Preparation of New 1,4‐Diazocanes as Scaffolds for Combinatorial Chemistry

Hexahydro‐2‐oxo‐1,4‐diazocin‐6‐carboxylic acid constitutes a conformationally rigid, crown‐shaped scaffold. An orthogonally protected (Boc at N‐4 and methyl ester at 6‐CO 2 H) representative was prepared by ring expansion of a 3‐pyrrolidone‐derived 1,4‐diketone with MeNH 2 . After deprotection, this building block was further diversified by reductive aminations and amidations and by sulfonamide and urea formation. Furthermore, the 6‐CO 2 H function was transformed into a 6‐NHCbz group in one step by carboxamide degradation in the presence of BnOH. An example of a cyclic tripeptoidic structure was synthesized by amidation with N ‐Boc‐β‐alanine and glycine methyl ester. Structural features of the eight‐membered heterocycle were established by single‐crystal X‐ray structure analysis of a 4‐bromoaniline derivative.