Three-component synthesis of pyran-fused biscoumarins: an entry to pyridinone- and pyranone-fused coumarins.

A base-mediated, three-component synthesis of symmetric and unsymmetric pyran-fused biscoumarins via the coupling of 4-hydroxycoumarin with 4-chloro-3-formylcoumarin in ethanol is reported. This methodology is further extended to the construction of various indole/coumarin-substituted symmetric pyran-fused biscoumarins. The unsymmetric pyran-fused biscoumarin can react with amines and 4-hydroxycoumarins under basic and acidic conditions to afford pyridinone-fused coumarins and pyranone-fused coumarins, respectively. The mechanisms of their formation are proposed.