RSC Advances
Communication
and A. G. H. Wee, Org. Lett., 2000, 2, 1777–1779; (b)
J. H. Hansen, B. T. Parr, P. Pelphrey, Q. Jin, J. Autschbach
and H. M. L. Davies, Angew. Chem., Int. Ed., 2011, 50,
2544–2548.
Conclusions
Domino azide-metallocarbene coupling/nucleophilic addition
has been achieved, forming substituted indolone systems by
sequential formation of adjacent C–N and C–C bonds. With
unsubstituted diazoketone precursors, rapid autoxidation
occurs aer nucleophilic trapping. A variety of nucleophiles can
be used, including active methylenes, silyl ketene acetals,
Danishefsky's diene, or N-methylindole. Use of 2-azido- or 2-
aminobenzoyl chloride allows for 1-step construction of the
natural product tryptanthrin. Doubly stabilized diazoketones
also undergo efficient cyclization and nucleophilic capture,
generating a variety of ester-substituted indolinones. Variation
of ring substitution had no observable effect on the efficiency of
the process. Further studies of this process will be reported in
due course.
11 Notably, Driver has recently shown that o-styryl azides
undergo rhodium catalyzed indole formation via apparent
nitrene intermediates: C. Jones, Q. Nguyen and
T. G. Driver, Angew. Chem., Int. Ed., 2014, 53, 785–788.
12 Both azides and diazo groups are potentially explosive, and it
is recommended that the (C + O)/N ratio be $3 to ensure
against unanticipated detonation of azide-containing
¨
compounds: T. Keicher and S. Lobbecke, in Organic Azides:
¨
Syntheses and Applications, ed. S. Brase and K. Banert,
Wiley, Chichester, 2010, pp. 3–27.
13 Because the (C + O)/N ratio for 6a is below 3, we limited the
scale of its preparation to no more than 1 g, and individual
reactions using 6 were generally run at a scale of 50–100 mg.
When stored under argon at –20 ꢀC in a foil-wrapped
container, 6a was found to be stable for at least 2 weeks.
Compounds 6b–e appear to lack any special sensitivity,
and are amenable to use in gram-scale reactions.
Acknowledgements
We thank NSERC for support of this work, and the University of
Alberta for a Queen Elizabeth II Graduate Scholarship (TMB).
14 (a) Isolation of compound 4a from a mushroom pigment:
S. Takekuma, H. Takekuma, Y. Matsubara, K. Inaba and
Z. Yoshida, J. Am. Chem. Soc., 1994, 116, 8849–8850; (b)
Formation of 4a from microwave-assisted cyclization of an
O-phenyloxime: F. Portela-Cubillo, J. S. Scott and
J. C. Walton, Chem. Commun., 2007, 4041–4043.
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31958 | RSC Adv., 2014, 4, 31955–31959
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