Sterically stabilized α-lactams react by two distinct acid-catalyzed pathways. Protonation on oxygenresults in nucleophilic attack at the acyl carbon and gives C-2 products. Protonation on nitrogenleads to nucleophilic attack at the C-3 carbon and yields C-3 products. The mechanism thusdeveloped is very useful for understanding the changes in rates and product distributions in thereactions of sterically stabilized α-lactams with nucleophiles. It can also be extrapolated to otherα-lactams so that a more coherent picture of α-lactam reactivity can be developed.