2, 2, -Disubstituted norbornenes (1, 2), 2, 2-Disubstituted norbornane (3), 2, 2, 3-trisubstituted norbornenes (4, 5), oxanorbornenes (6) and azanorbornenes (7) were synthesized by the Diels-Alder reaction using α, β-dehydroamino acids as a key step, and their antiulcer activities were examined. The oxazolidine derivative (1h) exhibited the most potent activities against several ulcer-models in rat.