A new entry into cis-3-amino-2-methylpyrrolidines via ring expansion of 2-(2-hydroxyethyl)-3-methylaziridines

3-Amino-2-methylpyrrolidines were prepared via a novel protocol, involving the reductive ring closure and O-deprotection of gamma-acetoxy-alpha-chloroketimines towards 2-(2-hydroxyethyl)-3-methylaziridines, followed by ring expansion of the latter into 3-bromopyrrolidines via intermediate bicyclic aziridinium salts and consecutive nucleophilic displacement of the bromo atom by azide towards 3-azidopyrrolidines. A final reduction of the azide moiety furnished 3-amino-2-methylpyrrolidines in high yields. Thus, a new formal synthesis of the antipsychotic emonapride was developed through preparation and further aroylation of cis-3-amino-1-benzyl-2-methylpyrrolidine.