Transition metal catalysis substitution

Transition metal catalysis on solid supports can also be applied to indole formation, as shown by Dai and coworkers [41]. These authors reported a palladium- or copper-catalyzed procedure for the generation of a small indole library (Scheme 7.23), representing the first example of a solid-phase synthesis of 5-arylsulfamoyl-substituted indole derivatives. The most crucial step was the cydization of the key polymer-bound sulfonamide intermediates. Whereas the best results for the copper-mediated cydization were achieved using l-methyl-2-pyrrolidinone (NMP) as solvent, the palladium-catalyzed variant required the use of tetrahydrofuran in order to achieve comparable results. Both procedures afforded the desired indoles in good yields and excellent purities [41]. 

By far the most generally useful synthetic application of allyltributyltin is in the complementary set of transition metal- and radical-mediated substitution reactions. When the halide substrates are benzylic, allylic, aromatic or acyl, transition metal catalysis is usually the method of choice for allyl transfer from tin to carbon. When the halide (or halide equivalent) substrate is aliphatic or alicyclic, radical chain conditions are appropriate, as g-hydrogen elimination is generally not a problem in these cases. 

The application of transition metal catalysis provided new opportunities to introduce diverse functionality to the diazepine ring system. Iron-catalyzed cross-coupling of Grignard reagents with the imidoyl chloride 40 provided a convenient and efficient method for substituting the heterocyclic ring (Scheme 9) <20060L1771>. 

Apart form a great number of chiral NHC carbenes that have been used as ligands in enantioselective transition-metal catalysis (Gade and Bellemin-Laponnanz 2007), some less usual heterazolium salts have been tested in organocatalytic transformations. A planar-chiral thia-zolium salt (Pesch et al. 2004) and a rotaxane-derived precatalyst were reported (Tachibana et al. 2004), as well as catalytically active peptides containing an unnatural thiazolium-substituted alanine amino acid (Fig. 3 Mennen et al. 2005a,b). 

Bifiinctional conjunctive reagents (BCRs), such as a 1,3-substituted 2-methylenepropane (96), can serve as effective TMM synthons via transition metal catalysis. In this case, the transition metal complex can promote the elimination of the elements X—Y from (96) to form a coordinated TMM species. Cycli-zation of this intermediate with an alkene thus produces the methylenecyclopropane product and also regenerates the catalyst (Scheme 5). In the last decade a number of BCRs utilizing this concept, or some modifications thereof, has been developed for various TMM synthons. ... 

Many phosphane-substituted transition-metal clusters have been synthesized from late transition-metal carbonyl clusters and the appropriate phosphane using reductive ETC catalysis with reductive initiation [318-333]. Indeed such an initiation provides an exergonic cross electron-transfer propagation step. Most syntheses were carried out using a cathodic initiation or sodium benzophenone radical anion. The method was successful because it turned out that the first substitution of a carbonyl by a phosphane proceeds with high yield and coulombic efficiency in homoleptic metal carbonyl clusters and some others. 

The C-S bond of a sulfonium ylide can be cleaved thermally, photochemically, or by transition-metal catalysis, however, a number of acyl-substituted sulfonium ylides are not decomposed thermally at 70-80 C or catalytically with copper(II) sulfate (40-80°C). The so-formed oxocarbene (or metal complexes thereof) can, in principle, undergo 1,2-addition to... 

In addition to the very important palladium-catalysed reactions, boronic acids undergo a number of useful reactions that do not require transition-metal catalysis, particularly those involving electrophilic ipso-substitutions by carbon electrophiles. The Petasis reaction involves ip,y(9-replacement of boron under Mannich-like conditions and is successful with electron-rich heterocyclic boronic acids. A variety of quinolines and isoquinolines, activated by ethyl pyrocarbonate, have been used as the Mannich reagent . A Petasis reaction on indole 3-boronic acids under standard conditions was an efficient route to very high de a-indolylglycines. " ... 

Transition-metal catalysis on solid supports can also be used for indole formation [43]. A palladium or copper-catalyzed procedure has been described for generation of a small indole library (Scheme 16.21) this is the first example of solid-phase synthesis of 5-arylsulfamoyl substituted indole derivatives. Whereas the best... 

In our previous book on domino reactions [4h], we have classified domino reactions according to the mechanism of the different steps. This organizing principal will also be used in this book, and you will find chapters about transition metal catalysis including carbonylation, metathesis and CH-activation, nucleophiHc substitutions, radical reactions, pericyclic reactions, Michael reactions, aldol reactions, oxidations, and reductions. 

Pd-catalyzed site-selective cross-coupling reactions demonstrate the influential role of ligands in transition metal catalysis. The reactions described in this review discuss efficient approaches to introduce various substituents at specific halo-substituted posititMis (Ml (hetero)aromatic compounds. The commercial availability of a variety of dihalo-substituted starting materials makes site-selective crosscoupling reactions practical for the rapid production of diverse (hetero)arenes with multiple substituents. In all examples described here, the reactions proceeded successfully only on substrates containing hetero atoms, and this field of chemistry aims to include substrates without hetero atoms in the substrate scope. 

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