Amino binaphthols

Cross-coupling reactions between amines and aryl halides or pseudohalides have been employed for the preparation of a number of chiral, nonracemic ligands for asymmetric catalysis. For example, early studies by Buchwald illustrated that chiral amino binaphthol derivatives could be generated by Pd-catalyzed Af-arylation of binaphthol-derived triflates (Eq. 74) [417]. A similar strategy was employed by Erase for the synthesis of planar-chiral [2.2]paracyclophane ligands (Eq. 75) [418]. The A -arylation of [2.2]paracyclophane-derived triflates has also been used for the construction of planar-chiral benzimidazoles [419]. The IV-arylation of a substituted pyrrolidine with 4-bromopyridine played a key role in the synthesis of a chiral nucleophilic catalyst related to DMAP [420]. 

The synthesis of a series of chiral organophosphine oxide/sulfide-substituted binaphtholate ligands has recently been reported by Marks and Yu and their corresponding lanthanide complexes characterized. These complexes, generated in situ from Ln[N(TMS)2]3, cleanly catalysed enantioselective intramolecular hydroamination/cyclisation of 1-amino-2,2-dimethyl-4-pentene albeit with a low enantioselectivity of 7% ee (Scheme 10.82). 

Cram and co-workers have experimented extensively with chiral recognition in crown ethers derived from various 3-binaphthols (73). In nonpolar solvents, these chiral ethers complex salts of PEA and various chiral a-amino esters (with fast exchange), inducing nonequivalence in their NMR spectra. The senses of proton nonequivalence induced in these solutes have been used to support proposed structures of the diastereomeric solvates (74). 

A variety of phenol couplings have been described. Those reported before 1991 have been reviewed [66]. 2-Naphthol (27) was oxidized to l,l -binaphthol (28) in high current efficiency on a graphite felt electrode coated with a thin poly(acrylic acid) layer immobilizing 4-amino-2,2, 6,6-tetramethylpiperidinyl-l-oxy (4-amino-TEMPO) (Scheme 10) [67]. 

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. 

The prototype of a first fluorescence sensor for enantioselective recognition of chiral amino alcohols was synthesised by Pu et al. by linking phenylacetylene dendrons to an axially chiral binaphthol core unit (see Fig. 4.71) [14c, d, 25],... 

For example, N-(2-hydroxyphenyl)imines 9 (R = alkyl, aryl) together with chiral zirconium catalysts generated in situ from binaphthol derived ligands were used for the asymmetric synthesis of a-amino nitriles [17], the diastereo- and/or enantioselective synthesis of homoallylic amines [18], the enantioselective synthesis of simple //-amino acid derivatives [19], the diastereo- and enantioselective preparation of a-hydroxy-//-amino acid derivatives [20] or aminoalkyl butenolides (aminoalkylation of triisopropylsilyloxyfurans, a vinylogous variant of the Mannich reaction) [21]. A good example for the potential of the general approach is the diastereo- and enantioselective synthesis of (2R,3S)-3-phenylisoserine hydrochloride (10)... 

Al complexes prepared in situ from Al[OCH(CH3)2]3 and two equivalents of (K)-BINAPHTHOL (9) and (i )-H8-BINAPHTHOL (10) promoted the enanti-oselective reduction of propiophenone with borane-dimethyl sulfide and gave the S alcohol in 83% and 90% ee, respectively (Scheme 7) [47]. The reaction was much slower and afforded a racemic product in the absence of Al[OCH(CH3)2]3 under otherwise identical conditions. The addition of a catalytic amount of Al(OC2H5)3 increased both the rate and enantioselectivity in the hydroboration of ketones with a chiral amino alcohol [48]. 

Chiral Ligand of LiAlH4 for the Enantioselective Reduction of a,p-Unsaturated Ketones. Enantioselective reductions of a,p-unsaturated ketones afford optically active ally lie alcohols which are useful intermediates in natural product synthesis. Enantioselective reduction of a,p-unsaturated ketones with LiAlH4 modified with chiral amino alcohol (1) affords optically active (S)-allylic alcohols with high ee s. When 2-cyclohexen-l-one is employed, (5)-2-cyclohexen-l-ol with 100% ee is obtained in 95% yield (eq 2). This is comparable with the results obtained using LiAlH4-chiral binaphthol and chiral 1,3,2-oxazaborolidine. ... 

The chiral-modified binaphthol complex (23) has been prepared (Eq. 10) and shown to be an efficient catalyst for enantioselective Memnich-type reactions [9]. The reaction of imine (24) with ketene silyl acetal in the presence of the catalyst 23 with NMI afforded /3-amino acid derivatives 25 and 26 in high enantioselectivity (Eq. 11). 

