Organic Letters
Letter
opened products 5n and 6n, respectively. Neither 2n nor 6n was
obtained, but 5n (gray box) was isolated in 54% yield. The
formation of 5n can be rationalized by a switch from an ionic in
the first to a radical mechanism in the second C(sp3)−Si
coupling. In other words, α-bromo-substituted alkyl bromide 1n
reacts through the ionic pathway14 and the intermediate α-
silylated alkyl bromide couples through the radical pathway.13a
To further verify this, we independently prepared the α-silylated
bromide 7a and subjected it to the standard protocol to afford
the cross-coupling product 2a in 31% GLC yield (Scheme 4,
bottom).
AUTHOR INFORMATION
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Corresponding Author
ORCID
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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On the basis of this insight as well as our previous quantum-
chemical analysis of the radical process,13a we suggest the
following catalytic cycle for the double C(sp3)−Si cross-
coupling reaction of geminal dibromides (1 → 2, Scheme 5).
This research was supported by the Alexander von Humboldt
Foundation (Georg Forster Research Fellowship to H.H.,
2016−2018) and the Deutsche Forschungsgemeinschaft (Oe
249/15-1). M.O. is indebted to the Einstein Foundation Berlin
for an endowed professorship.
Scheme 5. Proposed Catalytic Cycle
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ASSOCIATED CONTENT
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(16) Hazra, C. K.; Fopp, C.; Oestreich, M. Chem. - Asian J. 2014, 9,
3005−3010.
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* Supporting Information
(17) (a) Bausch, M. J.; Gong, Y. J. Am. Chem. Soc. 1994, 116, 5963−
5964. See also: (b) Wilt, J. W.; Belmonte, F. G.; Zieske, P. A. J. Am.
Chem. Soc. 1983, 105, 5665−5675 and cited references.
The Supporting Information is available free of charge on the
General procedures, experimental details, and character-
ization/spectral data for all new compounds (PDF)
C
Org. Lett. XXXX, XXX, XXX−XXX