Successive Michael reactions on chromone derivatives with dimethyl 1,3-acetonedicarboxylate: one-pot synthesis of functionalized benzophenones, benzo[c]chromones and hydroxybenzoylfuroates

Chromones were reacted with dimethyl acetonedicarboxylate in the presence of DBU in THF at room temperature to furnish good yields of products, their structure depending on the substituent at 3-position. Unsubstituted chromones lead to methyl 7-hydroxy-6-oxo-6H-benzo[c]chromone-8-carboxylates 2, whereas by using 3-bromochromone, the methyl furoate 3c along with the unexpected furylcyclopropyl-chromene carboxylate 4c was isolated. Finally, from 3-formyl-chromones functionalized benzophenones 5 were isolated, in good yields. Plausible mechanisms are proposed.