Ionic-liquid-catalyzed green synthesis of coumarin derivatives under solvent-free conditions

• Published in: Chinese journal of catalysis 2013-09, Vol.34 (9), p.1690-1696
• Main Authors: Shaterian, H R, Aghakhanizadeh, M
• Format: Article
• Language: Chinese
• Subjects: Acetates
• ISSN: 0253-9837
• DOI: 10.1016/S1872-2067(12)60654-8

Broensted acidic ionic liquids, namely 2-pyrrolidonium hydrogen sulfate, N-methyl-2-pyrrolidonium hydrogen sulfate, N-methyl-2-pyrrolidonium dihydrogen phosphate, (4-sulfobutyl)tris(4-sul-fophenyl]phosphonium hydrogen sulfate, and triphenyl(propyl-3-sulfonyl)phosphonium toluenesulfonate, catalyzed efficient Pechmann condensation of phloroglucinol with beta -keto ethyl/methyl esters. 5,7-Dihydroxy-4-methylcoumarin and 5,7-dihydroxy-4-phenylcoumarin were prepared in good to excellent yields under mild, ambient, and solvent-free conditions. Pyrano[2,3-h] coumarins were then prepared by one-pot three-component reactions of 5,7-dihydroxy-4-subsituted coumarin, malononitrile, and aldehydes in the presence of catalytic amounts of Broensted basic ionic liquids, namely 2-hydroxyethylammonium formate, 3-hydroxypropanaminium acetate, 1-butyl-3-methylimidazolium hydroxide, pyrrolidinium formate, and pyrrolidinium acetate, under thermal solvent-free conditions. The catalysts are environmentally benign and can be easily prepared, stored, and recovered without significant loss of activity.