Binaphthol enantiomers

Lienne et al. [170] resolved the enantiomers of albendazole sulfoxides on a column derived from the 6S )-/V-(3,5-dinitrobcnzoyl)tyrosinc chiral selector. The developed method was applied for the enantiomeric resolution of albendazole sulfoxides in plasma samples. Witherow et al. [171] immersed a commercially available thin-layer plate (thin-layer chromatography) into a solution of N-(3,5-dinitrobenzoyl)-L-leucine solution. The developed plate was used for the chiral resolution of 2,2,2-trifluoro-(9-anthryl)ethanol and l,l -binaphthol enantiomers. 

Finally, a multireaction system will also be considered. The example is related to the separation of binaphthol enantiomers, and was reported by Morbidelli, Mazzotti and co-workers in some detail [1]. Separation of the enantiomers is even possible with an achiral stationary phase due to dimerization reactions taking place in the fluid phase. 

In this section, the application of equilibrium theory is illustrated for a fairly complex multireaction system. The problem to be considered is that of the separation of binaphthol enantiomers through using achiral chromatography. This problem was studied by Baciocchi et al. [1] among others, who in particular made the following experimental observations. When a pulse with a racemic composition of enantiomers was injected on to the column, no separation occurred. However in all cases... 

R. Baciocchi, G. Zenoni, M. Mazzotti, et al., Separation of binaphthol enantiomers through achiral chromatography. J. Chromatogr. 

In the presence of a catalytic amount of chiral lanthanide triflate 63, the reaction of 3-acyl-l,3-oxazolidin-2-ones with cyclopentadiene produces Diels-Alder adducts in high yields and high ee. The chiral lanthanide triflate 63 can be prepared from ytterbium triflate, (R)-( I )-binaphthol, and a tertiary amine. Both enantiomers of the cycloaddition product can be prepared via this chiral lanthanide (III) complex-catalyzed reaction using the same chiral source [(R)-(+)-binaphthol] and an appropriately selected achiral ligand. This achiral ligand serves as an additive to stabilize the catalyst in the sense of preventing the catalyst from aging. Asymmetric catalytic aza Diels-Alder reactions can also be carried out successfully under these conditions (Scheme 5-21).19... 

Recently, Schaumann et al. 153,154 an(j Bienz et tf/.155,156 have developed dependable routes for the resolution of racemic functionalized organosilanes with Si-centered chirality using chiral auxiliaries, such as binaphthol (BINOL), 2-aminobutanol, and phenylethane-l,2-diol (Scheme 2). For instance, the successive reaction of BINOL with butyllithium and the chiral triorganochlorosilanes RPhMeSiCl (R = /-Pr, -Bu, /-Bu) affords the BINOL monosilyl ethers 9-11, which can be resolved into the pure enantiomers (A)-9-ll and (7 )-9-11, respectively. Reduction with LiAlFF produces the enantiomerically pure triorgano-H-silanes (A)- and (R)-RPhMeSiH (12, R = /-Pr 13, -Bu 14, /-Bu), respectively (Scheme 2). Tamao et al. have used chiral amines to prepare optically active organosilanes.157... 

The bicapped tris-binaphthol (273), and its earlier-synthesized tris-biphenol analogue,are closely related to tris-catechol cages. The Fe + complex of (273) exists in A and A forms, derived from the two enantiomers—the six hydroxy groups impose helical chirality. 

A number of methods have been described (152) for the preparation of the bisbinaphthyl-22-ciown-6 derivative (55)-26 and its enantiomer. The best method is outlined in Scheme 7, starting from (5)-binaphthol. 

Uemura and coworkers utilized (R)-binaphthol 85 as chiral ligand in place of DET in association with Ti(IV)/TBHP, which not only mediated the oxidation of sulfides to (R)-configurated sulfoxides, but also promoted the kinetic resolution of sulfoxides (equation 50). In this latter process the two enantiomers of the sulfoxide are oxidized to sulfone by the chiral reagent at different rates, with decrease of the chemical yield, but increase of the ee values. Interestingly, the presence of ortho-nilro groups on the binaphthol ligand lead to the reversal of enantioselectivity with formation of the (5 )-configurated sulfoxide. Non-racemic amino triols and simple 1,2-diols have been successfully used as chiral mediators. 

Recently, Kobayashi found that both Diels-Alder adduct enantiomers were accessible with Yb(OTf)3 by using a single chiral source, (R)-binaphthol, and a choice of achiral ligands [45] (Eq. 8A.24). In the presence of 3-phenylacetylacetone (PAA) as the achiral ligand, one of the two active coordination sites in the chiral Yb catalyst is occupied, hence a dienophile coordinates to the remaining active sites, giving the other enantiomer selectively. 

Propylene sulfide (174) can also be polymerized enantiomer-selectively [252-262], In the polymerization with a ZnEt2-(-)-binaphthol initiator system at room temperature, the... 

