The electrophile−electrophile cross-coupling of carboxylic acid derivatives and alkylpyridinium salts via C−N bond cleavage is developed. The method is distinguished by its simplicity and steers us through a variety of functionalized ketones in good to excellent yields. Besides acid chlorides, carboxylic acids were also employed as acylating agents, which enabled us to incorporate acid-sensitive functional groups such as MOM, BOC, and acetal. Control experiments with TEMPO revealed a radical pathway.

Dedicated to Professor Oliver Reiser on the occasion of his 60th birthdayModern nickel-mediated cross-electrophile coupling reactions devoid of organometallic nucleophiles have garnered a great deal of interest due to their ability to enhance functional group compatibility. Despite the recent advances in the field, various mechanistic pathways, such as radical chain and sequential oxidative addition, in addition to finding the active nickel species and reductant, render the reaction complex. Although the reduction of Ni(II) complexes by heterogeneous Mn could produce either Ni(I) or Ni(0) species, the latter is more generally proposed as an active species. Likewise, Ni(I) mediated reduction of pyridinium salts is commonly invoked to generate the transient alkyl radicals. In stark contrast, we present a comprehensive mechanistic examination and experimental evidence for the intermediacy of Ni(I) species, a synergistic reduction of pyridinium salts by Ni(I) and Mn. Using a combination of kinetic analysis, control experiments, and spectroscopic methods, the rate-limiting reductive alkylation and resting state Ni(II) species have been identified.

Iron mediated catalytic reactions are of great interest in the field of organic synthesis because they are economic and naturally abundant. However, the use of iron catalyst in the field of free radical cyclization or reduction of alkyl halides remains limited. Here we describe the use of an unprecedented combination of iron and zinc in the reduction and 5‐exo‐trig radical cyclization of alkyl halides under mild condition in the absence of added ligands or additives. The method is distinguished by its wide scope, functional group tolerance and the use of 1,4‐cyclohexadiene as the source of hydrogen, which aids easy purification.

A simple and efficient iron-catalyzed protodehalogenation of alkyl and aryl halides using phenylhydrosilane is disclosed.