The direct monoarylation of ammonia for the synthesis of aniline derivatives constitutes a significant challenge in modern synthetic chemistry. Over the past decade, major efforts have been made in order to develop highly active and selective catalyst systems for this transformation. More specifically, the application of various transition-metal catalysis has enabled substantial progress in substrate scope and reaction conditions as well as catalyst costs and availability. This review describes these advancements focusing on palladium-, copper-, and nickel-based catalyst systems that have been reported until mid-2017.

A novel methodology for the direct nitration of arylboronic acids has been developed. By using inexpensive tert-butyl nitrite various aromatic nitro compounds are produced in moderate to good yields (45-87%) without the need of any catalyst.

Scheme 1. Carbonylative three component CÀC coupling reactions. TM = transition metal.

Iron-catalyzed reductions: Selective iron-catalyzed reduction of aldehydes with hydrogen generated in situ by the water-gas shift reaction is presented (see scheme). The generality and selectivity of this mild procedure are demonstrated by the efficient reduction of various aromatic, aliphatic and α,β-unsaturated aldehydes.

The challenging nickel‐catalyzed mono‐α‐arylation of acetone with aryl chlorides, pivalates, and carbamates has been achieved for the first time. A nickel/Josiphos‐based catalytic system is shown to feature unique catalytic behavior, allowing the highly selective formation of the desired mono‐α‐arylated acetone. The developed methodology was applied to a variety of (hetero)aryl chlorides including biologically relevant derivatives. The methodology has been extended to the unprecedented coupling of acetone with phenol derivatives. Mechanistic studies allowed the isolation and characterization of key Ni0 and NiII catalytic intermediates. The Josiphos ligand is shown to play a key role in the stabilization of NiII intermediates to allow a Ni0/NiII catalytic pathway. Mechanistic understanding was then leveraged to improve the protocol using an air‐stable NiII pre‐catalyst.