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Inexpensive cobalt catalysts derived from N-heterocylic carbenes (NHC) allowed efficient catalytic C-H bond arylations on heteroaryl-substituted arenes with widely available aryl chlorides, which set the stage for the preparation of sterically hindered tri-ortho-substituted biaryls. Likewise, challenging direct alkylations with β-hydrogen-containing primary and even secondary alkyl chlorides proceeded on pyridyl- and pyrimidyl-substituted arenes and heteroarenes. The cobalt-catalyzed C-H bond functionalizations occurred efficiently at ambient reaction temperature with excellent levels of site-selectivities and ample scope. Mechanistic studies highlighted that electron-deficient aryl chlorides reacted preferentially, while the arenes kinetic C-H bond acidity was found to largely govern their reactivity.

A versatile nickel catalyst allowed for C-H alkylations of unactivated arenes with challenging secondary alkyl bromides and chlorides. The high catalytic efficacy also set the stage for direct secondary alkylations of indoles as well as C-H trifluoroethylations with ample substrate scope.

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A nickel complex derived from dppf, along with NaOt-Bu as the base, allowed for challenging aminations of aryl sulfamates. An improved functional group tolerance is observed in novel palladium-catalyzed aminations of imidazolylsulfonates with rac-BINAP as the ligand.

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Versatile nickel catalysts enabled the step-economical synthesis of decorated indoles through alkyne annulations with anilines bearing removable directing groups. The C-H/N-H activation strategy efficiently occurred in the absence of any metal oxidants and with excellent selectivities.

A nitrogen and phosphorus ligand-free catalytic system derived from inexpensive [(di-A C H T U N G T R E N N U N G glyme)NiBr 2 ] allowed for efficient direct C À H bond alkylations of heteroarenes with unactivated b-hydrogen-containing alkyl halides under basic reaction conditions. Keywords: alkylation; azoles; C À H activation; heterocycles; mechanism; nickel Substituted heteroarenes are indispensable substructures of, among others, biologically active compounds and functional materials. [1][2][3] In particular, strategies relying on direct C À H bond functionalizations arguably constitute the most ecologically benign and economically attractive methods for their preparation. [4] In recent years, various transition metal catalysts were devised for versatile direct arylations, alkenylations or alkynylations of heteroarenes by cleavages of unreactive C À H bonds.[5] In contrast, direct alkylations of (hetero)arenes with unactivated alkyl halides under basic reaction conditions continue to be difficult, predominantly because these challenging electrophiles lead to undesired b-eliminations.[6] Remarkable recent progress was represented by efficient ruthenium [7] and palladium catalyzed [8] direct alkylations of (hetero)arenes.[6] On the contrary, direct alkylations with less expensive nickel catalysts [9] are scarce, and were thus far solely achieved with nickel complexes derived from tridentate nitrogen ligands. [8g,10-12] Thus, Hu and co-workers elegantly devised the nickel complex [( Me NN 2 )NiCl] bearing a tridentate pincer N 2 Nligand for direct functionalizations of heteroarenes with alkyl halides.[10] Unfortunately, the synthesis of this catalyst involves several reaction steps, which can limit its broader applications.[13] Moreover, four direct alkylations of benzothiazole were recently achieved with a nickel complex derived from the tridentate nitrogen ligand terpyridine.[8g] Within our research program directed towards the development of userfriendly and sustainable C À H bond functionalizations, [14] we developed a cost-effective nitrogen-and phosphorus ligand-free [15] free nickel catalyst for direct alkylations of heteroarenes, on which we wish to report herein.At the outset of our studies, we tested a diverse array of commercially available nickel precursors for the direct C À H bond functionalization of benzoxazole (1a) with alkyl iodide 2a as the electrophile, 2,2'-bipyridine (bpy, 4) as the ligand, and CuI [10] as cocatalyst (Table 1). Among different nickel sources, [(di- Table 1. Nickel precursors for the direct C À H bond alkyla-A C H T U N G T R E N N U N G tion.[a] Entry[Ni] 3aaA C H T U N G T R E N N U N G [(diglyme)NiBr 2 ] 61%[a] Reaction conditions: 1a (1.0 mmol), 2a (1.5 mmol), [Ni] (5.0 mol%), CuI (7.5 mol%), 4 (6.0 mol%), t-BuOLi (2.0 mmol), 1,4-dioxane (3.0 mL), 140 8C, 16 h; isolated yields.