A mechanism has been proposed for the enantioselective Mikami ene reaction of a terminal alkene with a glyoxylic aldehyde using a chiral binaphthol as Lewis acid. Stereoselective synthesis of 5-amino esters via asymmetric aldol-type and aza-Diels-Alder reactions has been reviewed. Siliranes react cleanly with benzaldehyde to produce oxasilacyclopentanes—with inversion— under conditions of Bu OK catalysis enolizable aldehydes yield sdyl enol ethers. ... 

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. 

The efficient kinetic resolution of chiral aminoalkenes has been achieved utilizing the binaphtholate complexes (R) 38 Ln (Table 11.3) [52, 124]. Various chiral amino pentenes were kinetically resolved with resolution factors/(defined as f= x fefast/fesiow, where is the Curtin Hammett equilibrium constant between the two diastereomeric substrate/catalyst complexes and kfast/fesiow being the ratio between the faster and the slower reaction rate constant) as high as 19 and enantiomeric excess for recovered starting material reaching >80% ee at conversions dose to 50%. The... 

Titanium complexes that are similar to Duthaler s ( 2.5.2) can be generated from TiCl4, Ti(Or-Pr)4 and diacetoneglucose 1.48. These complexes catalyze asymmetric hetero-Diels-Alder reactions, and give high enantiomeric excesses [827], Corey and coworkers [828] also prepared a chiral titanium catalyst derived from cis-/V-sulfonyl-2-amino-1 -indanol and used this to catalyze asymmetric Diels-Alder reactions. Buchwald and coworkers [829, 830] have proposed the use of titanocene-binaphthol catalysts for asymmetric hydrogenation of imines or trisubsti-tuted olefins. 

As shown in Table 26, the same selectivities were observed in the reactions of other 3-acyl-l,3-oxazolidin-2-ones. Thus, by using the same chiral source ((R)-(+)-binaphthol), both enantiomers of the Diels-Alder adducts between 3-acyl-l,3-oxazolidin-2-ones and cyclopentadiene were prepared. Traditional methods have required both enantiomers of chiral sources in order to prepare both enantiomers stereoselectively [74], but the counterparts of some chiral sources are of poor quality or are hard to obtain (for example, sugars, amino acids, alkaloids, etc.). It is noted that the chiral catalysts with reverse enantiofacial selectivities could be prepared by using the same chiral source and a choice of achiral ligands. 

Reaction of yS-naphthol with yV,A -dimethylhydrazine under oxygen atmosphere and tungsten lamp irradiation leads via a radical process to the formation of l-amino-2-binaphthol in high yield (Scheme 29) [82]. This unique example of C-N bond for-... 

Carreira s recent work is an extension of earlier studies [5] in which a titanium(IV) complex, prepared in situ from tridentate ligand ( )-l and Ti(Ot Pr)4, was found to catalyze Mukaiyama aldol reactions with high enantioselectivities. The chiral ligand used in both the ene and aldol chemistry is prepared from 3-bromo-5-ferf-butylsalicylaldehyde and 2-amino-2 -hydroxy-l,T-binaphthol. This... 

Two types of strategy are used to obtain enantiopure MOCNs. The one employed most often consists of introducing the chiral information into the assembly ligand of the metallic ion network. The molecules most frequently used for this are binaphthol derivatives, tartrate ions, polypyridines substituted with chiral groups and amino acids. It is also possible to prefabricate a chiral building block of known configuration, the self-assembly of which leads to the desired MOCNs. 

When two aryllithium moieties are part of the same ethylenic substrate, representing a meso-diether, as in Scheme 43, the addition-elimination process (Sn2 reaction) can be directed by chiral ligands chiral amino alcoholates, or al-coholates derived from binaphthol promote the formation of one enantiomer of the resulting dihydrobenzofuran [70]. 

The well known chiral carbon skeleton designated as binaphthyl hinge has been introduced into asymmetric synthesis and resolution of racemates in the form of the derivatives of 2,2 -dihydroxy-l,r-binaphthyl (84, binaphthol). The application of chiral crown compounds containing this binaphthyl tmit for the separation of amino acids and amino acid esters by use of liquid/liquid chromatography has been described particularly by Cram et al. in detail... 

Shibasaki developed the first catalytic enantioselective hydropho-sphonylation of aldimines with the use of chiral heterobimetallic lantha-num(iii) potassium(i) tris(binaphtholate) 89, which provides optically active a-amino phosphonates with high enantioselectivities (Scheme 2.50). Similar to lithium catalyst 26 and sodium catalyst 67, potassium catalyst 89 acts as an acid-base bifunctional catalyst to activate both nucleophiles and electrophiles. In particular, in this reaction, deprotonation of dimethyl phosphite by more basic potassium catalyst 89 was essential for increasing the reactivity and enantioselectivity, while less basic lithium catalyst 26 and sodium catalyst 67 were not effective. 

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