Synthesis of Morphinans through Anodic Aryl-Aryl Coupling

The morphinans are an important class of structurally fascinating and physiologically important natural products as exemplified by the famous opium alkaloids of the morphine family. Although this class of secondary metabolites from the juice of the opium poppy capsule was already used for medicinal purposes thousands of years ago, chemical modifications are still being applied to the core structure today in order to achieve the most specific effect on the various receptor subtypes possible with the fewest possible side effects. The unusual architecture of the morphinan core has also proven to be a highly challenging target for total synthesis. This review highlights electrosynthetic approaches towards natural and semisynthetic morphinan alkaloids. The historical progress in applying anodic aryl-aryl couplings to the construction of the morphinan framework is described in chronological order while particular benefits and challenges concerning the electrochemical transformations are grouped together, including the influence of substitution patterns, protecting groups, and reaction conditions.