Recent advances in aryl–aryl bond formation by direct arylation

Abstract

The abundance of the biaryl structural motif in natural products, in biologically active molecules and in materials chemistry has positioned aryl-aryl (Ar-Ar) bond formation high on the agenda of synthetic chemists. For decades well-known reactions such as the Mizoroki-Heck and Suzuki-Miyaura have been the methods of choice to furnish biaryls. More recently, however, alternative methods, most notably direct arylation via C-H activation, have become the focus of many research groups. Compared to traditional methods, direct arylation affords Ar-Ar compounds in fewer steps by removing the need for prefunctionalisation. Furthermore, given that either one or two hydrogens are targeted, less waste and good atom economy are features of this methodology. This critical review covers, in the main part, reports from January 1, 2006, to October 22, 2008 (117 references).

Diketopyrrolopyrroles: Synthesis, Reactivity, and Optical Properties

“…Such methods may include direct arylation via the C-H bond activation [ 66a ] and oxidative coupling of aromatic compounds through C-H/C-H activation. [ 66 ] The possibility of the functionalization of DPPs by these methods was studied by Marder and co-workers. [ 68 ] Direct arylation involves the coupling of aryl halides (most often bromides) with notpreactivated arenes in the presence of transition metal catalysts (e.g., Pd) and bases.…”

“…[ 66 ] While the introduction of bromine atoms is relatively easy, the synthesis of boronic acids/ esters and organotin compounds is more troublesome (leading to anhydrous and anaerobic reaction conditions, low temperatures, and dangerous reagents such as BuLi). During the course of the Suzuki and Stille reactions, reactive groups are left as by-products, which may hinder the purifi cation of the desired products and is in confl ict with green chemistry rules (minimization of produced waste, the so-called 'atom economy').…”

“…[ 72 ] In contrast to direct arylation, oxidative arylation via C-H/C-H activation does not require any pre-activation of the starting materials. [ 66 ] The biaryl bond is formed through the oxidation of two aromatic C-H groups, which are activated by the palladium catalyst. This method was employed by Marder for the arylation of dithienyl DPP 52 .…”

“…Extensive development of the dehydrogenative coupling methodology in the last decade suggests the possibility that more cost-effective catalytic systems will appear in the near future, e.g., methods employing gaseous oxygen as the oxidant. [ 66 ] A convenient method for the synthesis of biaryl bonds is classical oxidative coupling of aromatic compounds. [ 73 ] Electron-rich arenes can be successfully coupled with simple and inexpensive oxidants, such as iron(III) chloride.…”

Iron‐Catalyzed Direct Arylation of Unactivated Arenes with Aryl Halides

“…[2,3] This strategy efficiently avoids the disposal of stoichiometric amounts of metal waste generated from the organometallic reagent, ArM, in the traditional coupling manner. [2,3] Various transition metals have been reported as efficient catalysts for this transformation, for example, Pd, [4][5][6][7][8][9][10][11] Rh, [12][13][14][15] Ru, [16][17][18] Ir, [19,20] Cu, [21][22][23][24][25][26][27] and other transition metals. [28][29][30] The application of inexpensive, non-toxic, commercially available, and environmentally benign iron complexes as catalysts in chemical syntheses has attracted much attention.…”