Superacid-catalysed arylation and rearrangement in 2 -hydroxy -2,2'-biindan-1,1'3,3'-tetrone and facile synthesis of 4-substituted phthalazinones

2-Hydroxy-2,2'-biindan-1,1',3,3'-tetrone 1 upon stirring with moderately activated and deactivated arenes in superacidic triflic acid (CF 3 SO 3 H, TfOH) medium produces arylated adducts 2-aryl-2,2'-biindan-1,1',3,3'-tetrones 3 within 1-2 h. Prolonged stirring (12-24 h) of the same reaction mixture gives rearranged products 3-(aryl-1,3-indanedionylmethylene)isobenzofuranones 4 involving three types of regioselectivity. The arylated adducts 3 and rearranged products 4 undergo nucleophilic ring opening and condensation with hydrazine hydrate to produce 4-substituted mono- and diphthalazinones depending upon the reaction temperature.