A chemoselective reduction of nitro group in the presence of an aldehyde or ester group integrated with another synthetic transformation leading to the expedient synthesis of important heterocycles is the...
Aryl radical generation from the corresponding aryl halides using an electron donor and subsequent intramolecular cyclization with arenes could be an important advancement in contemporary biaryl synthesis. A green and practically useful synthetic protocol to access diverse six-and seven-membered biarylsultams especially with a free NH group including demonstration of a gram-scale synthesis is reported herein. The sulfoxylate anion radical (SO 2 −• ), generated in situ from the reagents rongalite or sodium dithionite (Na 2 S 2 O 4 ), was found to be the key single electron transfer agent forming aryl radicals from aryl halides, which upon intramolecular arylation gives biarylsultams with good to excellent yields. The approach features generation of aryl radicals that remained underexplored, use of a cheap and readily available industrial reagents, and transition metal-free, mild, and green reaction conditions.
Biaryl sultams represent a privileged molecular scaffold in drug discovery owing to their potential as a clinical candidate. Various developments toward the synthesis of diverse biaryl sultams including metal‐catalyzed and metal‐free CH functionalization involving CC/CN bond formation or annulative cyclization have been advanced in recent time. However, a transition metal‐catalyzed direct CH functionalization approach remains a powerful variant and has been utilized tremendously for the past several decades. The postsynthetic transformations of biaryl sultams to drug‐like molecules offer a tremendous possibility in drug discovery. In this article, we aim to provide an overview of various developments made in the synthetic approaches to biaryl sultams via CH functionalization, with a futuristic emphasis on their postsynthetic utility in accessing (hetero)biaryls containing an
ortho
‐sulfonamide or amine functionality, a promising and potentially useful molecular scaffold in therapeutic discovery. The current challenges and a future perspective are also discussed briefly.
A mild, operationally convenient, and practical method for the synthesis of synthetically useful N-arylsulfonylimines from N-(arylsulfonyl)benzylamines using K2S2O8 in the presence of pyridine as a base is reported herein. In addition, a “one-pot” tandem synthesis of pharmaceutically relevant N-heterocycles by the reaction of N-arylsulfonylimines, generated in situ with ortho-substituted anilines is also reported. The key features of the protocol include the use of a green oxidant, a short reaction time (30 min), chromatography-free isolation, scalability, and economical, delivering N-arylsulfonylimines in excellent yields of up to 96%. While the oxidation of N-aryl(benzyl)amines to N-arylimines using K2S2O8 is reported to be problematic, the oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines using K2S2O8 has been achieved for the first time. The dual role of the sulfate radical anion (SO4·−), including hydrogen atom abstraction (HAT) and single electron transfer (SET), is proposed to be involved in the plausible reaction mechanism.
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