D. L. Priebbenow, L.-H. Zou, P. Becker, C. Bolm
SHORT COMMUNICATION
Supporting Information (see footnote on the first page of this arti-
cle): Detailed description of the experimental procedures and ana-
lytical data for all compounds.
acid in the presence of furan, the cycloaddition proceeds
rapidly to afford bicyclo[3.2.1]octene 31 in excellent yield
with a high level of diastereoselectivity (Scheme 6).[14] If the
enol acetal contains an ester substituent, as in our case,
activation of acetal 12 in the presence of furan leads to δ,δ-
bis(furan-2-yl) β-keto ester 13 as the sole product through
disubstitution in excellent yield. In an analogous example,
Hsung and co-workers observed that the use of a chiral
aminal instead of the acetal moiety led to the formation of
a 1:1 mixture of cycloaddition product 33 and monoaddi-
tion product 34 (dr ≈ 9:1 for both products in the presence
of the chiral auxiliary).[19] As such, to allow further devel-
opments to be made in the asymmetric [4+3] cycloaddition
reaction, the electronic environment and stability of the req-
uisite oxyallyl cationic species is an important consider-
ation.
Acknowledgments
In part, this research was supported by the Cluster of Excellence
(Tailor-Made Fuels from Biomass) funded by the Excellence Initia-
tive of the German Federal and State Governments. The authors
acknowledge the Alexander von Humboldt Foundation for a post-
doctoral fellowship to D. L. P. and the Chinese Scholarship Coun-
cil (CSC) for a predoctoral stipend to L. H. Z.
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Scheme 6. Subtle electronic differences in the enol substrate affect
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Conclusions
In summary, an efficient catalytic protocol for the prepa-
ration of δ,δ-bis(aryl) β-keto esters has been developed in-
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als. This method proceeded well with a range of aromatic
nucleophiles to afford a valuable series of functionalised β-
keto esters, which are readily amenable to further derivatis-
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Experimental Section
General Procedure for the Acetal Disubstitution Reaction: To an
oven-dried Schlenk tube under an atmosphere of argon was added
enol acetal 12 (73 mg, 0.25 mmol), the aromatic nucleophile
(0.75 mmol) and CH2Cl2 (3 mL). After cooling of this solution to
–78 °C, a few drops of TMSOTf were added. The reaction mixture
was stirred at this temperature for 2 h and then warmed to room
temperature and stirred for an additional 14 h. After this time, the
solvent was evaporated, and the product was purified by column
chromatography (pentane/ethyl acetate) to afford the bis(aryl) β-
keto ester product.
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