New Oligocyclic beta-Lactams and beta-Amino Acids 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 b-lactams 12 and 14, respectively. Under the reaction conditions, 12 undergoes lactam– amide bond cleavage to yield the bicyclic N-trifluoroacetylated b-amino acid derivative 13.