Graphene oxide nanosheets: a highly efficient and reusable carbocatalyst catalyzes the Michael-cyclization reactions of 4-hydroxycoumarins, 4-hydroxypyrone and 4-hydroxy-1-methylquinolinone with chalcone derivatives in aqueous media

Graphene oxide nanosheets were found to be a highly efficient, reusable and cost-effective carbocatalyst for the facile synthesis of highly diversified 4H-pyrans via a one-pot, two-component condensation reaction between freshly prepared chalcones and 4-hydroxycoumarin in aqueous media offering excellent yields. The new, green and metal free synthetic method also enables the condensation reaction for the formation of a library of pyranoquinolines and pyranopyrans.