Ring Opening of Pyrolidine and Formation of N-Protected Amino Ketones; Synthesis of 5-Amino-2-pentanone Derivatives

피롤리딘의 개환과 N-프로텍티드 아미노 케톤의 형성; 5-아미노-2-펜타논 유도체의 합성

The base-induced elimination of N-protected 2-(bromomethyl)pyrrolidines 12a-c with KHMDS in THF at -78$^{\circ}C$ for 1h gave exocyclic enamines 13a-c. The acidic catalyzed pr otonation on ${\beta}$-carbon atom of 2-(methylene)pyrrolidines 13a-c with $H_3PO_4$ formed endocyclic N-iminium intermediates 14(or 15). Nucleophilic attack of alpha-carbon atom and hydrolysis of N-iminium ion gave carbocationic adduct (aminoalcohol) 16 from which 5-amino-2-pentanones 17a-c were formed after deprotonation.