Binaphthols, catalysis

Trilluoroacetaldehyde (fluoral) undergoes facile highly stereoselective condensation with silyl enol ethers under titanium(ll) chloride binaphthol catalysis to give 2. ... 

Over the last few years several examples have been reported in the field of asymmetric catalysis that are based on the interaction of two centers.6,119 Recently, Shibasaki and coworkers have developed an asymmetric two-center catalyst. Scheme 3.14 shows preparation of optically active La binaphthol (BINOL). This catalyst is effective in inducing the asymmetric nitro-aldol reaction, as shown in Scheme 3.15. 

Yamamoto et al. have reported the asymmetric catalysis of a chiral Lewis acid in a carbonyl-ene reaction, which uses chloral as the enophile and an aluminum catalyst with enantiopure 3,3 -bissilylated binaphthol (BINOL) to give the corresponding homoallylic alcohol with 78% ee in 79% yield (Scheme 8C.2) [6]. It should be noted that 3,3 -diphenyl-BINOL-derived aluminum catalyst provides the racemic product in low yield. 

The asymmetric oxidation of sulphides to chiral sulphoxides with t-butyl hydroperoxide is catalysed very effectively by a titanium complex, produced in situ from a titanium alkoxide and a chiral binaphthol, with enantioselectivities up to 96%342. The Sharpless oxidation of aryl cinnamyl selenides 217 gave a chiral 1-phenyl-2-propen-l-ol (218) via an asymmetric [2,3] sigmatropic shift (Scheme 4)343. For other titanium-catalysed epoxidations, see Section V.D.l on vanadium catalysis. 

K. Mikami, Y. Motoyama, and M. Terada, Asymmetric catalysis of Diels-Alder cycloadditions by an MS-free binaphthol-titanium complex dramatic effect of MS, linear vs positive nonlinear relationship and synthetic applications, J. Am. Chem. Soc., 116 (1994) 2812-2820. 

Modest enantioselectivity was observed for the P-replacement reaction catalyzed by 33-36 bilayer membranes [45]. D-Tryptophan formation prevailed over that of the l-form in 50-55 % ee regardless of chirality of the substrate, serine. Conversely, no enantioselectivity was observed when the 32 vesicle was used in place of 33. This suggested that the imidazolyl group of 33 might exercise stereospecific acid catalysis in the protonation of the prochiral carboanion intermediate. The enantioselectivity was also modest (ca. 30% ee) when the P-replacement reaction was mediated by the co-vesicle formed with 37,32, and an additional peptide lipid having (S)-binaphthol moieties (35) in the presence of Cu(n) ions. 

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. ... 

Chiral (helical) Lewis acids for asymmetric Diels-Alder catalysis are prepared from titanium tetraisopropoxide 5 and a chiral binaphthol ligand 4 [13]. The titanium reagent 6 plays an important role as chiral template for the fixation of a,fi-unsaturated aldehydes and thereby for the enantioface recognition of substrates. The asymmetric Diels-Alder reaction, e. g., of cyclopentadiene 7 and acrolein 8, is effected in the presence of catalytic (P)-6 (10 mol%), producing the endo adduct 9 (R =R2=H) in 88% ee (Scheme 1). 

Matsuoka, T., Harano, K., Uemura, T., Hisano, T. Hetero Diels-Alder reaction of N-acyl imines. I. The reaction of N -thiobenzoyl-N,N-dimethylformamidine with electron-deficient dienophiles. Stereochemical and mechanistic aspects. Chem. Pharm. Bull. 1993, 41, 50-54. Mikami, K., Motoyama, Y., Terada, M. Asymmetric Catalysis of Diels-Alder Cycloadditions by an MS-Free Binaphthol-Titanium Complex Dramatic Effect of MS, Linear vs Positive Nonlinear Relationship, and Synthetic Applications. J. Am. Chem. Soc. 1994, 116, 2812-2820. 

Yamago, S., Furukawa, M., Azuma, A., Yoshida, J.-i. Synthesis of optically active dendritic binaphthols and their metal complexes for asymmetric catalysis. Tetrahedron Lett. 1998, 39, 3783-3786. 

Aoki, S., Mikami, K., Terada, M., Nakai, T. Enantio- and diastereoselective catalysis of addition reaction of allylic silanes and stannanes to glyoxylates by binaphthol-derived titanium complex. Tetrahedron 1993, 49,1783-1792. 

Oguni has reported asymmetric amplification [12] ((-i-)-NLE) in an asymmetric carbonyl addition reaction of dialkylzinc reagents catalyzed by chiral ami-noalcohols such as l-piperidino-3,3-dimethyl-2-butanol (PDB) (Eq. (7.1)) [13]. Noyori et al. have reported a highly efficient aminoalcohol catalyst, 2S)-3-exo-(dimethylamino)isobomeol (DAIB) [14] and a beautiful investigation of asymmetric amplification in view of the stability and lower catalytic activity of the het-ero-chiral dimer of the zinc aminoalcohol catalyst than the homo-chiral dimer (Fig. 7-5). We have reported a positive non-linear effect in a carbonyl-ene reaction [15] with glyoxylate catalyzed by binaphthol (binol)-derived chiral titanium complex (Eq. (7.2)) [10]. Bolm has also reported (-i-)-NLE in the 1,4-addition reaction of dialkylzinc by the catalysis of nickel complex with pyridyl alcohols [16]. 

Building upon this earlier work, Kee and co-workers chose to move away from binaphthol as a chiral framework and explore alternative systems which may permit phospho-aldol catalysis under mild conditions but crucially be compatible with aerobic conditions. Their earliest studies revolved around the well-... 

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