Angewandte Chemie International Edition
10.1002/anie.201806237
COMMUNICATION
detected at all after acidic workup. In addition, the β-elimination
proceeds as syn-elimination bridged by KOtBu, which would be
the origin of the complete E-selectivity of the product.
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Finally we conducted transformations of silylation product
a to prove the synthetic utility of our silylation. Cross-couplings
of 3a with iodoarenes by using SingaCycle-A1[16] as a palladium
catalyst in the presence of tetrabutylammonium fluoride took
place in excellent yields (Scheme 6a). The cross-coupling could
employ a substrate with an ester moiety which could not endure
under Wenkert’s conditions.[1a] According to Kishi’s procedure,[17]
Compound 3a was also converted to the corresponding (E)-
iodoalkene 5 protected by a silyl group on the phenol moiety
Scheme 6b).
3
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[
Scheme 6. Transformations of 3a. IPr = 1,3-Bis(2,6-diisopropylphenyl)imidazol-
1
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In conclusion, we have established catalytic ring-opening
silylation of benzofurans by employing a combination of a copper
catalysis and 1,2-di-tert-butoxy-1,1,2,2-tetramethyldisilane (2a),
which was easily prepared and significantly effective for this
silylation. DFT calculations provided insight into the reaction
mechanism and stereoselectivity of this silylation. In addition,
transformations of the silylated product was demonstrated to
prove the products to be nice building blocks in organic synthesis.
[
8]
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[
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Acknowledgements
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10] K. Kubota, K. Hayama, H. Iwamoto, H. Ito, Angew. Chem. 2015, 127,
933; Angew. Chem. Int. Ed. 2015, 54, 8809.
8
This work was supported by JSPS KAKENHI Grant Numbers
JP18H04254, JP16H01019, JP16H04109, and JP16H06887.
H.Y. thanks The Asahi Glass Foundation for financial support.
H.S. acknowledges JSPS Predoctoral Fellowship.
[
11] For M06 functional: a) Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008,
120, 215; b) Y. Zhao, D. G. Truhlar, Acc. Chem. Res. 2008, 41, 157.
[12] For SMD method: A. V. Marenich, C. J. Cramer, D. G. Truhlar, J. Phys.
Chem. B 2009, 113, 6378.
[
13] Although optimization of the structure of INT4 was almost completed, the
flexibility of the coordinating THF disturbed convergence despite many
attempts.
Conflict of interest
[14] DFT calculations were performed with Gaussian 09 program and Firefly
version 8. For details, see Supporting Information.
[
15] Since there are too many possible structures of silylcopper precursors to
determine ΔG between 1a and INT1, an energy diagram after
complexation of 1a with a silylcopper species is shown in Scheme 5.
16] E. A. B. Kantchev, J. Y. Ying, Organometallics 2009, 28, 289.
17] D. P. Stamos, A. G. Taylor, Y. Kishi, Tetrahedron Lett. 1996, 37, 8647.
The authors declare no conflict of interest
Keywords: Benzofurans • Copper catalyst • DFT calculations •
Disilane • Silylation
[
[
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