Chiral compounds epoxides

The remarkable stereospecificity of TBHP-transition metal epoxidations of allylic alcohols has been exploited by Sharpless group for the synthesis of chiral oxiranes from prochiral allylic alcohols (Scheme 76) (81JA464) and for diastereoselective oxirane synthesis from chiral allylic alcohols (Scheme 77) (81JA6237). It has been suggested that this latter reaction may enable the preparation of chiral compounds of complete enantiomeric purity cf. Scheme 78) ... 

The hydrolytic kinetic resolution (HKR) of terminal epoxides using Co-salen catalysts provides a convenient route to the synthesis of enantioemiched chiral compounds by selectively converting one enantiomer of the racemic mixture (with a maximum 50% yield and 100% ee) (1-3). The use of water as the nucleophile makes this reaction straightforward to perform at a relatively low cost. The homogeneous Co(III) salen catalyst developed by Jacobsen s group has been shown to provide high... 

The catalytic asymmetric epoxidation of a,/i-unsaturated carbonyl compounds is one of the synthetically useful reactions in organic synthesis.The resulting chiral epoxides are easily converted to various useful chiral compounds. We developed a new yttrium-(5)-6,6 -[oxybis(ethylene)dioxy]biphenyl-2,2 -diol (1) (Figure 6.10)... 

Kinetic resolution.l33 Since enantiomers react with chiral compounds at different rates, it is sometimes possible to effect a partial separation by stopping the reaction before completion. This method is very similar to the asymmetric syntheses discussed on p. 102. An important application of this method is the resolution of racemic alkenes by treatment with optically active diisopinocampheylborane,134 since alkenes do not easily lend themselves to conversion to diastereomers if no other functional groups are present. Another example is the resolution of allylic alcohols such as 45 with one enantiomer of a chiral epoxidizing agent (see 5-36).135 In the case of 45 the discrimination was extreme. One enantiomer was converted to the epoxide and the other was not, the rate ratio (hence the selectivity factor)... 

Epoxides that have meso structures can be converted to optically active chiral compounds via enantioselective ring opening (Scheme 125). 

The methodology, including the use of other nucleophiles, can be used to produce chiral compounds from meso-epoxides in high yield.120-122... 

Precursor of Useful Chiral Ligands. OPEN is widely used for the preparation of chiral ligands. Organometallic compounds with these ligands act as useful reagents or catalysts in asymmetric induction reactions such as dihydroxylation of olefins, transfer hydrogenation of ketones and imines, Diels-Alder and aldol reactions, desymmetrization of meso-diols to produce chiral oxazolidinones, epoxidation of simple olefins, benzylic hydroxylation, and borohydride reduction of ketones, imines, and a,p-unsaturated carboxylates. ... 

The bulk of oxidations with tert-butyl hydroperoxide consists of epoxidations of alkenes in the presence of transition metals [147, 215, 216, 217, 218]. In this way, a,p-unsaturated aldehydes [219] and ketones [220] are selectively oxidized to epoxides without the involvement of the carbonyl function. Other applications of tert-butyl hydroperoxide such as the oxidation of lactams to imides [225], of tertiary amines to amine oxides [226, 227], of phosphites to phosphates [228], and of sulfides to sulfoxides [224] are rare. In the presence of a chiral compound, enantioselective epoxidations of alcohols are successfully accomplished with moderate to high enantiomeric excesses [221, 222, 223]. 

F. E. Kiihn, J. Zhao, W. A. Herrmann, Chiral monomeric organorhenium(Vll) and organomo-lybdenum(VI) compounds as catalysts for chiral olefin epoxidation reactions. Tetrahedron Asvmm. 16 (2005) 3469. 

A very different type of chemistry occurs when sulfur ylids add to carbonyl compounds. Epoxides are formed and recent progress with chiral sulfur ylids allows good asymmetric induction in this reaction. The easily prepared C2 symmetric sulfide 96 reacts with alkyl halides and then with aryl and alkyl aldehydes to give good yields of trans epoxides 97 with reasonable ees.19... 

Terminal alkenes other than allyl alcohol itself are not much use. The epoxide from one achiral type 75 is very susceptible to nucleophilic attack and the Payne rearrangement, while the other achiral type 76 gives poor ees. The chiral compounds 77 and 78 belong to the realm of kinetic resolution (chapter 28). 

In connection with investigations in the vitamin K series and considering the fact that some quinones and quinone epoxides are of importance in metabolic processes, the preparation of chiral quinone epoxides is of great interest. Such compounds were obtained with an e.e. of 45% by epoxidation of quinones using hydrogen peroxide in an alkaline medium in the presence of quininium benzyl chloride (QBC) [5]. 

Chiral epoxides and vicinal diols (employed as their corresponding cyclic sulfate or sulfite esters as reactive intermediates) are extensively employed high-value intermediates in the synthesis of chiral compounds because of their ability to react with a broad variety of nucleophiles (Figs. 11.2-1 and 11.2-2). In recent years, extensive efforts have been devoted to the development of chemo-catalytic methods for their production19, 10]. Thus, the Sharpless methods allowing for the asymmetric epoxida-... 

Tartarie acid [(/ ,/ )-20J is one of the most inexpensive chiral compounds available even the (.S. .S )-enantiomer, which does not occur so frequently in nature, is comparatively inexpensive, so there is no need for laboratory synthesis. Most diesters of both enantiomers are also inexpensive, at least for the C, - C3 alcohols. Tartaric acid itself has been used for the chiral modification of the surface of Raney nickel, which permits highly enantioselective reduction of carbonyl groups, e.g., of oxo esters, to the secondary alcohols (Section D.2.3.I.). The zinc salt of tartaric acid has been used for the asymmetric ring opening of epoxides by thiolates (Section C.). The diesters, e.g., 21-25, are conveniently obtained by acid-catalyzed esterification28-31, a method applicable to almost all alcohols as a typical example, dicyclohexyl (f ,tf)-tartrate is given32. 

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