Denitrogenation of tosylhydrazones: synthesis of aryl alkyl sulfones catalyzed by a phenalenyl-based molecule

Sulfur-containing organic molecules such as sulfones are prevalent in pharmaceuticals and agrochemicals. Herein, we report the first transition-metal-free process for in situ denitrogenation of tosylhydrazones to produce a diverse array of aryl alkyl sulfones. We have used phenalenyl-based odd alternant hydrocarbon as a photoredox catalyst for denitrogenation of tosylhydrazones, where the phenalenyl acts as a potent oxidant to form a sulfinate radical intermediate from a sulfinate anion. We performed radical trapping, in situ electron paramagnetic resonance (EPR), and fluorescence quenching studies to elucidate the plausible mechanism. This method shows wide functional-group tolerance, with applications in late-stage modification of various natural products with good to high yields. The protocol provides an easy method for the synthesis of sulfones. An efficient method is developed for the photoinduced generation of a radical species based on the smallest odd alternant polyaromatic hydrocarbon phenalenyl, and its application in redox catalysis for denitrogenative sulfonylation of tosylhydrazones.

Automated summary

This article reports a transition-metal-free process for in situ denitrogenation of tosylhydrazones, resulting in the production of various sulfones. The authors used a phenalenyl-based odd alternant hydrocarbon as a photoredox catalyst, which acted as a potent oxidant to facilitate the denitrogenation reaction. The method showed wide functional-group tolerance and high yields, making it suitable for late-stage modification of natural products.