Stereoselectivity asymmetric reactions

Chiral auxiliaries derived from (S)-proline appeared to be particularly attractive since they possess conformationally rigid pyrrolidine ring(s), a prerequisite to the above specified criteria. In this chapter highly stereoselective asymmetric reactions, employing the chiral diamines 1 and chiral diamino alcohols 2 and 3 (Fig. 1),... 

This chemical bond between the metal and the hydroxyl group of ahyl alcohol has an important effect on stereoselectivity. Asymmetric epoxidation is weU-known. The most stereoselective catalyst is Ti(OR) which is one of the early transition metal compounds and has no 0x0 group (28). Epoxidation of isopropylvinylcarbinol [4798-45-2] (1-isopropylaHyl alcohol) using a combined chiral catalyst of Ti(OR)4 and L-(+)-diethyl tartrate and (CH2)3COOH as the oxidant, stops at 50% conversion, and the erythro threo ratio of the product is 97 3. The reason for the reaction stopping at 50% conversion is that only one enantiomer can react and the unreacted enantiomer is recovered in optically pure form (28). 

In a catalytic asymmetric reaction, a small amount of an enantio-merically pure catalyst, either an enzyme or a synthetic, soluble transition metal complex, is used to produce large quantities of an optically active compound from a precursor that may be chiral or achiral. In recent years, synthetic chemists have developed numerous catalytic asymmetric reaction processes that transform prochiral substrates into chiral products with impressive margins of enantio-selectivity, feats that were once the exclusive domain of enzymes.56 These developments have had an enormous impact on academic and industrial organic synthesis. In the pharmaceutical industry, where there is a great emphasis on the production of enantiomeri-cally pure compounds, effective catalytic asymmetric reactions are particularly valuable because one molecule of an enantiomerically pure catalyst can, in principle, direct the stereoselective formation of millions of chiral product molecules. Such reactions are thus highly productive and economical, and, when applicable, they make the wasteful practice of racemate resolution obsolete. 

In 1960, Montanari and Balenovic and their coworkers described independently the first asymmetric oxidation of sulfides with optically active peracids. However, the sulphoxides were formed in this asymmetric reaction (equation 130) with low optical purities, generally not higher than 10%. The extensive studies of Montanari and his group on peracid oxidation indicated that the chirality of the predominantly formed sulphoxide enantiomer depends on the absolute configuration of the peracid used. According to Montanari the stereoselectivity of the sulphide oxidation is determined by the balance between one transition state (a) and a more hindered transition state (b) in which the groups and at sulphur face the moderately and least hindered regions of the peracid,... 

In recent years, the importance of aliphatic nitro compounds has greatly increased, due to the discovery of new selective transformations. These topics are discussed in the following chapters Stereoselective Henry reaction (chapter 3.3), Asymmetric Micheal additions (chapter 4.4), use of nitroalkenes as heterodienes in tandem [4+2]/[3+2] cycloadditions (chapter 8) and radical denitration (chapter 7.2). These reactions discovered in recent years constitute important tools in organic synthesis. They are discussed in more detail than the conventional reactions such as the Nef reaction, reduction to amines, synthesis of nitro sugars, alkylation and acylation (chapter 5). Concerning aromatic nitro chemistry, the preparation of substituted aromatic compounds via the SNAr reaction and nucleophilic aromatic substitution of hydrogen (VNS) are discussed (chapter 9). Preparation of heterocycles such as indoles, are covered (chapter 10). 

Dipolar cycloaddition reactions are of main interest in nitrile oxide chemistry. Recently, reviews and chapters in monographs appeared, which are devoted to individual aspects of these reactions. First of all, problems of asymmetric reactions of nitrile oxides (130, 131), including particular aspects, such as asymmetric metal-catalyzed 1,3-dipolar cycloaddition reactions (132, 133), development of new asymmetric reactions utilizing tartaric acid esters as chiral auxiliaries (134), and stereoselective intramolecular 1,3-dipolar cycloadditions (135) should be mentioned. Other problems considered are polymer-supported 1,3-dipolar cycloaddition reactions, important, in particular, for combinatorial chemistry... 

