Binaphthol naphthol

Kobayashi et al. have reported the use of a chiral lanthanide(III) catalyst for the Diels-Alder reaction [51] (Scheme 1.63, Table 1.26). Catalyst 33 was prepared from bi-naphthol, lanthanide triflate, and ds-l,2,6-trimethylpiperidine (Scheme 1.62). When the chiral catalyst prepared from ytterbium triflate (Yb(OTf)3) and the lithium or sodium salt of binaphthol was used, less than 10% ee was obtained, so the amine exerts a great effect on the enantioselectivity. After extensive screening of amines, ds-1,2,6-... 

In recent years, axially chiral binaphthalene derivatives have emerged as important ligands and chiraUty inducers in organic synthesis. Oxidative coupling of 2-naphthols represents a well estabhshed method for the preparation of binaphthols. The couplings are usually carried out by treating naphthols with more than an equimolar amount of a metal such as Fe(III), Mn(III),... 

Nakajima et al. (128) found that a number of diamines functioned as moderately effective ligands for Cu(II) in the catalytic aerobic oxidation of 2-naphthols. A series of proline derivatives were evaluated with the aniline ligand 187 providing optimal selectivities. Unfortunately, 2-naphthol affords only racemic binaphthol. With an isolated catalyst, formulated as 187 Cu(OH)Cl in analogy to the known TMEDA Cu(OH)Cl (TMEDA = A,A,A,A-tetramethylethylenediamine), oxidative... 

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]. 

Only a few efforts have been made to evaluate the effects of TA structural variations on toxicity. Methylation decreases toxicity of hemigossypol to Verticillium dahliae (25), of gossypol to rat mast cells (23), and of various TA to HelionTis sod. (22). In contrast, methylaTTon increases the toxicity of various TA"To nematodes (26) and the toxicity of heliocides to rat mast cells ( ). The order of toxicity of different TA to rat mast cells is quinones > heliocides > naphthols > binaphthols (23). Gossypol generally is somewhat more toxic to insects than heliocides, and quinones are least toxic (29,22). 

With the bisoxazoline hgand (S)-Phbox and CuCl, the asymmetric oxidative couphng of 2-naphthol and hydroxy-2-naphthoates resulted in an asymmetrically substituted 2,2 -binaphthol with ee s of up to 65% [260]. On the basis of the previous results obtained with this catalyst system, the asymmetric oxidative cross-coupling polymerization of 2,3-dihydroxynaphthalene [261] and methyl 6,6 -dihydroxy-2,2 -binaphthalene-7,7 -dicarboxylate [262] as well as the copolymerization of 6,6 -dihydroxy-2,2 -binaphthalene and dihexyl 6,6 -dihydroxy-2,2 -binaphthalene-7,7 -dicarboxylate with Cu diamine catalysts were carried out imder aerobic conditions, using O2 as the oxidant, and a cross-coupling selectivity of 99% was achieved [263]. 

The chiral ligand BINAP was originally prepared from 2,2 -binaphthol and resolved by complexation with an optically active Pd complex [ 10]. A new method starting from 2-naphthol was developed (Scheme 3.2) [11], In this method optical resolution was achieved at the stage of BINAP dioxide (BINAPO) by using inexpensive optically active acids such as camphorsul-fonic acid and dibenzoyltartaric acid. 

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). 

The quantum yields decreases by changing from planar naphtholes to the perpendicular binaphthole independent on the absence or presence of pyridine [162], Also, in the case of optical active l,T-binaphthyl-2,2 -diamine (BNA) compared with A-phenyl-p-naphthylamine (PNA), the quantum yield of electron transfer is for BNA by a factor of 0.5 lower due to the perpendicular structure [161]. A possible explanation is that the approach of the perpendicular donors BN(OH)2 and BNA to the almost spherical fullerenes is hindered, while the planar 2-NOH and PNA more easily contact with the fullerenes [161,162], The quantum yields of C70 in the absence of pyridine are slightly higher than those of C6o suggesting a slightly stronger acceptor ability of C70 [162],... 

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... 

The coupling of 2-naphthol to give 2,2 -binaphthol has served as a testing ground for many oxidation protocols. For example, binaphthol has been prepared using vanadium reagents... 

Titanium- and cerium-based reagents have been used to prepare binaphthol structures [95, 96]. Jiang showed that treatment of 2-naphthol (68a) with cerium(IV) ammonium nitrate (CAN) leads to the biaryl product 69a in yields of around 90 % (Scheme 32). Crosscoupling of differently substituted naphthols can be accomplished using the same reagents, albeit in lower yields. 

Zeolites (crystalline aluminosilicates) supporting oxidizing metals (Fe or Cu) have been introduced by Garcia and co-workers [106]. In particular, they showed that FeMCM-41 affords binaphthol from 2-naphthol as virtually the only product. Unfortunately, this compound is trapped in the zeolite pores and the isolated yields are lower than expected. 

The use of a chiral reagent for the oxidative coupling of naphthols has received much attention as the product chiral binaphthols are widely used in asymmetric synthesis [138]. The well-known oxidative coupling of 2-naphthol by dioxygen in the presence of a copper com-... 

In the same vein, Koslowski and co-workers have published a study using chiral 1,5-diazadecalin complex 225, a species that directs binaphthol formation with excellent enan-tioselectivity [149]. The use of Cul or Cu(OTf) as a copper source in this procedure contributes to the excellent yields (85 %) and high enantiomeric excesses ( 90 %) (Scheme 59). Substituents on the nitrogens of 225 or changes in the copper source resulted in lower yields and/or lower enantioselectivities. Other naphthol substrates have been subjected to these conditions, but both the yields and enantioselectivities were diminished, showing the importance of the ester moiety with regard to the efficiency of the reaction (Table 40). 

In 1979, Noyori and co-workers invented a new type of chiral aluminum hydride reagent (1), which is prepared in situ from LiAlEE, (S)-l, E-bi-2-naphthol (BINOL), and ethanol. The reagent, called binaphthol-modified lithium aluminum hydride (BINAL-H), affects asymmetric reduction of a variety of phenyl alkyl ketones to produce the alcohols 2 with very high to perfect levels of enantioselectivity when the alkyl groups are methyl or primary1 (Scheme 4.3a). 

Phenol coupling occurs chemically under oxidation with Fe(III). The most famous example is the coupling of 2-naphthol to give binaphthol—an ortho ortho coupling. The stereochemistry of binaphthyls like this was discussed in Chapter 45. 

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