Traceless-Activation Strategy for Rh-Catalyzed Csp 2 -H Arylation of Coumarins.

A traceless-activation strategy for the synthesis of 4-arylchroman-2-ones via a Rh(III)-catalyzed C-H activation of 2-arylpyridines and subsequent conjugated/decarboxylative addition to coumarin-3-carboxylic acids has been reported. The carboxyl group at C3 position of coumarin proved to be crucial to realize the reaction, which is spontaneously removed after the reaction by the release of CO2. The reaction displayed good substrate tolerance and gave various 4-arylchroman-2-ones in up to 90% yield.