The asymmetric oxidation of organic compounds, especially the epoxidation, dihydroxylation, aminohydroxylation, aziridination, and related reactions have been extensively studied and found widespread applications in the asymmetric synthesis of many important compounds. Like many other asymmetric reactions discussed in other chapters of this book, oxidation systems have been developed and extended steadily over the years in order to attain high stereoselectivity. This chapter on oxidation is organized into several key topics. The first section covers the formation of epoxides from allylic alcohols or their derivatives and the corresponding ring-opening reactions of the thus formed 2,3-epoxy alcohols. The second part deals with dihydroxylation reactions, which can provide diols from olefins. The third section delineates the recently discovered aminohydroxylation of olefins. The fourth topic involves the oxidation of unfunc-tionalized olefins. The chapter ends with a discussion of the oxidation of eno-lates and asymmetric aziridination reactions. 

The chapter on alicyclic stereoselection has been splitted in two chapters (9 and 10). Chapter 10, which is exclusively devoted to Sharpless asymmetric epoxidation and dihydroxylation, has been rewritten de novo. The most recent advances in catalytic and stereoselective aldol reactions are incorporated in Chapter 9. 

Byk G, Kabha E (2006) A solid-supported stereoselective multicomponent reaction One-pot generation of three asymmetric carbons. Synlett 747-748... 

It seems that these asymmetric reactions include two important stereoselective steps ... 

Asymmetric transformations of ot-amino acids promoted by optically active metal complexes have been reported by several groups 269). The control of the stereoselective hydrolysis reactions of racemic esters by chiral micellar compounds prepared from amino acids has been intensively investigated 270). 

In 1996, McWilliams and coworkers described a very interesting tandem asymmetric transformation whereby an asymmetric 1,2-migration from a higher-order zincate 60 was coupled with a stereoselective homoaldol reaction (equation 26)29. 

Tor a treatise on this subject, sec Morrison Asymmetric Synthesis, 5 vols. [vol. 4 co-cditcd by Scott] Academic Press New York, 1983-1985. For books, see N6gr4di Stereoselective Synthesis VCH New York, 1986 Eliel Olsuka Asymmetric Reactions and Processes in Chemistry American Chemical Society Washington, 1982 Morrison Mosher Asymmetric Organic Reactions Prentice-Hall Englewood Cliffs, NJ, 1971, paperback reprint, American Chemical Society Washington, 1976 Izumi Tai, Ref. I. For reviews, see Ward Chem. Soc. Rev. 1990, 19, 1-19 Whitesell Chem. Rev. 1989, 89, 1581-1590 Fujita Nagao Adv. Heterocycl. Chem. 1989, 45, 1-36 Kochetkov Belikov Russ. Chem. Rev. 1987, 56, 1045-1067 Oppolzer Tetrahedron 1987, 43, 1969-2004 Seebach Imwinkelried Weber Mod. Synth. Methods 1986, 4, 125-259 ApSimon Collier Tetrahedron 1986, 42, 5157-5254 Mukaiyama Asami Top. Curr. Chem. 1985, 127, 133-167 Martens Top. Curr. Chem. 1984, 125, 165-246 Duhamel Duhamel Launay Plaqucvcnt Bull. Soc.Chim. Fr. 1984,11-421-11-430 Mosher Morrison Science 1983,221, 1013-1019 Schollkopf Top. Curr. Chem. 

Reviews on stoichiometric asymmetric syntheses M. M. Midland, Reductions with Chiral Boron Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 2, Academic Press, New York, 1983 E. R. Grandbois, S. I. Howard, and J. D. Morrison, Reductions with Chiral Modifications of Lithium Aluminum Hydride, in J. D. Morrison, ed.. Asymmetric Synthesis, Vol. 2, Chap. 3, Academic Press, New York, 1983 Y. Inouye, J. Oda, and N. Baba, Reductions with Chiral Dihydropyridine Reagents, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 4, Academic Press, New York, 1983 T. Oishi and T. Nakata, Acc. Chem. Res., 17, 338 (1984) G. Solladie, Addition of Chiral Nucleophiles to Aldehydes and Ketones, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 2, Chap. 6, Academic Press, New York, 1983 D. A. Evans, Stereoselective Alkylation Reactions of Chiral Metal Enolates, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 1, Academic Press, New York, 1984. C. H. Heathcock, The Aldol Addition Reaction, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 2, Academic Press, New York, 1984 K. A. Lutomski and A. I. Meyers, Asymmetric Synthesis via Chiral Oxazolines, in J. D. Morrison, ed., Asymmetric Synthesis, Vol. 3, Chap. 

D. A. Evans in Asymmetric Synthesis, Ed. J. D. Morrison, Academic Press, New York (1984), Vol 3, Chpt 1 (stereoselective alkylation reactions of chiral metal enolates)... 

---