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electrophiles to form furan-2(5H)-ones.18 However, 5-aryl-
substituted 2-siloxyfurans form 3-substituted 5-arylfuran-
2(3H)-ones exclusively as the thermodynamic product.
Compound 6a reacts with acetone and benzaldehyde at room
temperature in the presence of triethylamine to form 5-
Verlag GmbH & Co.; (c) X.-F. Wu, TraDnsOitI:io10n.1m03e9t/aCl8CcaCt0a5ly62ze3Dd
furan synthesis, 1st edition from Transition metal catalyzed
heterocycles synthesis series, 2015, Elsevier Publ.
3
For recent examples of transition metal-catalysed synthesis
of furans, see: (a) Y. Wu, Z. Huang, Y. Luo, D. Liu, Y. Deng, H.
Yi, J.-Fu. Lee, C.-W. Pao, J.-L. Chen and A. Lei, Org. Lett.,
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Org. Chem., 2017, 82, 4812; (c) K. B. Hamal and Wesley A.
Chalifoux, J. Org. Chem., 2017, 82, 12920; (d) R. Parnes, H.
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phenyl-(3-ylidene)furan-2(3H)-ones 8a,b in very high yields
(Scheme 3). The reaction of 6a with acetophenone required a
higher temperature to achieve a good yield of 5-phenyl-(3-
ylidene)furan-2(3H)-one 8c (82%) that was formed with
exclusive E-selectivity. Highly regioselective one-pot coupling-
hydrogenation of 6a was carried out using benzaldehyde and
triethylsilane. Upon reaction with benzylamine, furan 6a forms
ring opened product 10 in 96% yield. Reaction of 6a with
acrylonitrile or methyl acrylate formed Diels−Alder
cycloadducts and subsequent hydrolytic ring opening gave 11
and 12 as a mixture of diastereomers in moderate yields.
Nitriles 11a and 12a were stable at room temperature,
whereas esters 11b and 12b underwent loss of water and
quantitative aromatisation to form 2-substituted 4-
phenylphenol 13b, a compound that was previously accessible
only by cross-coupling reactions.19 Analogous 2-cyano-4-
phenylphenol 13a was obtained in 96% yield from a mixture of
11a and 12a by treatment with a catalytic amount of p-
toluenesulfonic acid (PTSA) at room temperature (Scheme 3).
In summary, we have discovered a new mechanistic
pathway for the formation of 2,5-disubstituted furans from
cycloprop-1-en-1-yl ketones generated from silyl-protected
enoldiazoketones. The regioselectivity of the process is totally
different from those formed from cycloprop-2-en-1-yl ketones.
The rearrangement is catalyst-dependent with rhodium(II)
carboxylates being the most efficient. DFT calculations have
been performed to understand the reaction mechanism,
showing that the electron-donating siloxy and aryl groups are
both essential to facilitate the reaction. Synthesized furans are
good sources of valuable furan-2(3H)-ones. Unlike the
reported unsubstituted 2-siloxyfurans or 5-alkyl-2-siloxyfurans,
our 5-aryl-2-siloxyfurans underwent coupling reactions with
electrophiles at position 3 selectively.
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We acknowledge U.S. National Science Foundation (CHE-
1212446) and the National Natural Science Foundation of
China (21232001) for supporting this research. The NMR
spectrometer used in this research was supported by a grant
from the U.S. National Science Foundation (1625963).
11 See the ESI
12 See the ESI
†
†
for the details on metal-catalyst screening.
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Conflicts of interest
There are no conflicts to declare.
15 For a related [1,5] sigmatropic alkyl shift, see: G.-Q. Chen, X.-
N. Zhang, Y. Wei, X.-Y. Tang and M. Shi, Angew. Chem., Int.
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