Studies on regioselectivity, of nitration of coumarins with cerium(IV) ammonium nitrate: Solid-state nitration of 6-hydroxy-coumarins on montmorillonite K-10 clay support under microwave irradiation

6-Hydroxycoumarins and their O-methyl ethers were selectively nitrated in the carbocyclic ring even in the presence of activating 4-Me group in the 2-pyrone ring with cerium(IV) ammonium nitrate (CAN) in acetic acid and acetonitrile in acceptable-to-excellent yields. Acetonitrile was found to be a better solvent for regioselective nitration than acetic acid. Use of CAN on montmorillonite K-10 clay under microwave irradiation for expeditious solvent-free regio-selective nitration has been revealed for the first time.