreover, 1,1- and 1,2-disubstituted alkenes give hydro-
esterified products in relatively lower yield. This result is in
contrast to that of monosubstituted alkenes, which give the
products in high yield. We wish to report that the Rh-
catalyzed hydroesterification of terminal and internal alkenes
is accelerated by the presence of an sp2 nitrogen in an alcohol.
Scheme 1
(1) Kakiuchi, F.; Kan, S.; Igi, K.; Chatani, N.; Murai, S. J. Am. Chem.
Soc. 2003, 125, 1698.
(2) Chatani, N.; Ie, Y.; Kakiuchi, F.; Murai, S. J. Am. Chem. Soc. 1999,
121, 8645.
(3) Chatani, N.; Tatamidani, H.; Ie, Y.; Kakiuchi, F.; Murai, S. J. Am.
Chem. Soc. 2001, 123, 4849.
(4) Ishii, Y.; Chatani, N.; Yorimitsu, S.; Murai, S. Chem. Lett. 1998,
157.
(5) For a review on substrate-directed reactions, see: Hoveyda, A. H.;
Evans, D. A.; Fu, G. C. Chem. ReV. 1993, 93, 1307.
(6) For recent papers on chelation-assisted reactions, see: Jun, C.-H.;
Moon, C. W.; Hong, J.-B.; Lim, S.-G.; Chung, K.-Y.; Kim, Y.-H. Chem.
Eur. J. 2002, 485. Bendorf, H. D.; Colella, C. M.; Dixon, E. C.; Marchetti,
M.; Matukonis, A. N.; Musselman, J. D.; Tiley, T. A. Tetrahedron Lett.
2002, 43, 7031. Itami, K.; Mitsudo, K.; Yoshida, J. Angew. Chem., Int. Ed.
2002, 41, 3481. Ko, S.; Han, H.; Chang, S. Org. Lett. 2003, 5, 2687.
(7) For our recent paper on a chelation-assisted carbonylation at C-H
bonds, see: Asaumi, T.; Chatani, N.; Matsuo, T.; Kakiuchi, F.; Murai, S.
J. Org. Chem. 2003, 68, 7538.
The reaction of 1-hexene (6 mmol) and 2-pyridin-2-yl-
methanol (1) (2 mmol) in the presence of Rh4(CO)12 (0.04
mmol) in toluene (1 mL) at 100 °C under 3 atm of CO for
(8) For a review on hydroesterification, see: Colquhoun, H. M.;
Thompson, D. J.; Twigg, M. V. Carbonylation. Direct Synthesis of Carbonyl
Compounds; Plenum Press: New York, 1991. Ali, B. E.; Alper, H. In
Transition Metals for Organic Synthesis; Beller, M., Bolm, C., Eds.; Wiley-
VCH: Weinheim, 1998; pp 49-67. Kiss, G. Chem. ReV. 2001, 101, 3435.
10.1021/ol035582e CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/22/2003

20 h gave a 86:14 mixture of heptanoic acid pyridin-2-
ylmethyl ester (2n) and 2-methylhexanoic acid pyridin-2-
ylmethyl ester (2i) in total 87% isolated yield, along with a
trace amount of 2-ethylpentanoic acid pyridin-2-ylmethyl
ester (Scheme 2). Control experiments using benzyl alcohol,
Table 1. Hydroesterification of Alkenes Catalyzed by
Rh4(CO)12
a
Scheme 2
methanol, and pyridin-4-yl-methanol in place of 1 indicate
that the presence of the nitrogen at the 2-position in the
alcohol apparently accelerates the reaction.9 Higher CO
pressures (5 or 10 atm) have no effect on product yields (88%
and 83% GC yields, respectively). Ru3(CO)12 was, unexpect-
edly, not active under identical conditions,10 although it was
found to be active for carbonylation at C-H bonds in
N-heterocyclic compounds.7
To explore the scope and synthetic utility of this reaction,
a variety of alkenes were subjected to Rh-catalyzed hydro-
esterificaition (Table 1). The reaction of internal hexenes
gave a linear ester as the main product, along with branched
isomers. Higher temperatures slightly improved the linear
selectivity, indicating that a rapid isomerization occurred at
higher temperatures. The use of vinylcyclohexane and tert-
butylethylene gave the corresponding linear esters selectively.
