Aldehyde as a Traceless Directing Group for Rh(III)-Catalyzed C–H Activation: A Facile Access to Diverse Indolo[1,2-a]quinolines
摘要:
The aldehyde group has been developed for the first time as a traceless directing group to promote regioselective Rh(III)-catalyzed C-H activation/cyclization of indolyl aldehydes with alkynes. This protocol streamlines access to a variety of appealing indolo[1,2-a]quinoline structures. As illustrative examples, a concise three-step synthesis of indolo[1,2-a]quinoline-based sensitizers is accomplished that exhibits the potential of C-H activation in the construction of organic optoelectronic materials.
The rhodium(III)-catalyzed direct alkenylation of N-phenylindole-3-carboxylic acids with alkenes including acrylate ester, acrylamide, and acrylonitrile proceeds smoothly at the C4-position through regioselective C–H bondcleavagedirected by the carboxyl group. In marked contrast, the indole substrates react with diarylacetylenes accompanied by cleavage of the C2–H and C2′–H bonds and decarboxylation
palladium-catalyzed oxidative coupling reactions of N-substituted indoles or their carboxylic acid derivatives with alkynes. Unsymmetrically octasubstituted carbazoles can also be obtained by the stepwise couplings of 1-methylpyrrole-2-carboxylic acid with two different alkynes. In addition, the present coupling procedure is applicable to the synthesis of other various heteroarenes possessing di-, tri-, and tetracyclic