And asymmetric syntheses

A number of new and asymmetric syntheses of (S)-(-)-ipsenol (34) and (S)-(+)-ipsdienol (35), the pheromone of Ips bark beetles, were reported. Scheme 49 summarizes the synthesis of ipsenol by Riedeker and Steiner [75], which enabled them to prepare 56 g of (S)-34. They employed chiral auxiliary B derived from D-glucose. 

The hydroformylation reaction ( oxo reaction ) of alkenes with hydrogen and carbon monoxide is established as an important industrial tool for the production of aldehydes ( oxo aldehydes ) and products derived there from [1-6]. This method also leads to synthetically useful aldehydes and more recently is widely applied in the synthesis of more complex target molecules [7-15,17], including stereoselective and asymmetric syntheses [18-22]. 

Within a year of the publication of the stracture of platensimycin, Nicolaou s group had published both racemic and asymmetric syntheses of this molecule and recently expanded the base structure by constructing the adamantyl derivative of platensimycin (Figure 8.17) with the aim of substituting the more accessible adamantyl substituent in... 

Catalysts and procedures improve the selectivity of the metal-catalyst systems and asymmetric syntheses. Hydrogen-transfer and homogeneous catalysts offer alternatives to heterogeneous hydrogenation " . 

Lithiated phosphine oxides, the so-called Horner-Wittig reagents, are important intermediates in organic syntheses, for example in stereoselective syntheses of alkenes and asymmetric syntheses of chiral compounds [61, 62], Despite the importance of these reagents very little is known about their structures. The first lithiated phosphine oxide containing Li-C bonds has been reported recently. The self-assembled... 

As an illustration of achiral and chiral variants of the Mannich reaction leading to the same target molecule as a racemate or as an optically pure compound, in the next examples the retrosynthesis of the racemic form of fenpropimorph TM 4.16 and asymmetric syntheses of biologically active (5)-enantiomer are presented. 

The thallium(III)-mediated oxidative rearrangement of 1,2-dihydronaphthalenes has been explored intensively aiming the synthesis of indanes. The substrates on this transformation can be easily prepared from commercially available tetralones. The typical protocol is the use of TTN in MeOH or in trimethyl orthoformate (TMOF), which gives ring contraction products in excellent yield and diastereoselectivity. ° However, acetonitrile is the solvent of choice for some substrates bearing an alkyl group at the double. This rearrangement was used as the key step in the racemic and asymmetric syntheses of mutisianthol 48, which is a sesquiterpene with moderate antitumor activity (Scheme 18.12). 

In recent years, metal complexes are gaining importance as catalysts in synthetic and enzyme-like reactions. For example, nitrogen fixation. Cl chemistry, and asymmetric syntheses are among the most important topics in chemistry. It should be noticed that the reactivity of metal complexes depends not only on the nature of metal and substrate ligands but also on their interactions with other coexisting ligands. 

During the past decade, there has been an increased emphasis on new approaches to chiral compoimds and asymmetric syntheses. This focus has been particularly pronounced in medicinal chemistry, where a specific enantiomer or diastereomer often exhibits enhanced therapeutic potency compared with the racemate. Organofluorine compounds have played a significant role in these advances. An earlier report emphasized a range of methods for the synthesis of chiral bioactive fluoroorganic compounds (1). Since the intent of this paper is to provide an overview which captures the scope and flavor of these recent developments, it seems quite appropriate to briefly cite the fascinating range of research studies of the other contributors to this book. 

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