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 CH 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.

Electrochemical Total Synthesis of Pyrrolophenanthridone Alkaloids: Controlling the Anodically Initiated Electron Transfer Process

“…Generally, temperature is an important factor for cyclization reactions. For example, it is known that the rotamer population of N -benzoyl indoline has a tendency to favor the trans -conformer at low temperature . For this reason, Pd-mediated intramolecular cross-coupling requires a high temperature (120 °C) to form the desired cis -conformer.…”