Ru-Catalysed synthesis of fused heterocycle-pyridinones and -pyrones.

The synthesis of fused heterocycle-pyridinones has been achieved by oxidative coupling of N-unprotected primary heterocycle-amides with internal alkynes. The reaction, which is catalysed by Ru(ii) and assisted by Cu(ii), takes place through C-H and N-H bond activation of the heterocyclic unit. The scope of the reaction includes a variety of alkynes, electron-rich thiophenes, furans and pyrroles, and even electron-poor pyridines. The reaction is fully regioselective with respect to the position of the C-H bond activation due to the directing effect of the amide group. In the same way, the synthesis of fused heterocycle-pyrones (isocoumarins) has been developed by Ru-catalysed oxidative coupling of heterocyclic carboxylic acids and internal alkynes. The reaction involves C-H and O-H bond activation. This reaction also has a broad scope, from electron-rich thiophenes, furans and pyrroles to electron-deficient pyridines and quinolines.