Redox Condensations of <i>o</i>-Nitrobenzaldehydes with Amines under Mild Conditions: Total Synthesis of the Vasicinone Family

Abstract

A total synthesis of the vasicinone family of natural products from bulk chemicals was developed. Reductive condensation of o-nitrobenzaldehydes with amines utilizing iron pentacarbonyl as a reducing agent followed by subsequent oxidation leads to a great variety of polycyclic nitrogen-containing heterocycles under mild conditions. Enantiomerically pure vasicinone, rutaecarpine, isaindigotone, and luotonin were synthesized from readily available starting materials like hydroxyproline, nitrobenzaldehyde, pyrrolidine, and piperidine in two to four operational steps without chromatography. The antifungal activity of all products was tested.