Concerted synthesis of a spirobicyclic type-VI β-turn mimic of Pro-Pro-Pro-NH₂

A highly concerted strategy for the synthesis of symmetrical type-VI β-turn mimics was formulated. A proof of concept is presented in the synthesis of a spirobicyclic peptidomimetic of Pro-Pro-Pro-NH₂, compound 6. The formation of an unusual adduct that was encountered in the process also is reported. This approach is potentially general for type-VI β-turn mimics where the i + 1 and i + 2 residues are identical.