Ruthenium(II)-catalyzed synthesis of pyrrole- and indole-fused isocoumarins by C-H bond activation in DMF and water
Abstract
Pyrrole- and indole-fused isocoumarins constitute important structural units in natural products and pharmacophores, although the direct and selective bifunctionalization of pyrrole and indole remain a challenge. Herein, we report a one-pot synthesis of pyrrole- and indole-fused isocoumarins from simple 1-methylpyrrole-2-carboxylic acid and 1-methylindole-3-carboxylic acid by annulation with alkynes in the presence of a ruthenium(II) catalyst based on [RuCl<sub>2</sub>(p-cymene)]<sub>2</sub> with Cu(OAc)<sub>2</sub>-H<sub>2</sub>O as the oxidant in DMF. This ruthenium(II)-catalyzed transformation was shown to be profitably performed in water as the solvent. The reaction, which involves carboxylate coordination, activation of the heterocyclic sp<sup>2</sup> C-H bond, and insertion of the alkyne, is regioselective, which leads to good yields of the isocoumarins
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