Benzofuranyl‐pyran‐2‐ones, ‐pyridazines, and ‐pyridones from naturally occurring furochromones (visnagin and khellin)

The novel and versatile enaminones 2a,b were synthesized by treatment of visnaginone methyl ether 1a or khellinone methyl ether 1b with N , N ‐dimethylformamide dimethylacetal. They were reacted with hippuric acid or N ‐acetylglycine to yield benzofuran‐5‐yl‐2H‐pyran‐2‐ones 3a–d . The reaction of 2a,b with cyanoacetamide and malononitrile dimer in sodium ethoxide gave benzofuran‐5‐yl‐pyridones 4a,b and [benzofuran‐5‐yl‐1H‐pyridine‐2‐ylidene] malononitrile 5a , respectively. Refluxing 2a,b with hydrazine hydrate or with hydroxyla‐ mine afforded benzofuran‐5‐yl‐1H‐pyrazoles 6a,b and benzofuran‐5‐yl‐isoxazoles 7a,b , respectively. Moreover, 2a,b coupled with aryl diazonium salt in the presence of sodium hydroxide to yield 3‐(benzofuran‐5‐yl)‐2‐aryl‐hydrazono‐3‐oxo‐propanals 8a,b which were excellent precursors for the synthesis of pyridazines 9–12 . © 2003 Wiley Periodicals, Inc. 15:85–91, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10219