Catalytic advances in direct functionalizations using arylated hydrazines as the building blocks

ABSTRACT Catalysis Changes the Scenario Phenyl hydrazine was the first hydrazine derivative prepared by Emil Fisher in 1875 for the characterization of sugars via hydrazones formation. Since then, various chemical applications have been demonstrated for hydrazines such as the synthesis of heterocyclic molecules like Fischer indole synthesis and hydrazone formation, among others. In the recent scenario, the catalytic decomposition of phenyl hydrazines and structurally similar phenylsulfonyl hydrazides has enabled unique reactivity properties and emerged as stable and readily available sources for diverse functionalizations by extruding small fragments like N2, SO2, and H2 gases in situ. Under mild oxidative conditions arylhydrazines leads to aryl radicals via the intermediate formation of instable diazenes. Due to these salient features, arylated hydrazines have gained considerable attention and serve as the building block for various important direct catalytic functionalizations such as Heck-type reactions, conjugate additions, C-H bond arylations, etc. Numerous catalytic methods have been developed utilizing arylated hydrazine; therefore, a focused anthology along with mechanistic insight will help in futuristic developments in direct functionalizations. Herein, we describe a focused compilation on the subject based on recent research in this direction. We have included recent articles (last 10 years) in this specific area describing applications and mechanistic aspects of the catalytic methodologies. Graphical Abstract