C O MMU N I C A T I O N S
Table 2. Hydroesterification of Various Alkenes with 1ba
hydroesterification reaction of alkenes guided by a chelation-assisted
strategy for the first time. Using 2-pyridylmethyl formate 1b,
decarbonylation could be almost completely suppressed with a Ru
catalyst during the reaction course, allowing one-carbon elongated
esters starting from alkenes in high yield and excellent selectivity
without requirement of high pressure CO. This result should
immediately pave more opportunities for searches of efficient and
selective new C-C forming catalytic reactions by means of the
chelation strategies.
Acknowledgment. This research was financially supported by
the CMDS at KAIST. This paper is dedicated to Professor Robert
H. Grubbs on the occasion of his 60th birthday.
Supporting Information Available: Spectral data and copies of
1H and 13C NMR spectra for new compounds (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
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determined by H NMR of the crude reaction mixture.
1
c
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1
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(
10) Although a partial decomposition of DMF by Ru complexes has been
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ylation of DMF was not observed under the present conditions.
ized. However, on the basis of accumulating reports that low-valent
Ru complexes, especially Ru
3
(CO)12, show high catalytic activity
(11) Tetrasubstituted alkenes were not reactive under these conditions.
(12) Determined by comparison with known data (ref 5d) after conversion of
15a
for the activation of the formyl C-H bond such as of formamides,
the 2-pyridylmethyl ester to the corresponding benzyl ester.
alkyl formats,1 or aldehydes, we propose a plausible mechanism
in Scheme 1. Although whether ruthenium acts as a mononuclear
or as a cluster is not clear at the present time, coordination of the
ruthenium to pyridyl nitrogen should facilitate activation of the
formyl C-H bond,16 leading to a six-membered chelation inter-
mediate. We believe that such a chelation subsequently results in
effective suppression of the decarbonylation route.17 To demonstrate
the applicability of the present process, reactions under solvent-
free conditions were next tried. The neat reaction of 3,3-dimethyl-
5b
15c
(13) Reaction of n-butyl vinyl ether with 1b also resulted in exclusive formation
of a corresponding R-adduct in 64% isolated yield in 1,2-dichloroethane
3
(12 h, 135 °C) with Ru (CO)12 (5 mol %).
(14) (a) Suggs, J. W. J. Am. Chem. Soc. 1978, 100, 640. (b) Bianchini, C.;
Meli, A.; Peruzzini, M.; Vacca, A.; Zanobini, F. Organometallics 1987,
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Organomet. Chem. 1987, 331, 379. (b) Kondo, T.; Okada, T.; Mitsudo,
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Y.; Watanabe, Y. J. Org. Chem. 1990, 55, 1286.
1
(
16) A putative ruthenium hydrido peak was observed on H NMR at -18
3 6 6
ppm upon heating of 1b with Ru (CO)12 (0.5 equiv) in C D at 135 °C.
(
17) Murai et al. have recently reported a chelation-assisted reductive decar-
boxylation reaction, in which the C-O bond of 2-pyridylmethyl esters is
converted to hydrocarbons, see: Chatani, N.; Tatamidani, H.; Ie, Y.;
Kakiuchi, F.; Murai, S. J. Am. Chem. Soc. 2001, 123, 4849.
1
-butene (5 equiv) with 1b (1 equiv) proceeded with impressive
efficiency, affording exclusively a linear ester in 89% isolated yield
using only 0.2 mol % Ru (CO)12 catalyst (135 °C, 5 h). The
(18) See Supporting Information for details.
3
(
19) The products were quantitatively isolated by a simple acid-base extraction
according to the phase-tag procedure as described in ref 8d, thus the
recovered Ru complex exhibited significantly diminished catalytic activity
as compared to that of the fresh one.
produced 2-pyridylmethyl esters could be readily hydrolyzed under
mild conditions,18 quantitatively providing the parent carboxylic
acids with complete recovery of 2-pyridinemethanol.19
In summary, we have developed a practical useful catalytic
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