Efficient metal-free visible light photocatalytic aromatization of azaheterocyles

Abstract

A metal free visible light photocatalytic oxidative aromatization of several aromatic azaheterocycles is reported using a newly developed 1,8-dimethoxy substituted acridinium ions (PC-2). With very low catalyst loading, it can photocatalyzed the oxidative dehydrogenation of differently substituted dihydropyridines, and pyrazolines to corresponding pyridines and pyrazoles in very short time and in most cases with near quantitative yield. This green photocatalytic aromatization method uses aerial oxygen as terminal oxidant to generate water as the only by-product. Scaling up experiment with 2 ​g of compound 1a, using 0.03% PC-2 catalyst loading, successfully demonstrated within 3 ​h to give 96% isolated product yield.

Keywords

• Metal free
• Visible light
• Oxidative aromatization
• Azaheterocycles
• Photoredox catalysis