Substituent-directed reduction of cyclic aminals leading to two different heterocycles selectively: syntheses of functionalized nicotines and pyrido[2,3-b]azepines

Abstract

A new strategy of substituent-directed reductive ring-opening of aza-bridged pyridoazepine systems was designed and developed. The direction of the ring-opening is determined by the electron negativity of substituents attached to the nitrogen atoms. A plausible mechanism involving iminiums as the key intermediates to the two reaction pathways was proposed. The reductive cleavage reaction provides a convenient method to access novel 2-aminonicotine and pyrido[2,3-b]azepine derivatives.