Metal-assisted organic synthesis

This chapter has taken the reader through a number of microwave-assisted methodologies to prepare and further functionalize 2-pyridone containing heterocycles. A survey of inter-, intramolecular-, and pericyclic reactions together with electrophilic, nucleophilic and transition metal mediated methodologies has been exemplified. Still, a number of methods remain to be advanced into microwave-assisted organic synthesis and we hope that the smorgasbord of reactions presented in this chapter will inspire to more successful research in this area. 

Keywords Copper MAOS (Microwave assisted organic synthesis) Nickel Palladium Transition-metal-mediated bond formation... 

The reaction vessels used in microwave-assisted organic synthesis should preferably be made up of teflon, polystyrene or glass (Bose et al., 1994 Strauss and Train-or, 1995). These vessels should be tall and loosely covered with a capacity much greater than total volume of the reactants. Metallic containers are not advised for use as these are heated soon due to preferential absorption and reflection of rays. 

Such a broad range of classical elementary reactions of homogeneous catalysis with metal complexes, that can be facilitated by photons, make illumination of reaction solution a very useful instrument for substantial increase of the possibilities of homogeneous metal complex catalysis in organic synthesis. Particular examples of light-assisted syntheses will be given in section 3. 

Silver belongs to the late transition metals and, like gold, favors coordination to C=C triple bonds. A lot of silver-containing organometallic complexes, where silver-alkyne interactions assist the assembly of the complexes, are known. None of these complexes, however, was applied to efficient carbon-carbon bond formation in organic synthesis. 

There has been great interest in the area of chiral acid catalysts in organic synthesis over the past few decades. This topic has been the subject of several previous reviews. For example, the book Lewis Acids in Organic Synthesis (edited by Hisashi Yamamoto) was published by Wiley-VCH in 2000. In this chapter, successful and significant chiral Brpnsted acid catalysts, chiral Lewis acid catalysts [typical Lewis acidic elements main group elements, B(III) and Al(III), and early transition metal, Ti(IV)], and Lewis acid-assisted chiral Brpnsted acid catalysts developed after 2000 are discussed. Chiral acid/base catalysts wdl be discussed in Chapter 13 by Shibasaki and Kanai. 

An increasing number of microwave-assisted metal catalysis applications have been reported recently both for high-speed production of new chemical entities in early drug discovery and for other more general areas of organic synthesis. Although the number of examples on the application of solution-phase catalysis is steadily increasing, it is... 

The following contribution is intended to continue our earlier review [6] dealing with the then known cesium assisted ractions only some very important earlier cesium assisted reactions are described here for the sake of completeness After a short description of the properties of some cesium compounds used in this respect in organic synthesis, those reactions are discussed that have been published more recently and which proceed under the intermediate formation of organic cesium salts at oxygen, nitrogen or sulphur functions. Only those cyclization reactions are considered which allow a direct comparison of the yields obtained with cesium compounds or cesium metal. The description starts with reactions leading to the formation of C—C bonds and proceeds to the syntheses of ethers, lactones, amines and sulfides. The discussion ends with a summary of the attempts to explain the cesium effect . 

An important factor in the success of these reactions involves chelation-assistance by a heteroatom. Thus, the coordination of the heteroatom to the metal, brings the metal closer to the C-H bond and stabilizes the thermally unstable C-M-H species formed by the oxidative addition of a C-H bond to a low-valent transition metal complex. In addition, the use of the chelation-assistance leads to a high regioselectivity, which is an essential factor in organic synthesis. For reactions, a number of transition metal complexes - including ruthenium, rhodium, and iridium - are used as a catalyst, and ruthenium-catalyzed reactions will be described in this chapter [5]. 

Metal-assisted Grignard reactions that are useful in organic synthesis are scattered in the literature. This section collects several marked reactions. 

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