1,1 -Binaphthyl, resolution

Recrystallization of a 1 1 molecular complex formed from several sulfoxides and (R)-( + )-2,2 -dihydroxy-l, l -binaphthyl (7) allowed resolution of the former22. Conversely, using the optically pure sulfoxide, it was possible to resolve racemic bis-naphthol 7. 

A new approach to the resolution of sulphoxides 242 was recently reported by T oda and coworkers282. It takes advantage of the fact that some sulphoxides form crystalline complexes with optically active 2,2 -dihydroxy-l, 1-binaphthyl 243. When a two-molar excess of racemic sulphoxide 242 was mixed with one enantiomeric form of binaphthyl 243 in benzene-hexane and kept at room temperature for 12 h, a 1 1 complex enriched strongly in one sulphoxide enantiomer was obtained. Its recrystallization from benzene followed by chromatography on silica gel using benzene-ethyl acetate as eluent gave optically pure sulphoxide. However, methyl phenyl sulphoxide was poorly resolved by this procedure and methyl o-tolyl, methyl p-tolyl, s-butyl methyl and i-propyl methyl sulphoxides did not form complexes with 243. 

The strategy described here explains the different possibilities of enzymatic ammonolysis and aminolysis reaction for resolution of esters or preparation of enantiomerically pure amides, which are important synthons in organic chemistry. This methodology has been also applied for the synthesis of pyrrolidinol derivatives that can be prepared via enzymatic ammonolysis of a polyfunctional ester, such as ethyl ( )-4-chloro-3-hydroxybutanoate [30]. In addition, it is possible in the resolution of chiral axe instead of a stereogenic carbon atom. An interesting enzymatic aminolysis of this class of reaction has been recently reported by Aoyagi et al. [31[. The side chain of binaphthyl moiety plays an important role in the enantiodis-crimination of the process (Scheme 7.14). 

Scheme 7.14 Resolution of a binaphthyl ester by an ammonolysis reaction.

An optically active polymethacrylate (2) having a binaphthol moiety in the side chain was synthesized by radical polymerization. This polymer coated on silica gel resolved several racemates.50 However, no data on the influence of the stereoregularity of the main chain on resolution have been reported. The chiral recognition by this polymer may simply arise from the binaphthyl group. 

Chiral 1,1 -binaphthol derivatives are well established as readily available chiral catalysts and auxiliaries for the production of various useful optically active compounds. Tanabe et al. investigated [11] a crystalline-liquid resolution of (1R) -// . v - c h rysanthemic acid utilizing l,l -binaphthyl monoethyl ether (25) (Scheme 3). 

Scheme 3 Optical resolution with l,l -binaphthyl monoethyl ether...

The reactions can be carried out under mild conditions in the presence of triethylamine or an inorganic base such as potassium carbonate,388 and under the latter conditions, the kinetic resolution of PhCH(OH)CH2CH2OH has been achieved using a chiral stannoxane based on 1,1 -binaphthyl. 

The use of vinyl epoxides as substrates in enantioselective copper-catalyzed reactions, on the other hand, has met with more success. An interesting chiral ligand effect on Cu(OTf)2-catalyzed reactions between cyclic vinyloxiranes and dialkylzinc reagents was noted by Feringa et al. [51]. The 2,2 -binaphthyl phosphorus amidite ligands 32 and 43 (Fig. 8.5), which have been successfully used in copper-catalyzed enantioselective conjugate additions to enones [37], allowed kinetic resolution of racemic cyclic vinyloxiranes (Scheme 8.26). 

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. 

The salt precursor was prepared according to the following route as shown in Scheme 4. The desired enantiopure binaphthyl compound (5)-4 was made from 2-methyhiaphtalene (3) over five steps, which also included a resolution step [31-33]. The final precursor (5)-5 was obtained in 41% yield via a deprotonation of (5)-4 followed by the reaction with methyltrimethoxysilane and a subsequent reduction. 

Racemic modifications may be resolved. There are very few examples of this approach having been employed successfully. The racemic cylic ether (RS)-36, which contains two CH2OCH2CO2H arms attached to the 3 and 3 positions on the axially chiral binaphthyl units, has been resolved (48-50, 93, 94) to optical purity in both its enantiomers by liquid-liquid chromatography using a chiral stationary phase of either (R)- or (S)-valine adsorbed on diatomaceous eaitii. Very recently, the optical resolution of crown ethers (/ S)-37 and (/ 5)-38, incorporating the elements of planar chirality in the form of a rron -doubly bridged ethylene unit, has been achieved (95) by HPLC on (+)-poly(triphenyl-methyl methacrylate). 

