Synthesis of 14 C‐labeled benzofurano[2,3‐b] benzopyran‐6‐one and its 4‐hydroxycoumarin derivative

2‐Isopropyl‐8,9‐dimethoxy‐benzofurano [2,3‐b]furo[2,3‐h] [1] [11‐ 14 C]benzopyran‐6‐one ( IVb ) and 3‐(2‐hydroxy‐4,5‐dimethoxyphenyl)‐4‐hydroxy‐5′‐isopropylfurano[2′,3′:7,8] [2‐ 14 C]coumarin( Vb ) were prepared from isorotenone ( Ib ) for use in metabolic and other studies. Deoxybenzoin derivative ( IIb ), obtained from isorotenone, was reacted with ethyl [ 14 C] formate in the presence of sodium to give the corresponding [2‐ 14 C]‐2′‐hydroxyisoflavone ( IIIb ), which was transformed into the 14 C‐labeled benzofurano [2,3‐b]furo[2,3‐h]benzopyran‐6‐one compound ( IVb ) by the subsequent oxidative cyclization with selenium dioxide. Hydrolysis of compound IVb in alkaline media gave 14 C‐labeled 4‐hydroxycoumarin ( Vb ).