Synthesis of fused-ring aza-dipyrromethenes from aromatic nitriles

Abstract

Aza-dipyrromethenes are ligands for a number of useful fluorescent dyes and electronic materials. They have high absorption in the red and NIR range. Fused-ring aza-dipyrromethenes cannot be synthesized through the same methods used to make aza-dipyrromethenes, which are common commercial dyes. The current synthesis is limited to treating a phthalonitrile-based electrophile with a Grignard reagent followed by reduction with formamide at high temperature. In this work, we introduce a new fused-ring aza-dipyrromethene synthesis from ortho-lithiated aromatic nitriles. This method allows for a much wider range of functional groups, less complicated starting materials, and yields that are consistent with the highest reported for aza-dipyrromethenes of any kind.