Azabicyclo[4.3.0]- and [5.3.0]alkanone amino acid derivatives were easily prepared by submitting the same starting dipeptide to a direct ring-closing enyne metathesis or an ethylene-mediated cross-enyne metathesis/ring-closing metathesis, respectively. The reactivity of the newly synthesized 6,5- and 7,5-fused bicyclic scaffolds was then investigated to obtain variously functionalized derivatives with potential applications in the field of peptides/peptidomimetics.