10.1002/adsc.201900276
Advanced Synthesis & Catalysis
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or 1k with sulfoxonium ylides 2b, or 2e finished
under the above standard conditions, it was found that
a successive dehydration for an intramolecular
cyclization could be performed smoothly at the same
temperature by adding aqueous sulfuric acid,
affording corresponding flavonoids 4a-e in
satisfactory yields respectively (Scheme 6).
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Scheme 6. Aldehydic C–H Functionalization Followed by
Dehydrative Cyclization for the Synthesis of Flavonoids in
One-pot.
In conclusion, we have developed an aldehydic C-
H functionalization reaction of salicylaldehydes 1
with sulfoxonium ylides 2 by rhodium(III) catalysis
and in the presence of sodium acetate. It was found
that various functional groups in salicylaldehydes 1
and sulfoxonium ylides 2 are compatible with the
reaction, affording corresponding coupling products 3
in moderate to good yields. A plausible mechanism
involving aldehydic C(sp2)-H activation by
rhodium(III) and rhodium(III)-catalyzed carbene
insertion
is
also
proposed.
Moreover,
salicylaldehydes 1 and sulfoxonium ylides 2 were
able to undergo the C-H functionalization followed
by dehydrative cyclization in one-pot to produce
corresponding flavonoids 4.
Experimental Section
General procedure for the aldehydic C-H functionalization
reaction: The reaction mixture of salicylaldehyde 1 (0.10
mmol), sulfoxonium ylide 2 (0.12 mmol), [Cp*RhCl2]2
(1.5 mg, 0.0025 mmol, 2.5 mol %) and NaOAc (16.4 mg,
0.20 mmol) in DCE (2.0 mL) was stirred at 90 °C for 24 h.
Then, the mixture was evaporated under reduced pressure,
and the residue was purified by column chromatography
(silica gel, ethyl acetate/ petroleum ether = 1/20 as eluent)
to give desired coupling product 3.
[4] Some papers on aldehydic C-H functionalizations: a)
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Acknowledgements
[5] a) P. S. Sun, S. Gao, C. Yang, S. Guo, A. Lin, H. Yao,
Org. Lett. 2016, 18, 646 4-6467; b) G.-D. Xu, Z.-Z.
Huang, New J. Chem. 2018, 42, 18358-18362.
The financial support from National Natural Science Foundation
of China (No. 21372195) is gratefully acknowledged.
References
[1] Some reviews on C-H functionalizations by metal
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4
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