Insight into Transannular Cyclization Reactions To Synthesize Azabicyclo[X.Y.Z]alkanone Amino Acid Derivatives from 8‑, 9‑, and 10-Membered Macrocyclic Dipeptide Lactams

An efficient method for synthesizing different functionalized azabicyclo­[X.Y.0]­alkanone amino acid derivatives has been developed employing electrophilic transannular cyclizations of 8-, 9-, and 10-membered unsaturated macrocycles to form 5,5-, 6,5-, 7,5-, and 6,6-fused bicylic amino acids, respectively. Macrocycles were obtained by a sequence featuring peptide coupling of vinyl-, allyl-, homoallyl-, and homohomoallylglycine building blocks followed by ring-closing metathesis. X-ray crystallographic analyses of the 8-, 9-, and 10-membered macrocyclic lactam starting materials as well as certain bicyclic amino acid products provided insight into their conformational preferences as well as the mechanism for the diastereoselective formation of specific azabicycloalkanone amino acids by way of transannular iodolactamization reactions.