Synthesis of C3-nitroalkylated-4-hydroxycoumarin and hydroxyiminodihydrofuroquinolinone derivatives via the Michael addition of cyclic 1,3-dicarbonyl compounds to β-nitrostyrenes

Herein, we describe a practical and efficient method for the C3-alkylation of 4-hydroxycoumarin by sonication under ‘on water’ conditions and mild temperatures using various substituted β-nitrostyrenes. In addition, we report on the development of a convenient process for the regioselective synthesis of angular hydroxyiminodihydrofuroquinolinone catalyzed by base. 4-Hydroxycoumarin and 4-hydroxy-1-methylquinolin-2(1H)-one reacted smoothly with various nitroolefins to furnish C3-nitroalkylated hydroxycoumarin derivatives (by sonication and ‘on water’ conditions) and hydroxyiminodihydrofuroquinolinone derivatives (ambient condition) as a mixture of Z (minor) and E (major) isomers, respectively. The mild reaction conditions employed, ease of isolation of the products and excellent yields constitute important features of the methodology.