European Journal of Organic Chemistry
10.1002/ejoc.201601230
FULL PAPER
[1]
[2]
[3]
For selected reviews on transition metal catalyzed allylic substitution,
see: a) B. M. Trost, D. L. Van Vranken, Chem. Rev. 1996, 96, 395-422.
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Conclusions
To conclude, starting from simple readily available alkynes and
1,3-dicarbonyl compounds, e.g. β-keto esters, β-keto amides
and 1,3-diketones, we have developed a highly regioselective
rhodium-catalyzed C-C bond forming reaction furnishing
valuable branched α-allylated 1,3-dicarbonyl compounds in good
to excellent yields. The utility of the obtained products was
demonstrated through one-step transformations to pyrazolones,
oxazoles and pyrazoles, which are privileged medicinal scaffolds
of interest. Furthermore, simple basic saponification followed by
decarboxylation provided γ,δ-unsaturated ketones, products of a
formal methyl-ketone-enolate allylation or a Claisen/Carroll-type
rearrangement. Further attempts regarding extension of this
method to the formation of quaternary centers, other (carbon-)
nucleophiles as well as the development of an asymmetric
catalytic variant are ongoing in our laboratories.
For selected examples on Pd catalyzed allylic alkylation to achieve
branched products, see: a) B. M. Trost, S. Malhotra, W. H. Chan, J. Am.
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Experimental Section
[4]
For selected examples on Rh catalyzed allylic alkylation to achieve
branched products, see: a) J. Tsuji, I. Minami, I. Shimizu, Tetrahedron
Lett. 1984, 25, 5157-5160. b) T. Hayashi, A. Okada, T. Suzuka, M.
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General procedure A for the addition of a 1,3-dicarbonyl compound
to a terminal alkyne
A flame-dried 10 ml Young tube was charged with [Rh(COD)Cl]2 (4.9 mg,
10 μmol, 2.0 mol %) and DPEphos (16.2 mg, 30 μmol, 6.0 mol %). The
tube was evacuated and backfilled with argon, before pre-mixed solvent
of DCE and EtOH (5:1, 1.25 ml) was added. Then the alkyne (0.75 mmol,
1.5 eq.), TFA (8.0 μl, 12 mg, 0.1 mmol, 20 mol %), and the 1,3-dicarbonyl
compound (0.5 mmol. 1.0 eq.) were added. The tube was sealed and
heated to 80 °C for 16 hours. The solvent was removed under reduced
pressure and the crude product was purified by flash chromatography on
silica gel.
[5]
For selected examples on other metal catalyzed allylic alkylation to
achieve branched products, see: a) For Fe: B. Plietker, Angew. Chem.
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B. Trost, Science 1991, 254, 1471-1477.
General procedure B for the addition of a 1,3-dicarbonyl compound
to a terminal alkyne
A flame-dried 10 ml Young tube was charged with [Rh(COD)Cl]2 (6.2 mg,
12.5 μmol, 2.5 mol %), DPEphos (20.2 mg, 37.5 μmol, 7.5 mol %) and p-
CF3C6H4COOH (47.5 mg, 0.25 mmol, 50 mol %). The tube was
evacuated and backfilled with argon, before pre-mixed solvent of DCE
and EtOH (5:1, 1.25 ml) was added. Then the alkyne (1.0 mmol, 2.0 eq.)
and the 1,3-dicarbonyl compound (0.5 mmol. 1.0 eq.) were added. The
tube was sealed and heated to 80 °C for 16 hours. The solvent was
removed under reduced pressure and the crude product was purified by
flash chromatography on silica gel.
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Acknowledgements
This work was supported by the DFG and the Fond of the
Chemical Industry. We thank Umicore, BASF and Wacker for
generous gifts of chemicals. Anne Aßmann (University Freiburg)
is acknowledged for her motivated and skillful technical
assistance.
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a) B. M. Trost, W. Brieden, K. H. Baringhaus, Angew. Chem. 1992, 104,
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Keywords: rhodium • 1,3-dicarbonyl compounds • alkynes •
regioselective addition • γ,δ-unsaturated ketones
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