Pechmann reaction of 4‐hydroxycoumarins and thiocoumarins with cyclohexanone and ethyl cyclopentanone‐2‐carboxylates

The Pechmann reaction of 4‐hydroxycoumarins with cyclohexanone and ethyl cyclopentanone‐2‐carboxylates affords 1,2,3,4‐tetrahydro[2]benzopyrano[4,3‐c][1]benzopyran‐5,12‐diones and cyclopenta[3′,4′]pyrano‐[3,2‐c][1]benzopyran‐4,11‐diones. Dehydrogenation of the former yields [2]benzopyrano[4,3‐c][1]benzopyran‐5,12‐diones. Alkaline hydrolysis of a typical compound Va affords 2‐hydroxy‐2′‐carboxydeoxybenzoin which on boiling with acetic anhydride gives an isocoumarin derivative.