Visible Light‐Induced Radical‐Radical Coupling: One‐Pot Synthesis of 6‐Benzyl‐6‐hydroxyindolo[2,1‐b]quinazolin‐12(6H)‐ones from Isatins and Potassium Benzyl Trifluoroborates

Abstract

A method for one-pot synthesis of 6-benzyl-6-hydroxyindolo[2,1-b]quinazolin-12(6H)-ones from isatins and potassium benzyl trifluoroborates was developed. Bioactive tryptanthrin skeleton can be constructed by visible light-induced radical-radical cross coupling, in which CÀ C and CÀ N bonds are formed in one pot. With this method, 31 products were synthesized directly from isatins in 22-86% yields. Notable features of this method include mild reaction conditions, metal-and external oxidant-free, and direct construction of highvalue complex structures from inexpensive and readily available starting materials.

Electrochemical and photochemical reaction of isatins: a decade update

“…3.1.1.5 One-pot synthesis of 6-benzyl-6-hydroxyindolo[2,1-b] quinazolin-12(6H)-ones. In 2022, He's group 33 investigated the reaction between isatin 1 and potassium benzyl trifluroborate 50 with 1,2,3,5-tetrakis(carbazol-9-yl)4,6-dicyanobenzene (4CzIPN) as photocatalyst under irradiation by 9 W blue LEDs and obtained the product in low yields (Scheme 30). Based on control experiments, they showed that the reaction required both light and a catalyst.…”

Skeletal Editing of Isatins for Heterocycle Molecular Diversity

“…In 2022, Guan and colleagues elucidated two routes (Method A and Method B) for the synthesis of tryptanthrin derivatives (Scheme 13). [39] Method A: Using two molecules of isatins 1 and potassium benzyl trifluoroborates 27 as the starting materials, the 6‐benzyl‐6‐hydroxyindolo[2,1‐b]quinazolin‐12(6H)‐ones 28 were obtained by visible light‐induced radical‐radical coupling. However, this strategy is limited by the structural diversity of the products.…”

Single Step Upgradation of Isatin to Bioactive Fused Heterocycles via Ring Expansion Reactions

“…The skeletal structure of tryptanthrin 73 includes the backbone of both indoles and quinoxalinones. A wide variety of drug molecules can be designed from tryptanthrins; hence, various pathways are used to synthesise them, and one such standard method is from isatin [53] . The building block of various naturally occurring alkaloids is constituted by ring‐fused quinazolinones such as rutaecarpine 74 , loutonin A 75 , mackinazolinone 76 , febrifugine 77 , vasicinone 78 , etc.…”

“…Here, they conducted experiments with different metal catalysts and finally concluded that FeCl 3 was the most appropriate one for the ring‐opening reaction of isatin with trifluroacetimidoyl chlorides 99 to produce 2‐(trifluoromethyl)quinazolin‐4(3 H )‐ones 103 (Scheme 21). Also, Huang and his group [53] focused on constructing 6‐benzyl‐6‐hydroxyindolo[2,1‐ b ]quinazolin‐12(6 H )‐ones 105 from a pseudo‐two‐component reaction of isatin and potassium benzyl trifluoro borates 104 in an inexpensive way. Here, two moles of isatin 1 reacted with one mole of potassium benzyl trifluoroborate 104 in the presence of a light source and a photocatalyst, 1,2,3,5‐tetrakis(carbazole‐9‐y l )4,6‐dicyanobenzene in a suitable solvent as shown in Scheme 22.…”