Arene transition metal catalyzed coupling

Nanostructured Carbon Materials for Catalysis 24 Heterocycles from Double-Functionalized Arenes Transition Metal Catalyzed Coupling Reactions 25 Asymmetric Functionalization of C—H Bonds... 

Heterocycles from Double-Functionalized Arenes Transition Metal Catalyzed Coupling Reactions... 

With the success of transition-metal-catalyzed aryl-aryl cross-coupling reactions through C-H activation of one of the coupling partners, obviously, a more economic and attractive alternative is the coupling reaction via double C-H activation of two arenes, neither of which needs to be preactivated (Scheme 5). However, the development of such a process is very challenging because many difficulties remain to be solved. For instance, the control of selectivity when two coupling partners have more than one type of aromatic C-H bond is a challenge. 

For reviews on the Fujiwara-Moritani reaction, see (a) Fujiwara, Y. (2002) Palladium-promoted alkene-arene coupling via C—H activation, in Handbook of Organopalladium Chemistry in Organic Synthesis, Vol. 2 (eds E.-i. Negishi and A. de Meijere), John Wiley Sons, Inc., New York, pp. 2863-71 (b) Jia, C., Kitamura, T. and Fujiwara, Y. (2001) Catalytic functionalization of arenes and alkanes via C—H bond activation. Acc. Chem. Res., 34, 633-9 (c) Fujiwara, Y. and Jia, C. (2001) New developments in transition metal-catalyzed synthetic reactions viaC—H bond activation. PureAppl. Chem., 73,319-24 (d) Moritani, I. and Fujiwara, Y. (1973) Aromatic substitution of olefins by palladium salts. Synthesis, 524-33. 

The preparation of the PPV skeleton can be generally classified into two main strategies (i) olefinations methods to prepare the vinylene double bond and (ii) transition-metal-catalyzed single bond formation between the arene and vinylene components. The former includes Wittig-, Wittig-Horner- and Knoevenagel-type condensations, whereas the latter approach was demonstrated via Heck, Stille, Suzuki Miyaura and McMurry coupling reactions (Scheme 7.5). 

The possibilities for the formation of carbon-carbon bonds involving arenes have been dramatically increased in recent years by the use of transition metal catalysis. Copper-mediated reactions to couple aryl halides in Ulknann-type reactions [12, 13] have been known for many years, and copper still remains an important catalyst [14, 15]. However, the use of metals such as palladium [16,17] to effect substitution has led to such an explosion of research that in 2011 transition metal-catalyzed processes comprised more than half of the reactions classified as aromatic substitutions in Organic Reaction Mechanisms [18]. The reactions often involve a sequence outlined in Scheme 6.6 where Ln represents ligand(s) for the palladium. Oxidative addition of the aryl halide to the paiiadium catalyst is followed by transmetalation with an aryl or alkyl derivative and by reductive elimination to give the coupled product and legeuCTate the catalyst. Part 6 of this book elaborates these and related processes. 

Transition metal catalyzed hetero-[2+2+2] cycloaddition of alkynes to compounds with a multiple carbon-heteroatom bond such as isocyanates, carbon dioxide, nitriles, aldehydes, and ketones leads to heterocyclic arenes and unsaturated heterocycles. These reactions are classified into two groups coupling of diynes with multiple carbon-heteroatom... 

---