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Issue 28, 2015
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Rhodium(iii)-catalyzed cascade oxidative annulation reactions of aryl imidazolium salts with alkynes involving multiple C–H bond activation

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Abstract

The cascade oxidative annulation reactions of aryl imidazolium salts with alkynes proceed efficiently in the presence of [Cp*RhCl2]2 and Cu(OAc)2·H2O to give substituted imidazo[1,2-a]-quinolinium salts and benzo[ij]imidazo[2,1,5-de]quinolizinium salts. The reactions were through the normal and abnormal N-heterocyclic carbene (NHC)-directed cyclometalation, alkyne insertion into the Rh–C bond, and reductive elimination of alkenyl and NHC ligands. The reactions are highly regioselective with unsymmetrical alkynes and can be achieved stepwise by controlling the reaction conditions. This provides a new application of NHCs as directing groups and substrates in the synthesis of fused N-heterocyclic compounds. The N-substituting group of the benzo[ij]imidazo[2,1,5-de]quinolizinium salts could be removed successfully with pyridine to afford benzo[ij]imidazo[2,1,5-de]quinolizines in excellent yields. Moreover, some of the benzo[ij]imidazo[2,1,5-de]quinolizinium salts exhibit intense fluorescence which might be useful in organic electronic materials.

Graphical abstract: Rhodium(iii)-catalyzed cascade oxidative annulation reactions of aryl imidazolium salts with alkynes involving multiple C–H bond activation

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Supplementary files

Article information


Submitted
24 Apr 2015
Accepted
04 Jun 2015
First published
05 Jun 2015

Org. Biomol. Chem., 2015,13, 7695-7710
Article type
Paper
Author version available

Rhodium(III)-catalyzed cascade oxidative annulation reactions of aryl imidazolium salts with alkynes involving multiple C–H bond activation

Q. Ge, B. Li, H. Song and B. Wang, Org. Biomol. Chem., 2015, 13, 7695
DOI: 10.1039/C5OB00823A

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