A structural study of seven N-acylindolines and their Pd(II)-mediated intramolecular oxidative coupling reactions for the synthesis of pyrrolophenanthridone alkaloids

Abstract

Direct synthesis of the pyrrolophenanthridone scaffold was explored using an intramolecular Pd(II)-mediated coupling reaction of different N-acylindolines via CH activation. Amaryllidaceae alkaloids of the lycorine type belong to this type. Depending on the substitution pattern of the starting materials, the pathway yielded different product patterns and yields. Introduction of electron-withdrawing substituents into the 6-position of the indoline moiety did not improve coupling. Seven N-acylindoline precursors were structurally characterized by X-ray crystallography and NMR spectroscopy. The crystal structure of the lycorine type alkaloid oxoassoanine is reported for the first time.