Aryldiazenyl Radicals from Arylazo Sulfones: Visible Light‐Driven Diazenylation of Enol Silyl Ethers

Abstract

A versatile protocol for the diazenylation of enol silyl ethers under visible light irradiation is presented herein. The reaction is based on the underused reaction of a nitrogen-based radical (the diazenyl radical) with an enol silyl ether. Arylazo sulfones were used as photoactivatable precursors of these diazenyl radicals. The resulting azaderivatives are potentially bioactive compounds as well as starting materials for the synthesis of N-containing heterocycles.

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

“…The photochemistry of arylazo sulfones was so far studied only for synthetic purposes − ,, in free-radical polymerization or for the functionalization of gold and graphene surfaces. This work clearly demonstrates that these compounds may be promising derivatives for the visible-light release of protons.…”

“…A dyed auxiliary group is a moiety which, once tethered to a molecule, makes the adduct colored and photoreactive. − As an example, the irradiation of arylazo sulfones leads to the homolytic cleavage of the N–S bond forming an aryldiazenyl radical and a methansulfonyl radical. The latter species can generate sulfinic acid ( VII ) in deoxygenated conditions (Scheme ) by hydrogen abstraction or methanesulfonic acid ( III , R = Me) in an oxygen-saturated solution. , Furthermore, arylazo sulfones exhibited a satisfactory thermal stability (some derivatives decompose over 145 °C) − and an excellent solubility in a wide range of organic media . In view of these premises, we focused on a set of shelf-stable, easy to synthesize arylazo sulfones having a substituent in the para ( 1a – g ), meta ( 1h – i ), or ortho ( 1j – k ) position (Figure ).…”

Simulating Electron Transfer Reactions in Solution: Radical-Polar Crossover

“…This barrier is in agreement with experimental barriers falling between 9.8 to 11.2 kcal/mol. 99 The formation of 4a is isoelectronic because it is uphill by only 0.2 kcal/mol. Since the nitrogen gas will bubble out of solution, this step is effectively irreversible and was removed from further simulations (4a to 4a').…”

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

“…As an example, trapping of the generated diazenyl radical by the π-bond system can occur before N 2 loss. This behavior was exploited for the diazenylation of enol silyl ethers to form a set of aza derivatives that exhibit bioactive properties and that found application in the synthesis of N -containing heterocycles …”