(±)-CSA catalyzed one-pot synthesis of 6,7-dihydrospiro[indole-3,1′-isoindoline]-2,3′,4(1H,5H)-trione derivatives: easy access of spirooxindoles and ibophyllidine-like alkaloids

The domino dehydration/condensation/cyclization sequence reaction of cyclic enaminones with 3-hydroxy-3-ethoxycarbonylisoindolin-1-one derivatives has been successfully realized for the first time in toluene at 90 °C by using a catalytic amount of commercially available inexpensive (±)-CSA (30 mol %). Gratifyingly, this novel domino protocol provides good to excellent yields of previously unknown class of 1-aryl/alkyl-substituted 6,7-dihydrospiro[indole-3,1′-isoindoline]-2,3,4(1H,5H)-trione derivatives. Moreover, biologically attractive spirooxindoles and ibophyllidine-like alkaloids have been prepared.