A new method for formylation of nitrogen heterocycles overcoming the limitations of classical approaches using a cheap feedstock formylating agent especially under mild and neutral conditions is the subject of this current investigation. This work describes direct formylation of nitrogen heterocycles (azaindoles, indoles, pyrroles) and anilines using glyoxylic acid as the formyl source and K2S2O8 as the exclusive reagent. The key features include a general method for both C‐ and N‐formylation under neutral and mild reaction conditions. The application of the method is further demonstrated in the tandem synthesis of nitrogen heterocycles, pharmaceuticals, and a natural product. Unlike aroylation with arylglyoxylic acids, a previously unknown pathway for the direct formylation with glyoxylic acid in the presence of K2S2O8 is now unveiled.
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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