Transition Metal-Mediated Couplings

Pyridones can also be converted to 2-chloropyridines by exchanging the carbonyl functionality using phosphoroxychloride (POCI3) [72]. A combination of N-halosuccinimides and triphenylphosphine has also been applied to introduce halogens in this position [73]. The carbonyl functionality in 2-pyridones makes these systems reactive towards nucleophiles as well, which add in 1,4-reactions with displacement of halides [74]. The use of transition metal mediated couplings like Heck, and Suzuki have also been successfully applied on halogenated 2-pyridones (d. Scheme 10) [36,75]. 

Replacement of a halogen by transition metal mediated coupling... 

The use of hypervalent iodine reagents in carbon-carbon bond forming reactions is summarized with particular emphasis on applications in organic synthesis. The most important recent methods involve the radical decarboxylative alkylation of organic substrates with [bis(acyloxy)iodo]arenes, spirocyclization of para- and ortho-substituted phenols, the intramolecular oxidative coupling of phenol ethers, and the reactions of iodonium salts and ylides. A significant recent research activity is centered in the area of the transition metal-mediated coupling reactions of the alkenyl-, aryl-, and alkynyliodonium salts. 

Numerous reactions of alkenyl(phenyl)iodonium salts leading to the formation of new C-C bond have been reported in the literature. The most important and synthetically useful reactions include the generation and subsequent cyclization of alkylidenecarbenes, alkenylation of carbon substrates via nucleophilic vinylic substitution, and transition metal-mediated coupling reactions. 

It can be anticipated that these areas of synthetic application will continue to attract significant research activity in the future. The increasing use of the transition metal-mediated coupling reactions of iodonium salts may add a new dimension to the field of polyvalent iodine chemistry. 

Almost all alkylations at the carbocyclic rings of quinolines are effected by metal-mediated processes either by quenching of a quinolyl organometallic species with a suitable electrophile or by transition metal-mediated coupling of a haloquinoline or quinolyltriflate with an alkylmetal derivative. 

Hydrostannylation represents another class of important reaction that often gives rise to interesting polymeric materials as well as precursors for transition metal mediated coupling transformations such as the Stille coupling protocol15. 

Intermolecular free-radical additions of stannyl radicals to multiple bonds have emerged as important methods for the preparation of tetraorganostannanes which can be reacted further to afford new C—C bonds through transition metal mediated coupling processes (e.g. Stille coupling). There are numerous examples of this chemistry715-737, and this treatise will focus on a few selected examples. 

There are a number of transition-metal mediated coupling reaction of aromatic substrates that probably proceed by radical coupling. It is also likely that many of these reactions do not proceed by free radicals, but rather by metal-mediated radicals or by ligand transfer on the metal. Reactions in these categories were presented... 

Other approaches to indoles based on transition metal-mediated couplings have been outlined in Sections 4.2.2 and 4.2.4. Nicolaou et al. recently described a novel solid-phase synthesis of substituted indolines and indoles [414]. 

Pyrrole itself tends to give tars under radical conditions, probably by way of initial N-hydrogen abstraction, but some A -substituted derivatives will undergo preparatively useful arylations, with attack taking place predominantly at an a-position. More efficient routes to arylpyrroles depend on transition metal-mediated coupling processes (see section 2.7.2.2). A -Methylpyrrole is attacked by electrophilic benzoyloxy radicals at its a-positions. ... 

Transition metal-mediated coupling of dihalo derivatives of EDOT... 

Crombie, A.L., Kane, J.L., Shea, K.M. and Danheiser, R.L. (2004) Ring expansion-annulation strategy for the synthesis of substituted azulenes and oligoazulenes. 2. Synthesis of azulenyl halides, sulfonates, and azulenylmetal compounds and their application in transition-metal-mediated coupling reactions. J. Org. Chem., 69, 8652-67. 

PEDOT PSS can be synthesized by (1) oxidative, (2) electrochemical, or (3) transition metal-mediated coupling polymerizations in the presence of a monomeric or polymeric counterion. The synthesis of PEDOT PSS by oxidative polymerization... 

Coupling Reactions to Dienes and Enynes. The silyl bromide (1) participates readily in copper or transition metal-mediated coupling reactions to produce 1,3-butadienes, which are very useful s)mthetic intermediates. For example, 2,3-bis[(trimethylsilyl)methyl]-1,3-butadiene (8), derived from the oxidative dimerization of cuprate (2) (M = Cu) is useful for rapid construction of multicyclic systems via tandem Diels-Alder reactions, as depicted in eq 15 The diene 2-dimethylaminomethyl-3-... 

Transition metal catalyzed coupling polymerization The most popular method for the s)mthesis of BDT based conjugated polymers takes advantage of the well-developed transition-metal mediated coupling reactions, featuring mild reaction conditions, remarkable functional group tolerance and high yields (Scheme 3.6). 

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