The acid-mediated ring opening/cyclisation reaction of N-benzyl-α-aryl-azetidinones

N-Benzyl-4-aryl-azetidinones undergo ring opening with triflic acid to form N-benzyl-cinnamamides, which either undergo cyclisation to give 5-aryl-benzazepin-3-ones or N-debenzylation to give cinnamamides.