Some amide derivatives have been reported to form inclusion complex with a wide variety of organic compounds.9 Optically active amide derivatives are expected to include one enantiomer of a racemic guest selectively. According to this idea, some amide derivatives of tartaric acid (11-13) were designed as chiral hosts.10 As will be described in the following section, these amide hosts were found to be useful for resolution of binaphthol (BNO) (14) and related compounds (15,16). 

The geometrical isomers and enantiomers of the overcrowded alkenes 15-18 can readily be separated using chiral HPLC. Recently, an asymmetric synthesis of overcrowded alkenes has been developed, involving chirality transfer from an axial single bond to an axial double bond (Scheme 8).32 This methodology is particularly attractive for preparation of larger quantities of enantiomerically pure chiral switches based on overcrowded alkenes. The orientation of the two xanthylidene moieties is dictated by a binaphthol template. After a coupling step and separation of the diastereomers, the bi-xanthylidene is obtained with 96 % e.e. after removal of the template. 

Pyridinecarbaldehyde reacts with trimethylsilyl cyanide in the presence of the catalysts derived from either enantiomer of 3,3 -bis(diethylaminomethyl)-substituted binaphthol or 1,1 -bi-2-naphthol (BINOL) and... 

Photocatalytic enantioselective oxidative arylic coupling reactions have been investigated by two different groups. Both studies involved the use of ruthenium-based photocatalysts [142, 143]. In 1993, Hamada and co-workers introduced a photostable chiral ruthenium tris(bipyridine)-type complex (A-[Ru(menbpy)3]2+) 210 possessing high redox ability [143]. The catalytic cycle also employed Co(acac)3 211 to assist in the generation of the active (A-[Ru(menbpy)3]3+) species 212. The authors suggested that the enantioselection observed upon binaphthol formation was the result of a faster formation of the (R)-enantiomer from the intermediate 213 (second oxidation and/or proton loss), albeit only to a rather low extent (ee 16 %) (Scheme 54). 

Racemic mixture and meso form, 19 separation of meso form racemate by chromatography, 223 irradiation converts the meso form to the racemate (R)-W enantiomer does not form a 19 complex with (5)-binaphthol,... 

They set up the catalytic reaction system depicted in Scheme 13. [Ru(menbpy)3]3 + is generated by oxidative quenching of [Ru(menbpy)3]2 + by the oxidant [Co(acac)3] (40, Hacac = pentane-2,4-dione). By oxidation of binaph-thol 38, [Ru(menbpy)3]3 + is converted to [Ru(menbpy)3]2 +. The oxidation products have not been established yet. With chiral A-[Ru(menbpy)3]3+ (S)-( — )-l,l -bi-2-naphtol (38) was converted faster than the (/ )-(+) enantiomer ent-38), so that after 3 h binaphthol ent-38 was obtained in 15% ee. 

Another interesting example is the optical resolution of the selenoxides by complexation with an optically active binaphthol [7]. The resolution proceeded very efficiently owing to the facile racemization of the selenoxides and in some cases an optically pure selenoxide was obtained in more than 100% chemical yield based on the initial enantiomer [7]. 

Bao and Wulff compared catalysts prepared from vaulted biaryls and from bromo-borane dimethylsulfide with those generated from linear biaryls with regard to their capacity to provide enantioselective induction in the Diels-Alder reaction of cyclo-pentadiene and methacrolein (Eqs 6 and 7) [7]. Because the (5) enantiomers of vaulted biaryls result in induction opposite to that resulting from use of the (5) enantiomer of binaphthol, and because effective catalysts cannot be generated from binaphthol and phenylboron dichloride, suggest that the catalysts obtained from vaulted biaryls do not have the same structure as the Cs-symmetrical catalyst produced from binaphthol. 

Also, it is expected that the micellar size is controlled easier than with a conventional low-molecular-mass surfactant (EMMS). The first report on enantiomer separation by MEKC using a chiral HMMS appeared in 1994, where poly(sodium A-undecylenyl-L-valinate) [poly(L-SUV)] was used as a chiral micelle and binaphthol and laudanosine were enantioseparated. The optical resolution of 3,5-dinitrobenzoylated amino acid isopropyl esters by MEKC with poly(sodium (10-undecenoyl)-L-valinate) as well as with SDVal, SDAla, and SDThr was also reported. 

Rac/meso-isomers of bridged bis(indenyl) zirconium dichlorides can interconvert photochemically.796 This interconversion has been utilized in the stereoselective synthesis of ansa-zirconoccnc binaphtholate stereoisomers.797 Specifically, the rac-meso-mixtures 1034 induced by irradiation in toluene react with 1 equiv. of the dilithium salt of racemic binaphthol to give the racemic binaphtholate complex 1035 (Scheme 253). Analogous reactions with 1 equiv. of the Z (+) enantiomer of dilithium binaphtholate afford the enantiomerically pure binaphtholate complex. The structure of the racemic binaphtholate complex, Me2Si(2-Me-4-But-C5H2)2Zr(binaphtholate), has been crystallographically determined. 

Q1. 2,2 -Binaphthol (54) is a chiral biaryl that is used in asymmetric synthesis. Determine the configuration of the enantiomer shown in 54. 

---