New Oligocyclic (beta)-Lactams and (beta)-Amino Acid Derivatives by Intramolecular Cycloaddition of Bicyclopropylidenyl-Substituted Nitrones

Bicyclopropylidenylalkyl-substituted nitrones 6 and 7 undergo regio- and diastereoselective intramolecular cycloadditions to afford exclusively the ring-fused adducts 8 and 9, respectively. The thermal rearrangement of the cycloadducts 8 and 9 under acidic conditions (TFA) leads to the tricyclic (beta)-lactams 12 and 14, respectively. Under the reaction conditions, 12 undergoes lactam-amide bond cleavage to yield the bicyclic N-trifluoroacetylated (beta)-amino acid derivative 13.