For over a century, chemical transformations of benzene derivatives have been guided by the high selectivity for electrophilic attack at the ortho/para positions in electron-rich substrates and at the meta position in electron-deficient molecules. We have developed a copper-catalyzed arylation reaction that, in contrast, selectively substitutes phenyl electrophiles at the aromatic carbon-hydrogen sites meta to an amido substituent. This previously elusive class of transformation is applicable to a broad range of aromatic compounds.

Transition-metal catalyzed reactions that are able to construct complex aliphatic amines from simple, readily available feedstocks have become a cornerstone of modern synthetic organic chemistry. In light of the ever-increasing importance of aliphatic amines across the range of chemical sciences, this review aims to provide a concise overview of modern transition-metal catalyzed approaches to alkylamine synthesis and their functionalization. Selected examples of amine bond forming reactions include: (a) hydroamination and hydroaminoalkylation, (b) transition-metal catalyzed C­(sp3)–H functionalization, and (c) transition-metal catalyzed visible-light-mediated light photoredox catalysis.

We have developed a new site-selective Cu(II)-catalyzed C-H bond functionalization process that can selectively arylate indoles at either the C3 or C2 position under mild conditions. The scope of the arylation process is broad and tolerates broad functionality on both the indole and aryl unit, which makes it amenable to further elaboration. The mechanism of the arylation reaction is proposed to proceed via a Cu(III)-aryl species that undergoes initial electrophilic addition at the C3 position of the indole motif. We speculate that site of indole arylation arises through a migration of the Cu(III)-aryl group from C3 to C2, and this can be controlled by the nature of the group on the nitrogen atom; free (NH)- and N-alkylindoles deliver the C3-arylated product, whereas N-acetylindoles afford the C2 isomer, both with excellent yield and selectivity.

The development of new chemical transformations based on catalytic functionalization of unactivated C-H bonds has the potential to simplify the synthesis of complex molecules dramatically. Transition metal catalysis has emerged as a powerful tool with which to convert these unreactive bonds into carbon-carbon and carbon-heteroatom bonds, but the selective transformation of aliphatic C-H bonds is still a challenge. The most successful approaches involve a 'directing group', which positions the metal catalyst near a particular C-H bond, so that the C-H functionalization step occurs via cyclometallation. Most directed aliphatic C-H activation processes proceed through a five-membered-ring cyclometallated intermediate. Considering the number of new reactions that have arisen from such intermediates, it seems likely that identification of distinct cyclometallation pathways would lead to the development of other useful chemical transformations. Here we report a palladium-catalysed C-H bond activation mode that proceeds through a four-membered-ring cyclopalladation pathway. The chemistry described here leads to the selective transformation of a methyl group that is adjacent to an unprotected secondary amine into a synthetically versatile nitrogen heterocycle. The scope of this previously unknown bond disconnection is highlighted through the development of C-H amination and carbonylation processes, leading to the synthesis of aziridines and β-lactams (respectively), and is suggestive of a generic C-H functionalization platform that could simplify the synthesis of aliphatic secondary amines, a class of small molecules that are particularly important features of many pharmaceutical agents.

Either the C2‐ or the C3‐substituted product can be obtained with the same palladium(II) catalyst in an oxidative intermolecular alkenylation of indoles. A variety of conditions can be used for derivatization at the 3‐position; however, the presence of acetic acid is required for the C2‐selective process (see scheme). Further elaboration of the products by a similar CH functionalization process leads to the bisalkenylated indoles selectively.