1.2- diols chiral

An extremely attractive feature of the route outlined at the beginning of this section for the transformation of boronates 3 or 4 to a-substituted allylboron compounds 5 is that reagents with very high enantiomeric purity (> 90% ee) may be prepared when precursors such as 3 and 4, and therefore also ate complex 1, contain a suitable diol chiral auxiliary17. The following syntheses of (S)-68, lib9, and 1310 illustrate this feature. 

Increasing interest is expressed in diastereoselective addition of organometallic reagents to the ON bond of chiral imines or their derivatives, as well as chiral catalyst-facilitated enantioselective addition of nucleophiles to pro-chiral imines.98 The imines frequently selected for investigation include N-masked imines such as oxime ethers, sulfenimines, and /V-trimcthylsilylimines (150-153). A variety of chiral modifiers, including chiral boron compounds, chiral diols, chiral hydroxy acids, A-sull onyl amino acids, and /V-sulfonyl amido alcohols 141-149, have been evaluated for their efficiency in enantioselective allylboration reactions.680... 

The Lewis acid catalyst 53 is now referred to as the Narasaka catalyst. This catalyst can be generated in situ from the reaction of dichlorodiisopropoxy-titanium and a diol chiral ligand derived from tartaric acid. This compound can also catalyze [2+2] cycloaddition reactions with high enantioselectivity. For example, as depicted in Scheme 5-20, in the reaction of alkenes bearing al-kylthio groups (ketene dithioacetals, alkenyl sulfides, and alkynyl sulfides) with electron-deficient olefins, the corresponding cyclobutane or methylenecyclobu-tene derivatives can be obtained in high enantiomeric excess.18... 

Ferrocenyl amido complexes, with Zr(IV), 4, 773 Ferrocenyl amino alcohols, synthesis, 6, 202 Ferrocenylated ODN, characteristics, 1, 909—910 Ferrocenyl diols, chiral, synthesis, 6, 204 Ferrocenyldiphenylphosphines, preparation, 6, 202 Ferrocenylimines mercuration, 2, 433 into platinacycles, 8, 511... 

Chiral 1,3-diols. Chiral p-alkoxy aldehydes react with compounds of the type RTiCI, at - 78° to form derivatives of 1,3-diols with high 1,3-asymmetric induction (equation I). High 1.3-asymmctric induction is also observed in aldol condensations of these aldehydes catalyzed by TiCL (equations II and III). 

This mutant has been developed by Ley, Hudlicky and others into a practical method for the asymmetric oxidation of substituted benzenes to give the unstable diols best preserved as acetals. Even one substituent is enough to make the diol chiral and dihydroxylation normally occurs at... 

Diols, chiral s.a. dichlorotitanium di-isopropoxide/diols, chiral under Titanium (IV) alkoxides, halogeno-... 

Desymmetrization of Prochiral and wieso-Diols. Chiral 1,3-propanediol derivatives are useful building blocks for the preparation of enantiomerically pure bioactive compounds such as phospholipids [176], platelet activating factor (PAF), PAF-antagonists [177], and renin inhibitors [178]. A simple access to these syn-thons starts from 2-substituted 1,3-propanediols (Scheme 3.8). Depending on the substituent R in position 2, (/ )- or (5)-monoesters were obtained in excellent optical purities using Pseudomonas sp. lipase (PSL) [179-182]. The last three entries demonstrate an enhancement in selectivity upon lowering the reaction temperature [183]. 

The low vapor pressure and high thermal stability of CILs render them suitable for enantioseparations in gas chromatography (GC). Recently, CILs have been used as chiral stationary phases (CSPs) in GC [40]. Armstrong and coworkers carried out enantiomeric separation of chiral alcohols and diols, chiral sulfoxides, some chiral epoxides and acetamides using a CIL based on ephedrinium salt. Using an ephedrinium CIL (4) as the CSP, enantiomeric separation of alcohols and diols was achieved (Fig. 1). The presence of both enantiomeric forms of ephedrine makes it possible to produce CSPs of opposite stereochemistry, which could reverse the enantiomeric elution order of the analytes. This offers an additional advantage that may not be easily achieved with common and widely used chiral selectors in GC such as the cyclodextrins. However, there was a decrease in enantiomeric recognition ability of the CSP after a week which the authors attributed to dehydration-induced... 

Sch6m6 2 Syntheses from chiral 1,2-diols. Chirality center. Possible racemization. 

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