Catalytic asymmetric method

The discovery of viable substrate-direction represents a major turning point in the development of the Simmons-Smith cyclopropanation. This important phenomenon underlies all of the asymmetric variants developed for the cyclopropanation. However, more information regarding the consequences of this coordinative interaction would be required before the appearance of a catalytic, asymmetric method. The first steps in this direction are found in studies of chiral auxiliary-based methods. 

Of the numerous catalytic asymmetric methods developed for the functionalisation of alkenes, epoxidation has emerged as one of the most versatile and reliable methods... 

The paramount significance of chiral amines in pharmaceutical and agrochemical substances drives the development of efficient catalytic asymmetric methods for their formation. In contrast to the high enantioselectivities observed in asymmetric reduction of both alkenes and ketones, only limited success has been achieved in the enantiose-lective hydrogenation of imines [118]. Currently, there are few efficient chiral catalytic systems available for the asymmetric hydrogenation of imines. 

Since then, efficient catalytic asymmetric methods have been developed for the addition of silyl enol ethers or silyl ketene acetals to imines with chiral metal catalysts [29-34], Recently, direct catalytic asymmetric Mannich reactions which do not require preformation of enolate equivalents have appeared. 

In 2001, K. B. Sharpless won the Nobel Prize in Chemistry for his work on asymmetric aminohydroxylation and asymmetric epoxidation °. These stereoselective oxidation reactions are powerful catalytic asymmetric methods that have revolutionized synthetic organic chemistry. 

The last five years have witnessed explosive advances in the development of catalytic asymmetric methods. These have evolved for the most part from the seminal discovery by Mukaiyama that the addition of enoxysilanes and aldehydes is accelerated by Lewis acids. An impressive number and diversity of chiral Le-... 

The importance of a branched chiral amines in nature and as substructures in biologically active unnatural products led to the rapid development of an impressive number of methods to synthesize this class of compounds in enantiomerically enriched forms. It is quite spectacular to see how many very efficient methods have appeared since the early twenty first century. Furthermore, catalytic asymmetric methods now exist to transfer sp , sp, or sp nonstabilized carbanion nucleophiles to a wide range of activated imines. Even if the past 10 years have witnessed phenomenal advances in this area, Ellman s chiral auxiliary method is still very attractive. Indeed, it is the only one that allows the addition of the three kinds of nucleophiles using the same dass of reagents and it also possesses numerous other... 

Achiwa et al. [46,47,48,49] further developed the approach to access the monobutyrolactone skeleton by creating a very efficient catalytic asymmetric method. Aryldensuccinic acid mono-methyl esters (23), obtained by Stobbe condensation of dimethyl succinate and the corresponding substituted aldehydes, were enantioselectively hydrogenated using a neutral rhodium (I) complex of (4[Pg.550]

As was evident in the previous section, the main substrates for classical Pummerer reactions are sulfoxides. These are commonly obtained by the oxidation of sulfides. The oxidation can be performed with traditional oxidizing agents, such as Nal04, m-CPBA, and H2O2. Furthermore, the use of catalytic asymmetric methods for the selective oxidation of sulfides is well documented, and several synthetically applicable methods are described in the literature. ... 

The emergence of catalytic asymmetric methods to effect the Staudinger reaction appears to have largely displaced further efforts to identify new methodology based on the use of chiral auxiliaries. These methods rely on the nucleophilic activation of the ketene to form a zwitterionic enolate, which then undergoes nucleophilic addition to the imine, followed by cyclization. While the assembly of enantiodifferentiated transition states using Lewis acid catalysis has been well developed, the use of Lewis base catalysts to accomplish the same purpose is a relatively recent development and well suited to the Staudinger reaction. 

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