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

Abstract

A mild, inexpensive and sustainable protocol for the preparation of valuable bis-indolyl methanes via visible light-mediated, metal-free Friedel-Crafts arylation has been developed. The procedure, that exploits the peculiar behavior of...

Recent Advancements in Typical Friedel–Crafts Alkylation Reactions Focused on Targeting Arene Nucleophiles

“…In 2023, Kokotos and co-workers reported a versatile, inexpensive metal-free, visible-light-mediated sustainable approach for the FC arylation of aldehydes with indoles using irradiation at 456 nm and low-catalyst loading (0.5 mol%) of arylazo sulfone 10 as a non-ionic photoacid generator (PAG) to afford valuable bisindolylmethanes in high yields (Scheme 20 ). 115 Two examples using ketones gave the corresponding products in low yields.Various aldehydes and heterocyclic indoles were tolerated under the optimum reaction conditions.…”

Organocatalytic Friedel–Crafts arylation of aldehydes with indoles utilizing N-heterocyclic iod(az)olium salts as halogen-bonding catalysts

“…11 In 2023, the Kokotos’ group, in collaboration with the research groups of Fagnoni and Protti, proposed a fast, versatile and efficient procedure for the visible-light-driven synthesis of diarylmethanes via Friedel–Crafts-type coupling of aldehydes and (hetero)arenes, utilising arylazo sulfones as photoacid generators (PAGs) (Scheme 1F). 12 Among the different applications of arylazo sulfones in synthesis and chemistry of materials, their use as non-ionic photoacid generators (PAGs) is able to generate methanesulfonic acid in oxygen-saturated or air equilibrated solutions.…”

Arylazo sulfones: multifaceted photochemical reagents and beyond

“…As PAGs, arylazo sulfones have been employed for reactions such as photochemical catalytic protection of several (substituted) alcohols 43 (and phenols) (Scheme 36) 63 and carbonyl compounds 90 (Scheme 37) 65 and Friedel–Crafts arylations of aldehydes 90a with indoles 93 (Scheme 38). 66 Several (substituted) alcohols (and phenols) were protected as tetrahydropyranyl ethers or acetals 89 and carbonyl compounds 90 (81 examples) were protected as acetals/ketals 91 and 1,3-oxazolidines 92 in the presence of arylazo sulfones upon visible-light irradiation. The reactions featured a wide substrate scope, easy setup, and scalability up to 5 g. Indolyl methanes 94 were prepared in good to highly satisfactory yields via visible light-mediated, metal-free Friedel–Crafts arylation reactions employing a low-catalyst loading (0.5 mol%) and irradiation at 456 nm.…”