Tandem Cyclizations of 1,6‐Enynes with Arylsulfonyl Chlorides by Using Visible‐Light Photoredox Catalysis

A new era for homolytic aromatic substitution: replacing Bu3SnH with efficient light-induced chain reactions

“…Radical tandem 1,6-enyne cyclization was reported using the same catalyst with excited Ru(II) behaving as a reductant of 4-nitrophenylsulfonyl chloride (Scheme 14). 54 The substituent on the alkyne was important with the lowest yield of 28% obtained for the aliphatic alkyne (R 1 = hexyl), where 6-exo competed with 5-exo cyclization. Intermolecular HAS onto indoles, pyrroles and furans using diethyl bromomalonate is made possible by replacing the trialkylamine with an appropriate triarylamine of higher oxidation potential and that is unable to undergo competitive hydrogen atom transfer (Scheme 15).…”

“…52 Ru(I) acts as a reductant to give the cyclizing radical, and regenerating the catalyst with the source of the subsequent oxidation for the aromatic substitution less clear. Impressive cascade radical cyclizations using visible light photoredox catalysis have since been reported, 51,53,54 with the first being a 5-exo-trig followed by six-membered substitution onto indole (Scheme 13). Radical tandem 1,6-enyne cyclization was reported using the same catalyst with excited Ru(II) behaving as a reductant of 4-nitrophenylsulfonyl chloride (Scheme 14).…”

Synthesis of 6‐Alkylated Phenanthridine Derivatives Using Photoredox Neutral Somophilic Isocyanide Insertion

“…The photocatalysts B-D were also tested, but none of them gave better results (entries [6][7][8]. The base did not affect this transformation significantly and other bases, such as K 2 CO 3 , NaHCO 3 , and K 2 HPO 4 also gave good yields of the isolated products (entries [9][10][11]. Control experiments verified the necessity of the base, irradiation, and photocatalyst (entries [12][13][14].…”

“…While the palladium-catalyzed isocyanide insertions often require high reaction temperatures and have the tendency to undergo multiple consecutive insertions, [5] the use of isocyanides as somophiles for insertion reactions holds promise for practical synthetic applications under mild reaction conditions. [6] As a convenient approach to generate somophiles, photoredox catalysis, [7] which usually introduces alkenes, [8] alkynes, [9] and aromatic rings [10] as radical acceptors, has been widely used in the synthetic community to construct C À C bonds since 2008. [11] However, none of the reported work has employed photoredox catalysis to initiate isocyanide insertion.…”

Synthesis of 6‐Alkylated Phenanthridine Derivatives Using Photoredox Neutral Somophilic Isocyanide Insertion

“…] complex and a radical species (5). [7][8][9][10] The radical 5 adds to 1 to produce the imidoyl radical intermediate 6, which undergoes intramolecular homolytic aromatic substitution to give the radical intermediate 7. [14] The intermediate 7 is then oxidized by [fac-Ir(ppy) 3 4+ ] to form the cationic intermediate 8 and regenerates [fac-Ir(ppy) 3 ].…”