Stereoselective organic synthesis

The reactions of the cycloamyloses may also be useful in achieving stereoselective organic synthesis or they may serve as models for hydrophobic interactions in aqueous solution. As the scope of cycloamylose catalysis is extended to include other reaction types and other cycloamylose derivatives, additional applications will undoubtedly be revealed for the cycloamyloses as catalysts. 

The enantioselective hydrogenation of prochirai heteroaromatics is of major relevance for the synthesis of biologically active compounds, some of which are difficult to access via stereoselective organic synthesis [4], This is the case for substituted N-heterocycles such as piperazines, pyridines, indoles, and quinoxa-lines. The hydrogenation of these substrates by supported metal particles generally leads to diastereoselective products [4], while molecular catalysts turn out to be more efficient in enantioselective processes. Rhodium and chiral chelating diphosphines constitute the ingredients of the vast majority of the known molecular catalysts. 

The following are selected applications of hydrogen peroxide oxidation of Si—C bonds in stereoselective organic synthesis (equations 76-78) ... 

This model of diastereoselectivity, schematized as to show the preferred approach toward erythro products, will surely be of use in stereoselective organic synthesis (Scheme 6.28) (21,22)... 

In the context of stereoselective organic synthesis, diastereofacial-selective cycloadditions of diazoalkanes and diazoacetates with functionalized alkenes has attracted some attention. 3,4-Disubstituted cyclobutenes were studied as dipolar-ophiles by the groups of Gandolfi and co-workers (113) and Martin and co-workers (114). The transition state structures of the cycloaddition of diazomethane with cis-3,4-dimethylcyclobutene was investigated theoretically by DPT methods (113a). 

There are about 25,000 enzymes present in nature and about 400 have been commercialised mainly for stereoselective organic synthesis and also for the biotechnological production of flavour compounds. The worldwide market for enzymes is more than US 1 billion. 

Warwel S, Sojka M, R6sch M (1993) Synthesis of Dicarboxylic Acids by Transition-Metal Catalyzed Oxidative Cleavage of Terminal-Unsaturated Fatty Acids. 164 79-98 Weinreb SM (1997) N-Sulfonyl Imines - Useful Synthons in Stereoselective Organic Synthesis. 190 131-184... 

Stereoselective Organic Synthesis of Nitiogen-containing Compounds 191... 

Further Development to Stereoselective Organic Synthesis of Nitrogen-containing Compounds... 

Antibodies combine some of the best features of synthetic and enzymatic catalysts. By fusing programmable design with the powerful selective forces of biology, this new technology has the potential to provide many valuable tools for stereoselective organic synthesis in the next century. 

Stereochemistry in radical reactions for organic synthesis has not been studied very extensively, because mild or low temperature-promoted radical reaction methods are extremely limited and the stereoselectivity in radical reactions is generally rather poor. Recently, however, stereoselective organic synthesis with radical reactions has become popular, since mild radical reaction methods such as the Barton decarboxylation, Et3B-initiated Bu3SnH reaction, etc. have been developed. Normally, low temperature-initiated radical reactions induce high stereoselectivity. 

As a further stereoselective organic synthesis [40-47] using reactive sp2 carbon-centered radicals, eq. 10.23 shows the preparation of chiral 4-te/7-butylcyclohexene (49) from the optically pure o-bromophenyl sulfoxide (48) through 1,5-H shift by sp2 carbon-centered radical, followed by (3-elimination. This reaction looks like a thermal concerted intramolecular elimination reaction (Ei). 

Recently, as mentioned above, stereoselective organic synthesis with high d.e. (diastereomer excess) and high e.e. (enantiomer excess) by means of the radical reactions, has been partly established under mild conditions. 

N-Sulfonyl Imines - Useful Synthons in Stereoselective Organic Synthesis... 

Notz W, Tanaka F, Watanabe S, Chaudari NS, Turner JM, Thayumanavan R, Barbas CF 3rd (2003) The direct organocatalytic asymmetric mannich reaction unmodified aldehydes as nucleophiles. J Org Chem 68 9624-9634 Noyori R (2002) Asymmetric catalysis science and opportunities (Nobel lecture). Angew Chem Int Ed Engl 41 2008-2022 Noyori R, Tokunaga M, Kitamura M (1995) Stereoselective organic synthesis via dynamic kinetic resolution. Bull Chem Soc Jpn 68 36-55 Ohkuma T, Kitamura M, Noyori R (2000) Asymmetric hydrogenation. In Ojima I (ed) Catalytic asymmetric synthesis, 2nd edn. Wiley-VCH, New York, p 1-110... 

Introduction. Homogeneous catalytic hydrogenation with cationic rhodium catalysts has been extensively explored by Schrock and Osborn. Use of these complexes in stereoselective organic synthesis has been a topic of more recent interest, and has been recently reviewed. The reagent of choice for many of these directed hydrogenations has continued to be [Rh(nbd)(dppb)]BF4 (1). 

Heathcock, C. H. The aldol condensation as a tool for stereoselective organic synthesis. Curr. Trends Org. Synth., Proc. Int. Conf., 4th 1983,27-43. 

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