10.1002/anie.202006542
Angewandte Chemie International Edition
RESEARCH ARTICLE
reactions of 2-halophenols with terminal alkynes.[22] By employing
our diazo quinone and boronic ester coupling reaction as a key
step, we developed a transition-metal-free synthetic route to this
class of compounds. As shown in Scheme 7, the reaction of diazo
quinone 1j with boronic ester 13 gave coupling product 14a in
80% yield, which then underwent I2-catalyzed cyclization and
BBr3-mediated demethylation, giving naturally occurring
benzo[b]furan moracin M in an overall yield of 63% for three steps.
Likewise, stemofuran A was prepared with a similar efficiency.
tolerant of various functional groups, including C(sp2)-halides (F,
Cl, Br, and I), esters, alkenes, amines, ethers, cyano groups and
heteroaromatics. The cross-coupling reaction has been
successfully used in the short synthesis of multi-substituted
triphenylenes and three natural products, honokiol, moracin M
and stemofuran A. Mechanistic studies and density functional
theory (DFT) calculations revealed that the reaction involves
attack of a boronic ester by a singlet quinone carbene followed by
a 1,2-rearrangement via a stepwise mechanism.
Acknowledgments
This work was supported by the National Natural Science Foundation of
China(NSFC21472159), Hong Kong ResearchGrants Council General
Research Fund (17306714, 17303815, and 17301817), and Basic
Research Program-Shenzhen Fund(JCYJ20170412140251576).
Keywords: diazo compounds • boronic esters • transition-metal-
free reaction • C(sp2)-C(sp2) bond • cross-coupling reaction
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Scheme 5. Synthesis of multi-substituted triphenylenes.
Scheme 6. Synthesis of honokiol.
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Scheme 7. Synthesis of stemofuran A and moracin M.
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Conclusion
In summary, we have developed a transition-metal-free C(sp2)-
C(sp2) bond forming reaction via the cross-coupling of diazo
quinones with catechol boronic esters. The reaction provides
efficient access to a variety of biaryls and alkenyl phenols in good
to high yields under mild conditions and is applicable to the
derivatization of bioactive organic compounds. The reaction is
6
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