3
With the optimized conditions, a series of alkenes were
reacted with the 2-oxo-2-phenylacetic acid (1a) under the
optimized conditions, respectively (Scheme 2). The
corresponding products (3a-3g) were obtained in moderate to
good yields. Alkyl or halogen substituted styrenes can be
tolerated well. Different α-keto acids were also tested (3h-3u)
with various alkenes, and they were all well sustained. Methoxyl
group on aryl rings of the α-keto acids may slightly affect the
transformation, giving product 3k and 3l in comparatively low
yields. But it is glad to see that alkene with fused-ring like 2-
vinylnaphthalene was also sustained in this transformation,
giving the desired product 3t in moderate yield. And α-keto acid
of heterocyclic derivative as the 2-oxo-2-(thiophen-2-yl)acetic
acid can give the coupling product 3u, either. These results
reflected a wide tolerability of this catalytic process.
3. Conclusion
In summary, a decarboxylative cross-coupling process of α-
keto acids with alkenes is reported. The approach, with the easily
available starting materials, using silver carbonate as a catalyst
and K2S2O8 as an oxidant, provides a novel methodology to get
the chalcone derivatives in moderate to high yields. Preliminary
results of mechanism experiments indicated that a free-radical
process may be involved in this transformation. Further
investigations upon the mechanism studies as well as the
expansion of the substrate scope are currently undergoing in our
group.
Acknowledgments
We gratefully acknowledge the Fundamental Research Funds
for the Central Universities (31920160010)..
2.3. Mechanism studies
In order to have an insight of the mechanism of this
decarboxylative cross-coupling process, the reactions were
operated with radical inhibitors (see the Supporting information).
When 3 equiv. of TEMPO (2,2,6,6-tetramethylpiperidinooxy) or
BHT (2,6-di-tert-butyl-4-methylphenol) were added into the
reactions of 1a with 2a under the standard condition, it was
observed that the reactions were totally inhibited (Scheme 3).
And when BHT was used, an adduct of BHT with acyl radical
was isolated and determined by NMR and MS. These results
suggest that a radical process may be involved. And with the
previous literatures5e, 6, a proposed mechanism of this reaction is
illustrated in scheme 4.
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