2.2 -Dihydroxy binaphthyl derivatives

In this reaction, 2,2 -dihydroxy binaphthyl derivatives (BINOLs) are used together with Ti(OP-i)4 complex. The highly polarized C=0 of the formyl group having a 5+ at the carbon atom is attacked by the most electron-abundant para position of N,N-dimethylanilines from a less sterically hindered direction (re) to give the product with an (R)-configuration 29. 

Tanaka, K., Moriyama, A., and Toda, F. (1997) Novel Chiral Recognition in Host-Guest Inclusion Complexes Depending on Their Molar Ratios Efficient Resolution of 2,2 -Dihydroxy-1,1 -binaphthyl Derivatives and CD Spectral Study of Inclusion Complex Crystals, J. Org. Chem., 62, 1192-1193. 

The chemical compounds, (i )- and (5)-2,2-dihydroxy-1,1-binaphthyl (optical purity, 0.99), are purchased from commercially available sources. The di-substituted binaphthyl derivatives, (i )- and (iS)-l,T-binaphthyl-2,2 -di-[par<2-(zr<2 .s-4- -pentylcyclohexyl)phenoxy-1 -hexyl]ether, are synthesized through the Williamson etherification reactions of chiroptical (i )-(- -)- and (pentyl group (the number of carbon of 5), and hexamethylene chain linked with an ether-type oxygen atom, [-(CH2)60-, 06], and thus abbreviated as PCH506. 

Toda, F., and Tanaka, K. (1997) New Chiral Ammonium Salt Hosts Derived from Amino Acids Very Efficient Optical Resolution of 2,2 -Dihydroxy-l,r-binaphthyl by Complexation with These Host Compounds, Chem. Commun., 1087-1088. 

Pioneering studies by Cram and co-workers employed crown ether arrays 35a-c incorporating a 2,2 -dihydroxy-l,l -binaphthyl unit as the chiral barrier <1975PAC327>. Enhancements in the chiral recognition of amino acids were obtained by placing large substituents, at the 3,3 -positions of the binaphthyl moiety, so as to raise its steric barrier. 3,3 -Diphenyl derivative 35c is often the benchmark to which other chiral crown ethers are compared <1981JOC393>. 

In 1951 Bothner-By first attempted asymmetric reductions based on the conversion of lithium aluminum hydride (LAH) into a chiral alkoxy derivative by reaction with (+)-camphor. Since this pioneering work, the use of chirally modified LAH reagents has been the focus of much attention. In 1979, the first virtually complete enantiofacial recognition of prochiral carbonyl compounds was accomplished by using LAH modified with optically pure 2,2 -dihydroxy-1,1 -binaphthyl and a simple alcohol (BINAL-H). Asymmetric reduction with chiral 2,5-dimethylborolane also gave alcohols in high optical yields." Recently, excellent results have been obtained using a chirally modified sodium borohydride... 

Metal phenoxides are utilized extensively in organic synthesis as reagents, since they can readily be prepared from phenols and appropriate metal reagents, and the phenol moiety can easily be modified either sterically or electronically. Particularly, 2,2 -dihydroxy-l,l -binaphthyl (BINOL), salicylideneamine and Af,Af -ethylenebis(salicylideneamine) (salen) proved to be excellent phenol ligands for asymmetric synthesis. Since some of their reactions have recently been reviewed , it may not be appropriate to reproduce all of them. Instead, this section concentrates on the effect of the phenol moiety on the chemical reactivity and selectivity, and tries to provide structure-activity relationships for the metal phenoxide reagents. Metalated derivatives of monophenols, biphenols and salicylaldehyde imines are discussed separately. 

For the 3,3 -dimethyl derivative 8, several other methods have been developed. The racemic 3,3 -dimethy] compound can be prepared by aminomcthylation of binaphthol with subsequent conversion of the aminomethy] function to a methyl group, and resolved analogously to binaphthol via the phosphoric acid derivative15. Another possibility is the preparation [oxidation of 3-hydroxy-2-naphthoic acid with iron(III) chloride] and resolution [with (S)-leucine methyl ester] of 2,2 -dihydroxy-1,l -binaphthyl-3,3 -dicarboxylic acid (7). 

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... 

Before synthetic chiral stationary phases were developed, attempts were made to use naturally occurring chiral materials for the stationary phase. Quartz, wool, lactose and starch were inadequate but triacetylated cellulose has met with some success. The synthetic stationary phases introduced by Pirkle are able to interact with solute enantiomers in three ways, one of which is stereochemically dependent. Typically these interactions are based on hydrogen bonding, charge transfer (rc-donoi -acceptor based) and steric repulsive types. An independent chiral stationary phase therefore consists of chiral molecules each with three sites of interaction bound to a silica (or other) support. Early work in this area demonstrated that 5-arginine bound to Sephadex would resolve 3,4-dihydroxy-phenylalanine, and that direct resolution of chiral helicenes could be accomplished with columns packed with 2-(2,4,5,7-tetranitro-9-fluorenylideneaminoxy)-propionamide or tri-P-naphthol-diphosphate amide. Amino acid esters have also been resolved with a silica bound chiral binaphthyl crown ether, but better separations are achieved with A-acylated amino acid derivatives with amino-acid derived chiral stationary phases. 

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