Visible‐Light‐Mediated Dearomatisation of Indoles and Pyrroles to Pharmaceuticals and Pesticides

Abstract

Dearomatisation of indole derivatives to the corresponding isatin derivatives has been achieved with the aid of visible light and oxygen. It should be noted that isatin derivatives are highly important for the synthesis of pharmaceuticals and bioactive compounds. Notably, this chemistry works excellently with N‐protected and protection‐free indoles. Additionally, this methodology can also be applied to dearomatise pyrrole derivatives to generate cyclic imides in a single step. Later this methodology was applied for the synthesis of four pharmaceuticals and a pesticide called dianthalexin B. Detailed mechanistic studies revealed the actual role of oxygen and photocatalyst.

Visible‐Light Photoredox Catalyzed C−N Coupling of Quinoxaline‐2(1H)‐ones with Azoles without External Photosensitizer

“…However, imidazole and indole could not be used as effective nitrogen sources for the reaction under the present reaction conditions, and no desired products (3 aq and 3 ar) were obtained owing to the imidazole being more nucleophilic than pyrazole, [32] and indole being oxidized to the corresponding isatin with the aid of visible light and oxygen. [33] Subsequently, the scope of quinoxaline-2(1H)-ones was studied, and the results were summarized in Scheme 4. A variety of N-substituted quinoxalin-2(1H)-ones, such as N- methyl, N-ethyl, N-benzyl, N-acetyate, N-allylic, N-propynyl and N-2-oxo-2-phenylethyl ones were used to react with 2 a under the standard conditions, affording the according products (3 aa, 3 ba-3 ga) in 84 %, and 60-77 % yields.…”

Recent Developments in Photo‐Catalyzed/Promoted Synthesis of Indoles and Their Functionalization: Reactions and Mechanisms

“…In this review, these environmentally friendly synthetic strategies and their reaction mechanisms have been highlighted to access structurally diverse indole molecules. In particular, photoredox catalytic reactions for the synthesis of some natural products or pharmaceutical drugs bearing the indole nucleus are also developed [36,66,67,85,93,136,193] . For instance, Das et al.…”

“…For instance, Das et al. reported a visible‐light‐mediated dearomatisation of indoles to synthesize four pharamaceuticals and a pesticide dianthalexin B [136] . Recently, Qin et al.…”

“…Then, fragmentation of 254 and 255 respectively generates di-radical 256, followed by rearrangement to produce iminoketene intermediate Das and co-workers explored a visible lightinduced method to synthesize isatin derivatives via dearomatisation of indole derivatives (Scheme 88). [136] The mechanism experiments showed that O 2 and H 2 O should play an important role in this reaction. Indole initially combines with the generated singlet oxygen to give peroxo species 259, which further is oxidized to intermediate 260 via a second photocatalytic cycle.…”

Deal;Photoredox Catalysis for the Cycloaddition Reactions

“…Modern chemical syntheses are completely relying on the atom economical synthesis approach to enhance the sustainability. [1][2][3][4][5][6][7][8][9] Additionally, if the complex and valuable products can be achieved from easily available and cheap starting materials that should significantly increase the valorization potential of the methodology. [10][11][12][13] Based on this consideration, cycloaddition reactions are one of them which offer high valued cyclic products from cheap and easily available starting materials.…”