Organic Letters
Letter
and an nBuLi/D2O route for the regioselective deuterohy-
drogenation and hydrodeuterogenation of 1,1-diaryl alkenes.
We applied the less active BF3·Et2O instead of B(C6F5)3 as the
catalyst for economic reasons and the much easier handling to
achieve similar good results without utilizing a glovebox for the
regiodivergent addition of HD/DH to alkenes.
Scheme 9. Hydrodeuterogenation of Alkenes of Type 7 with
4 as the HD Source
ASSOCIATED CONTENT
* Supporting Information
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The Supporting Information is available free of charge at
Synthesis, analytical data, and NMR spectra (PDF)
AUTHOR INFORMATION
Corresponding Author
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Gerhard Hilt − Institut fur Chemie, Universitat Oldenburg D-
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798 3329
Author
Luomo Li − Institut fur Chemie, Universitat Oldenburg D-
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26111 Oldenburg, Germany
Complete contact information is available at:
The reactions were performed with two samples of the HD
surrogate that were obtained by the nBuLi/D2O route (sample
A) as well as with the surrogate obtained from the Diels−Alder
route with the deuterated 1,3-diene (route B). Generally, the
products generated by route A gave the higher level of
incorporation of deuterium while the yields are higher when
route B was realized. The rationale for this difference is the
higher deuterium content of 4 when route A was utilized, and
the decreased yield might be caused by unknown impurities in
these samples of 4.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The financial support by the German science foundation
(DFG) is gratefully acknowledged (Hi655-GRK 2226).
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REFERENCES
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Nevertheless, these results underline the mechanism
proposed by Oestreich in which two parallel reaction pathways
led to the desired deuterated products. After abstraction of a
hydride anion from 3 (and a deuteride anion from 4), the
corresponding Wheland complexes 11 and 12 are formed
(Scheme 8). These complexes represent strong Brønsted acids
and protonate the starting material 7 to generate the more
stable carbenium ions that react with either the corresponding
dihydroaromatic compounds 11 and 12 or the reducing agents
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̈
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H and DBF4 to close the catalytic cycle.
The new HD/DH surrogates 3 and 4 have some interesting
features compared to those introduced by Oestreich. The
phenyl group on the diene has two major positive effects. For
one, the 1,3-diene 6 is much easier to handle than alkyl-
substituted 1,3-diene (e.g., octa-1,3-diene), as these simple
dienes are much more volatile. Second, the phenyl group
stabilizes the carbenium ions of the Wheland complexes 11
and 12 significantly so that the deuteride and hydride ions are
abstracted by BF3, respectively, in the initiation step of the
reaction sequence. The stabilization of the Wheland complexes
11 and 12 by the phenyl group obviously overrules a possible
stabilization of the trimethylsilyl group via the β-silyl effect.
The positive charge in 11 and 12 is not located at the β-
positions so that the β-silyl effect is not operative, but this does
not include the possibility that the carbenium ion is
destabilized by the trimethylsilyl group.
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In conclusion, we developed dihydroaromatic DH (3) and
HD (4) surrogates via cobalt-catalyzed Diels−Alder reactions
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D
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