Organic Letters
Letter
phenylpropionaldehyde 1t was examined, and homoallylic
alcohol 3ta′ was obtained in 92% yield as a 1:1 diastereomeric
mixture. This result indicated that the allylation proceeded via
an acyclic transition state for the addition of the allylsilane to
the carbonyl carbon of the aldehyde and not via a chairlike six-
membered transition state (the Zimmerman−Traxler model).
In order to elucidate the reaction mechanism, we examined the
allylation with allylsilane 2d possessing a sterically hindered
TBDMS group. The reaction did not afford the allylation
product 3aa′. This result, along with the reaction scope
provided in Table 1, clearly suggested that the plausible rate-
determining step in the catalytic cycle is silyl group migration
and not addition of the allylsilane to the aldehyde carbonyl
carbon or dissociation to regenerate the initial active Lewis
acid cobalt porphyrin complex.
In conclusion, we have demonstrated for the first time that a
cobalt porphyrin Lewis acid can catalyze the allylation of
aldehydes with allyltrimethylsilanes. The use of a cationic
cobalt porphyrin complex as the Lewis acid catalyst facilitates
activation of the aldehyde via coordination and dissociation of
the product, so that the reaction can proceed to completion
within a short time under mild conditions. The allylation
proceeds with 1 mol % of the cobalt porphyrin catalyst CP1 at
25 °C within 1 h. The coordination of the aldehyde to the
cobalt porphyrin catalyst is demonstrated by Co K-edge XAS
analysis and DFT calculations. Moreover, allylation with a
diverse range of aldehydes can be promoted by the readily
available [Co(TPP)]SbF6. Since the use of a metalloporphyrin
Lewis acid as the catalyst enables allylation within a short time,
further research into metalloporphyrin Lewis acid catalysts may
reveal the intrinsic catalytic activity of first-row transition
metals. Studies in this regard are ongoing in our laboratory,
and the results will be reported in due course.
Prof. Tsunehiro Tanaka (Kyoto University), Prof. Masaharu
Nakamura (Kyoto University), Prof. Hikaru Takaya (Kyoto
University), Dr. Tetsuo Honma (Japan Synchrotron Radiation
Research Institute; JASRI), Dr. Hironori Ofuchi (JASRI), Dr.
Masafumi Takagaki (JASRI), and Mr. Kyohei Fujiwara
(Ajinomoto Co., Inc.) for valuable support in the X-ray
absorption fine structure analysis. Part of this study was
performed at the beamline of the SPring-8 synchrotron
radiation facility (Proposal Nos. 2016A1549 and 2019A1712).
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
Experimental procedures including spectroscopic and
analytical data of new compounds (PDF)
AUTHOR INFORMATION
Corresponding Authors
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(4) Ishihara, K.; Hiraiwa, Y.; Yamamoto, H. Synlett 2001, 30, 1851.
ORCID
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by Advanced Catalytic Trans-
formation Program for Carbon Utilization (ACT-C No.
JPMJCR12YE) from Japan Science and Technology Agency
(JST) and a Grant-in-Aid for Scientific Research (18H04253,
17KT0006, and 15H05845) from the Ministry of Education,
Culture, Sports, Science and Technology (Japan). T.K.
acknowledges the Asahi Glass Foundation. We are grateful to
D
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