The results of R-methylstyrene show that a higher CO
pressure is required for the reaction to proceed effectively
when the reaction is carried out at higher temperatures. This
is probably because higher CO pressures keep the catalyst
active at higher temperatures. Cyclic olefins also functioned
as an olefin partner. Some carbonyl functionalities, such as
ketones and esters, were tolerated under the reaction condi-
tions. The hydroesterification of ethylene (5 atm) proceeded
smoothly even at lower reaction temperatures (Scheme 3).
a Reaction conditions: alkene (6 mmol), 2-pyridylmethanol (2 mmol),
Rh4(CO)12 (0.04 mmol), in toluene (1 mL) under 3 atm of CO for 20 h.
b The ratio of linear (1-isomer) and branched isomer (2-isomer). c The ratio
of 1-, 2-, and 3-isomers. d Under CO (10 atm) for 40 h.
hydride mechanism.12 The coordination of sp2 nitrogen in 1
to a rhodium center followed by oxidative addition of an
O-H bond gives hydride-rhodium complex 3.13 The suc-
cessive insertion of an alkene and CO in 4 gives acyl-
Scheme 3
(9) The reaction of 1-hexene (6 mmol) with benzyl alcohol (2 mmol) in
the presence of Rh4(CO)12 (0.04 mmol) gave a trace amount of heptanoic
acid benzyl ester. When pyridine (2 mmol) was added, the benzyl ester
was formed in 13% yield (n:i ) 92:8). The use of 4-pyridylmethanol gave
the corresponding ester in 13% yield (n:i ) 95:5).
Two mechanisms have been proposed to date for the
hydroesterification of alkenes: a hydride mechanism and an
alkoxy mechanism.11 Although the mechanism of the present
hydroesterification of alkenes remains controversial, the
hydride mechanism is believed to be a true catalytic cycle.
A recent ab initio molecular orbital study also supports the
(10) When the reaction was carried out at 130 °C using Ru3(CO)12 as
the catalyst in place of Rh4(CO)12, 2 was obtained in 35% yield (n:i )
82:18).
(11) del Rio, I.; Claver, C.; van Leeuwen, P. W. N. M. Eur. J. Inorg.
Chem. 2001, 2719.
(12) Kawana, M.; Nakamura, S.; Watanabe, E.; Urata, H. J. Organomet.
Chem. 1997, 542, 185.
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Org. Lett., Vol. 5, No. 23, 2003

ring in an alcohol is demonstrated.14 We are currently
examining the catalytic use of pyridinemethanol in the
hydroesterification of alkenes with methanol or ethanol.
Other combinations of directing groups and catalysts are also
under investigation.
Scheme 4. Proposed Mechanism
Acknowledgment. This work was supported, in part, by
grants from Monbusho (The Ministry of Education, Science,
Sports, and Culture) and Japan Society for the Promotion of
Science. H.T. acknowledges Research Fellowships of J.S.P.S.
for Young Scientists. N.C. thanks the Tokuyama Foundation
and Nagase Science and Technology Foundation for financial
support.
Supporting Information Available: Experimental pro-
cedure and characterization data of all new products. This
material is available free of charge via the Internet at
http://pubs.acs.org.
rhodium complex 5. A carbon-oxygen bond-forming re-
ductive elimination would release the ester, regenerating the
catalyst.
In summary, the chelation-assisted hydroesterification of
alkenes, which is accelerated by the presence of a pyridine
OL035582E
(14) Chang recently reported on the chelation-assisted hydroesterification
of alkenes with 2-pyridylmethyl formate using Ru3(CO)12 as the catalyst.
No CO is required. Ko, S.; Na, Y.; Chang, S. J. Am. Chem. Soc. 2002,
124, 750.
(13) For a recent paper on the oxidative addition of alcohols with
transition metals, see: Blum, O.; Milstein, D. J. Am. Chem. Soc. 2002,
124, 11456 and references therein.
Org. Lett., Vol. 5, No. 23, 2003
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