Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

Abstract

The selective visible-light-driven generation of a weak acid (sulfinic acid, in nitrogen-purged solutions) or a strong acid (sulfonic acid, in oxygen-purged solutions) by using shelf-stable arylazo sulfones was developed. These sulfones were then used for the green, smooth, and efficient photochemical catalytic protection of several (substituted) alcohols (and phenols) as tetrahydropyranyl ethers or acetals.

Visible-Light-Driven Solventylation Strategy for Olefin Functionalization

“… 18 The quantum yield value for the consumption of 2a (Φ –1 ) was 0.0031, lower than the one reported by Fagnoni (0.02) for the visible-light-driven generation of sulfinic acids in acetonitrile using the same compound. 12 The quantum yield for the acetonylation process Φ solv was found to be 0.0009, as expected, taking into account the complexity of the reaction pathway and the low quantum yield of the photoactive precursor.…”

“…However, the reaction initially failed in delivering the desired products with other solvents, affording the deprotected ketone precursor instead. This is probably due to the slightly acidic conditions developed in the reaction environment 12 when the substrate is not consumed at a sufficiently high rate. Switching the oxidant from potassium persulfate to BAIB allowed to isolate the desired products in moderate to good yields, the acetate ion slowly released being useful as a buffering agent to avoid the decomposition of the substrate.…”

“…Thanks to the presence of a dyedauxiliary group (N 2 SO 2 R), 10 followed by nitrogen loss from the so-obtained aryl diazenyl radical. 11 Since their peculiar photoreactivity, such compounds find multifaced applications in synthesis 10 as photoacid generators (PAGs) 12 and as initiators in free-radical polymerization. 13 In view of such premises, we report herein an arylazo sulfone-mediated synthetic platform that allows the visible light solventylation of alkenes by a large variety of organic solvents.…”

“…Thanks to the presence of a dyedauxiliary group (N 2 SO 2 R), 10 these derivatives absorb visible light in the 400–450 nm region (with e ranging 100–200 M –1 cm –1 ) and efficiently release an aryl/sulfonyl radical pair upon homolytic cleavage of the N–S bond followed by nitrogen loss from the so-obtained aryl diazenyl radical. 11 Since their peculiar photoreactivity, such compounds find multifaced applications in synthesis 10 as photoacid generators (PAGs) 12 and as initiators in free-radical polymerization. 13 …”

Friedel–Crafts arylation of aldehydes with indoles utilizing arylazo sulfones as the photoacid generator

“…15 a Among the different applications of arylazo sulfones in synthesis 15 and in chemistry of materials, 16 their use as non-ionic photoacid generators (PAGs) able to generate methanesulfonic acid in oxygen-saturated or air equilibrated solution has been recently investigated. 17 We thus decided to merge the experience of our groups to propose a fast, versatile and efficient procedure for the visible-light driven synthesis of diarylmethanes via Friedel–Crafts type synthesis of coupling of aldehydes and (hetero)arenes (Scheme 1e).…”