Modem organic synthesis

A central focus in modem organic synthesis has been the development of highly efficient catalytic processes for the syntheses of natural and unnatural compounds of medicinal interest or intermediates useful for functional materials. A particularly attractive approach is to apply transition metal catalysed cyclisation reactions for the transformation of simple starting materials into monocyclic, bicyclic and polycyclic scaffolds that can be further elaborated into specific targets. 

Another important reaction principle in modem organic synthesis is carbon-hydrogen bond activation [159]. Bergman, Ellman, and coworkers have introduced a protocol that allows otherwise extremely sluggish inter- and intramolecular rhodium-catalyzed C-H bond activation to occur efficiently under microwave heating conditions. In their investigations, these authors found that heating of alkene-tethered benzimidazoles in a mixture of 1,2-dichlorobenzene and acetone in the presence of di-//-... 

This problem has already been touched upon in previous sections. However, taking into account the importance of these reactions in modem organic synthesis, it is worthwhile to consider the main data in a special section. 

Alkoxycarbenium ions are important reactive intermediates in modem organic synthesis.28 It should be noted that other names such as oxonium ions, oxocarbenium ions, and carboxonium ions have also been used for carbocations stabilized by an adjacent oxygen atom and that we often draw structures having a carbon-oxygen double bond for this type of cations.2 Alkoxycarbenium ions are often generated from the corresponding acetals by treatment with Lewis acids in the presence of carbon nucleophiles. This type of reaction serves as efficient methods for carbon-carbon bond formation. 

The tetra-cA-cycIononatetracne 241 is unstable and easily rearranges at 23 °C (t /2 50 min) to the isomeric d.v-8,9-dihydroindcne 242 (equation 77)89. It is interesting, however, that the iron(III) tricarbonyl complex of tetraene 241 is stable for many days at room temperature and isomerizes to the Fe-complex of 242 only upon heating in octane at 101 °C89. The principle of stabilization of the reactive multiple bonds with metal carbonyl complexes is well-known in modem organic synthesis (e.g. see the acylation of enynes90). 

Gaspard-Iloughmane H, Le Roux C (2008) Bismuth(III) Lewis acids. In Yamamoto H, Ishihara K (eds) Acid catalysis in modem organic synthesis. Wiley, New York, p 551... 

The synthesis of sugars from noncarbohydrate substrates (total synthesis or de novo synthesis) has attracted the attention of organic chemists for more than 130 years [1], However, only the last 20 years have witnessed a rapid development of methods leading to structures of desired constitution and stereochemistry. Initially, sugars have been obtained as pure diastereoisomers in racemic form and, more recently, as pure enantiomers of desired configuration. This development is certainly correlated with the discovery of highly chemo- and stereoselective methods of modem organic synthesis. The subject of total... 

Kappe, C.O., Controlled Microwave Heating in Modem Organic Synthesis, Angewante Chemie International Edition, 43, 6250-6284 (2004). 

Kappe CO, Dallinger D (2009) Controlled microwave heating In modem organic synthesis highlights from the 2004-2008 literature. Mol Divers 13 71-193 and references therein Caddick S, Fitzmaurice R (2009) Microwave enhanced synthesis. Tetrahedron 65 3325-3355 and references therein... 

Both Tl and Tl form salts with many oxoanions. Thallium(I) salts have no direct uses, except perhaps as starting materials for other reactions. Thallium(III) salts, however, especially thallium(III) nitrate, have been widely used in modem organic synthesis. 

Metal enolates are widely used as building blocks in modem organic synthesis. A thorough understanding of their structure and reactivity is important, particularly since many of these... 

C-C bonds. It needs only to be emphasized that, in addition to the silyl enol ethers shown in the scheme, modem organic synthesis extensively employs enolates of boron, tin, titanium, zirconium, and other elements, as their utilization offers additional opportunities to achieve higher efficiency and exert control over the selectivity of the corresponding reactions. 

The special value of the Cope rearrangement in modem organic synthesis is due to the following characteristics, which provide a remarkable degree of specificity. 

This book is intended to be a guide to carrying out the types of reactions which are widely used in modem organic synthesis, and is concerned with basic technique. It is not intended to be a comprehensive survey of reagents and methods, but the appendix does contain some information on commonly used reagents. 

In modem organic synthesis, monosaccharides have a very well-developed chemistry that allows us to prepare almost any derivative and they are convenient sources of chirality. We hope that the material presented in this chapter will help the reader to plan the s)mthesis of optically pure targets using the known and convenient carbohydrate approach. 

Recently, the reactivity (base, nucleophile, catalyst) and the role in modem organic synthesis of N-heterocyclic carbenes (cychc carbenes bearing at least one amino substituent) has been set-up by Ender et al. [60,61]. The possible utilization of NHCs as ligands for transition-metal catalyst [62,63] and as organocatalyst has been emphasized [61]. The inversion of the normal reactivity (umpolung) induced via NHCs has been extensively discussed. Classical carbon-carbon-bond-forming reactions (benzoin condensation, Stetter reaction, etc.) have been re-examined using ionic liquids as pre-catalysts in the presence of bases. 

However, applications to modem organic synthesis are still very seldom and therefore the editors are very grateful to the two authors who contributed examples to this book. 

The direct functionalization of carbon-hydrogen bonds is becoming a powerful tool in modem organic synthesis. The installation of new functionality where none existed previously allows rapid introduction of complexity into simple molecules. Such methodology has the potential to revolutionize the field of chemical synthesis if certain key requirements are met. First of all, the transformations must be regi-oselective, since C-H bonds are ubiquitous in organic molecules. Second, they must be stereoselective to be useful in the context of complex molecule synthesis... 

Acid Catalysis in Modem Organic Synthesis, vol. 1 (eds H. Yamamoto and K. Ishihara ), Wiley-VCH Verlag GmbH, Weinheim, pp. 62-107 Terada M. (2008) Chem. Commun., 4097-4112. 

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