Facile Regioselective Synthesis of 3-amino-2-(2'-arylindanedionyl)indenones from 2-aryl-2,2'-biindan-1,1',3,3'-tetrones and Solvent-Dependent Keto-Enol Tautomerism in Enaminones

Refluxing 2-Aryl-2,2'-biindan-1,1',3,3'-tetrones in acetic acid with urea produces 3-amino-2-(2'- arylindanedionyl)indenones regioselectively within 2-3 h. in good yields. X-ray crystal structures of the products clearly indicate that in the solid state the compounds exist in the keto form. On the other hand NMR studies reveal that the enaminones exist in keto form in CDCl3 and in enol form in DMSO-d6 and acetone-d6.