Journal of the American Chemical Society
Communication
Table 3. Ni-Catalyzed Carboxylation of Alkyl Sulfonates ,
ab
starting materials, and ease of execution without the need for air-
or moisture-sensitive materials. Further investigations into the
mechanism and the extension to more challenging substrate
combinations are currently underway.
ASSOCIATED CONTENT
Supporting Information
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*
S
AUTHOR INFORMATION
a
Reaction conditions: 3a−f (0.25 mmol), NiBr ·glyme (10 mol %),
2
L14 (26 mol %), and Mn (2.4 equiv) in DMF (0.25 M) at 50 °C for
1
shown. At 60 °C. At 100 °C. NiBr ·glyme (7.5 mol %). At 70 °C.
Notes
b
2 h. Isolated yields (averages of at least two independent runs) are
The authors declare no competing financial interest.
c
d
e
f
2
ACKNOWLEDGMENTS
■
presence of other C−O electrophiles such as alkyl pivalates did
not interfere, resulting in the selective carboxylation of the alkyl
sulfonate backbone (3f). Overall, we believe that the results in
Tables 2 and 3 show the robustness and the prospective impact
of our Ni-catalyzed carboxylative protocol when employing
This paper is dedicated to the memory of Prof. Gregory L.
Hillhouse. We thank ICIQ, the European Research Council
ERC-277883), and MINECO (CTQ2012-34054 and Severo
Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319) for
support. Johnson Matthey, Umicore, and Nippon Chemical
Industrial are acknowledged for gifts of metal and ligand sources.
Y.L. and J.C thank COFUND and the European Union for a
Marie Curie Fellowship (FP7-PEOPLE-2012-IEF-328381).
(
23
unactivated alkyl bromides or alkyl sulfonates.
Although an in-depth mechanistic study should await further
investigations, we wondered whether the reaction was initiated
by β-hydride elimination followed by a hydrocarboxylation
2
4
event. Thus, we subjected 5-phenylpentene (5) to our
REFERENCES
optimized conditions. Under the limits of detection, we did
■
12
not detect any carboxylation reaction. A similar result was
obtained when n-butylmanganese bromide (6) was exposed to
our Ni/L16 system in the presence or absence of Mn, thus
leaving some doubt about the intermediacy of organomanganese
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1
2
species. In order to shed light on the mechanism, we decided to
12
study the carboxylation reaction of 7a and 7b (Scheme 3).
(
1
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Scheme 3. Mechanistic Experiments
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(
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1
1
(
́
2
(
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Diastereomerically pure 8 was anticipated for a mechanism
25
consisting of a “classical” oxidative addition; on the contrary, a
statistical mixture of diastereoisomers in 8 would indicate a free-
radical mechanism via single-electron transfer (SET). As shown
(8) For a review, see: Correa, A.; Martin, R. Angew. Chem., Int. Ed.
2
009, 48, 6201.
1
in Scheme 3, H NMR spectroscopic analysis of the crude
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26
mixture revealed the loss of stereochemical integrity at C1.
Similar behavior was found for 7c and 7d, an observation that
1
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might indicate a scenario consisting of SET processes via Ni(I)
2
7−31
species.
In line with this notion, we observed that radical
(
clocks such as (bromomethyl)cyclopropane and 1-bromo-5-
hexene resulted in ring-opened products.
In summary, we have reported a new catalytic carboxylation of
unactivated primary alkyl bromides and sulfonates possessing β-
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(
2
hydrogens with CO that gives access to valuable carboxylic
2
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Tatsumi, M.; Ogawa, A. Tetrahedron Lett. 2010, 51, 6580.
(12) See the Supporting Information for details.
acids. This method is characterized by its exquisite functional
group compatibility, mild conditions, ready availability of the
C
dx.doi.org/10.1021/ja5064586 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX