Synthesis of 4-(thien-2-yl)-substituted coumarins through Lewis acid catalyzed Michael addition of thiophenes to 3-benzoylcoumarins followed by oxidation

3-Benzoyl-4-(thien-2-yl)coumarins have been obtained in good yields according to the SNH addition–oxidation protocol, involving the diastereoselective addition of thiophenes at C-4 of 3-benzoylcoumarins under BBr3 catalysis, followed by oxidation of the intermediate 3,4-trans-3-benzoyl-4-(thien-2-yl)-3,4-dihydrocoumarins with DDQ. This two-step procedure can be regarded as nucleophilic substitution of hydrogen (SNH) on the heterocyclic ring of coumarins.

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