Diastereoselective Ritter reactions of chiral cyclic N-acyliminium ions: synthesis of pyrido- and pyrrolo[2,3-d]oxazoles and 4-Hydroxy-5-N-acylaminopyrrolidines and 5-hydroxy-6-N-acylaminopiperidines.
Pyrido- and pyrrolo[2,3-d]oxazoles can be conveniently prepared in high yield from the Ritter reaction of nitriles and in situ generated chiral cyclic N-acyliminium ions. cis-4-Hydroxy-5-acylaminopyrrolidines and cis-5-hydroxy-6-acylaminopiperidines can be readily obtained by acid hydrolysis of these bicyclic heterocyclic compounds, respectively.