Benzamides with tethered acetal groups undergo reactions in CF3SO3H to give ring-fused isoindolinones by a cyclization cascade. The reaction initially forms an N-acyliminium ion which then gives the isoindolinone by the aza-Nazarov reaction. An unusual variant also cyclizes at the allylic position. (C) 2010 Elsevier Ltd. All rights reserved.