Smooth Metal‐Free Photoinduced Preparation of Valuable 8‐Arylxanthines

Abstract

A set of 8‐arylxanthines was prepared under metal‐free conditions and in aqueous solvents from arylazo sulfones and caffeine or theophylline. Notably, the process took place by simply exposing the reaction vessel to visible or solar light, and unreacted xanthine could be easily recovered during the purification step.

Aryldiazonium Salts in Photoredox Catalysis – Recent Trends

“…In 2019, Fagnoni and co-workers established a protocol for the CÀ H arylation of xanthines with aryl azosulfones without any external photocatalyst. [52] The reaction proceeds smoothly under both sunlight (in a flow reactor) and blue light irradiation (in pyrex vessel). Mild to strong acids (HCOOH or HCl) were employed for xanthine's solubility since it precipitated during the reaction.…”

Dyedauxiliary Groups, an Emerging Approach in Organic Chemistry. The Case of Arylazo Sulfones

“…The same reactions were also optimized (in three different geographical locations, Germany, Italy, and Brazil) under flow conditions by adopting a solar microcapillary reactor (the so-called “Sunflow” apparatus), a device that allowed for an efficient conversion of the substrate after only 1 h of exposition to natural sunlight. A similar approach was exploited for the direct C–H arylation of caffeine 8a and theophylline 8b in aqueous acidic media . Indeed, it was demonstrated that the biological performance of a xanthine is significantly improved by the presence of an aryl group at the 8-position (as in compound 9 , Scheme a) .…”

“…A similar approach was exploited for the direct C−H arylation of caffeine 8a and theophylline 8b in aqueous acidic media. 33 Indeed, it was demonstrated that the biological performance of a xanthine is significantly improved by the presence of an aryl group at the 8-position (as in compound 9, Scheme 5a). 34 The process can be performed successfully also by using a 456 nm Kessil Lamp as the light source.…”

Metal‐Free Synthesis of Unsymmetrical Aryl Selenides and Tellurides via Visible Light‐Driven Activation of Arylazo Sulfones

“…[46] Such behavior was exploited in the development of several metal-free arylation protocols for the preparation, among the others, of aromatic stannanes, [47] phosphonates, [48] boranes, [49,50] sulfides [50] and arylated heterocycles. [51,52] We thus considered the opportunity of developing a visible light-driven procedure for the synthesis of aryl selenides and tellurides where neither catalyst nor additives were adopted (Scheme 1d).…”

“…[ 46 ] Such behavior was exploited in the development of several metal‐free arylation protocols for the preparation, among the others, of aromatic stannanes, [ 47 ] phosphonates, [ 48 ] boranes, [ 49,50 ] sulfides [ 50 ] and arylated heterocycles. [ 51,52 ]…”