Oxidative kinetic resolution of secondary alcohols mediated with a catalytic amount of optically active binaphthyl-type iV-oxyl has been performed with high selectivity". Also, it has mediated oxidative asymmetric desymmetrization of primary alcohols with good selectivity (equation 25)". ... 

CL Cooper, JB Davis, MJ Sepaniak. Mechanisms of enantiomeric resolution in cyclodextrin-modified capillary electrophoretic separations of binaphthyl compounds. Chirality 7 401-408, 1995. 

Wijnberg 86) separated several heterohelicenes on aluminium oxide coated with TAPA. The resolution factors are comparable with those of TAPA on silicagel they ranged from r = 1.12 for [7J-BOBBBOB to 1.20 for hexahelicene and some thiahexahelicenes. Other chiral selectors have been tested as to their usefulness for the resolution of helicenes. Binaphthyl-2,2 -diylhydrogenphosphate (BPA) (80) raised great expectations 88) because its chirality is of the same kind as that of... 

Figure 28. Principle of the resolution of the dicopper(I) molecular trefoil knot Cu2(K-84) +. The chiral auxiliary used is S-(+)-l,l -binaphthyl-2,2 -diyl phosphate (BNP-).

Optically active catalyst 1 can be obtained either by enantiomer-selective reaction of rac.-2 with optically active lithium (l,l -binaphthyl)-2,2 -diolate or by direct resolution by chiral HPLC. Optically active 21 and 22 in addition to 1 were successfully obtained by HPLC resolution and used for the polymerization of 1,5-hexadiene [60-62], Both catalysts gave an optically active polymer through cyclopolymerization. The optical activity and the content of tranj-structure in the main chain of the polymers obtained with 21 and 22 were comparable with those of the polymers synthesized with 1 [61,62],... 

Approaches using chiral starting material are found in Schemes 18, 20, 25, and 26, Equations (26) and (36)—(39), and reference <2001TL3307> in Section 13.03.9.2. The easily accessible chiral starting materials were obtained such as by dihydroxylation, from sugar derivatives, or from known binaphthyls. Approach by resolution of racemic thiepines is found in Schemes 24 and 26. Enantioselective transformation of thiaoxa[3.2.1]bicycles to tetrahydrothiepines by chiral base was also reported <1997JOC7080> (Section 13.03.9.2). 

This compound, in common with other suitable substituted biphenyls, possesses a chiral axis (p. 6) and is isolated from the reaction as a racemate. Although several resolution procedures have been reported, the superior method to date4 is that in which the binaphthol is first converted by treatment with phosphorus oxychloride into the binaphthyl phosphoric acid (14). Resolution is then effected by formation of diastereoisomeric salts with (+ )-cinchonine, appropriate fractional crystallisation and recovery of the (S)-( + )-binaphthyl phosphoric acid. Suitable hydrolysis gives (S)-( — )-l,l -bi-2-naphthol (15). 

We have investigated various factors which contribute to solvent-induced partial resolution or race-mization of 1,1 -binaphthyl (BN). Only photochemical interconversions of BN conducted in cholesteric mesophases influenced the steady state concentration of atropisomers. Thermal equilibriun in cholesteric media or photochemical interconver-sions in chiral isotropic solvents did not alter appreciably the atropisomeric ratio of initially racemic BN. Solvent order accelerates the rate of BN thermal racemization. A discussion of the physical properties of the solvents and BN responsible for the observations is presented. 

Jeong, Kim et al. reported use of the chiral DMAP derivative 22e, which was synthesized from 3-amino-DMAP, Kemp s triacid, and N-acetyl-2,2 -diamino-l,l -binaphthyl [26], As summarized in Scheme 12.11, selectivity factors up to 21 were observed with 1 mol% modular catalyst 22e in the kinetic resolution of a variety of secondary alcohols with acetic anhydride in tert-amyl alcohol as solvent, conditions first described by Fu et al. [20]. 

Data from the literature show that even if new convenient preparative methods are being developed for the resolution of l,l/-binaphthyl-2,2/-diol (17) via a phosphite using (—)-menthol as a resolving agent [39], the inclusion complexation method can still compete with these, owing to its simplicity, efficiency, and low cost. 

Among the preparative methods used for obtaining P-chiral phosphorus compounds, there are procedures involving the use of optically pure auxiliaries like (—)-menthol [40], (—)-ephedrin [41,42], or more recently, the kinetic resolution of 1-hydroxymethylalkylphenylphosphine oxides using Pseudomonas or Candida antarctica lipases [43], It has been found that some [(alkyl-substituted)arene] phosphinates and phosphine oxides can also be resolved efficiently by inclusion complexation with optically active 2,2 -dihydroxy-1, 1 -binaphthyl (17) [44],... 

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