Aryl amines undergo smooth coupling with 2,2-dimethoxypropane (2,2-DMP) in the presence of 5 mol% of bismuth triflate under solvent-free conditions to produce 1,2-dihydroquinolines in high yields under mild conditions. However, the condensation of o-phenylenediamines with 2,2-DMP gave the corresponding 1,5-benzodiazepines in excellent yields under identical conditions. (C) 2007 Elsevier B.V. All rights reserved.