Binaphthyl ether

In the synthesis of the swivel-cruciform binaphthyl-based oligomers 27 and 28, bromination of commercially available l,l -binaphthol followed by a Williamson reaction gives binaphthyl ethers with various alkoxy groups [43], The dibromi-... 

In addition to this enhancement, several other effects can be induced by the new conformation at the microscopic scale, such as the appearance of olf-diagonal molecular hyperpolarizability tensor components. The study of these microscopically aligned molecules has also provided new fundamental insights and was only made possible through creative synthetic chemistry. The systems that have been studied so far include dimers and tetramers such as the binaphthyl ethers and the calixarenes, and polymers with rigid backbones that force the pendant D ti-A chromophores into a non-centrosymmetric conformation. 

Figure 4. Structural formula and simplified geometry of a binaphthyl ether derivative. A is an electron acceptor. In the simplified geometry, is in a plane parallel to the AZ-plane.

This type of carbanion rearrangement is recognised to proceed by means of a radical dissociation-recombination mechanism. In 1983, Mazaleyrat and Wel-vart reported the kinetic resolution of a racemic binaphthyl ether, which involves an enantioselective variant of the [1,2]-Wittig rearrangement [Eq.(2)j [3]. 

The reaction of binaphthyl ether rac-2 with n-BuLi and a chiral coordinating agent, (-)-sparteine (l),gave the rearrangement product (+)-3 [enriched in (S)-axial chirality] and pentahehcene (-i-)-4, along with the recovered ether R)-2 in an enantioenriched form (28% optical purity). This result reveals that S)-2 rearranges faster than (R)-2 in the presence of (-)-l. 

In the case of binaphthyl ether 263, the secondary C—O bonds were hydrogenolyzed exclusively to provide the desired binaphthyl diol 264 (Scheme 81). ""... 

An aryne-based Diels-Alder reaction between tetrabromobiphenyl ether 169 and the dienolate anion generated from a,P-unsaturated amide 170 has been reported by Ruchirawat et al. in the synthesis of diospyrol derivatives, where the biphenyl ether 169 was converted to binaphthyl ether 171 in the presence of the sterically hindered base LiTMP (Scheme 12.49) [92],... 

Liquid crystals exhibit a partially ordered state (anisotropic) which falls in-between the completely ordered solid state and completely disordered liquid state. It is sometimes referred to as the fourth state of matter . In recent years, interest in liquid crystalline thermosets (especially liquid crystalline epoxy) has increased tremendously [33-44]. If the liquid crystal epoxy is cured in the mesophase, the liquid crystalline superstructure is fixed permanently in the polymer network, even at higher temperature. Liquid crystal epoxies are prepared using a liquid crystal monomer [33-38] or by chemical modification of epoxy resin [43] which incorporates liquid crystal unit in the epoxy structure. Liquid crystalline epoxy resins with different types of mesogen such as benzaldehyde azine [33], binaphthyl ether [34, 35], phenyl ester [36, 37] and azomethine ethers [38, 39] have been reported. Depending on the chemical nature of the mesogen, the related epoxies display a wide range of thermomechanical properties. The resins can be cured chemically with an acid or amine [40, 41] or by photochemical curing in the presence of a photo-initiator [3]. Broer and co-workers [42] demonstrated the fabrication of uniaxially oriented nematic networks from a diepoxy monomer in the presence of a photo-initiator. 

Not long thereafter, Tarnowski and Cram reported the first example of a hinged bis-crown ether. The compound was prepared in the usual Williamson reaction by heating a mixture of 2,2, 3,3 -tetrahydroxy-l, r-binaphthyl with pentaethylene glycol ditosylate and KOH in aqueous THF solution. The product (mp 159.5—161°) shown in Eq. (3.30) was obtained in 30% yield. This compound was shown to complex bis-ammonium cations of several varieties . 

The six-position may be functionalized by electrophilic aromatic substitution. Either bromination (Br2/CH2Cl2/-5°) acetylation (acetyl chloride, aluminum chloride, nitrobenzene) " or chloromethylation (chloromethyl methyl ether, stannic chloride, -60°) " affords the 6,6 -disubstituted product. It should also be noted that treatment of the acetyl derivative with KOBr in THF affords the carboxylic acid in 84% yield. The brominated crown may then be metallated (n-BuLi) and treated with an electrophile to form a chain-extender. To this end, Cram has utilized both ethylene oxide " and dichlorodimethyl-silane in the conversion of bis-binaphthyl crowns into polymer-bound resolving agents. The acetylation/oxidation sequence is illustrated in Eq. (3.54). 

The principal variations on the normal crown synthesis methods were applied in preparing mixed crowns such as those shown in Eq. (3.55) and in forming isomers of the dibinaphthyl-22-crown-6 systems. The latter has been discussed in Sect. 3.5 (see Eq. 3.21) . The binaphthyl unit was prepared to receive a non-naphthyl unit as shown in Eq. (3.57). Binaphthol was allowed to react with the tetrahydropyranyl ether or 2-chloroethoxyethanol. Cleavage of the THP protecting group followed by tosyla-tion of the free hydroxyl afforded a two-armed binaphthyl unit which could serve as an electrophile in the cyclization with catechol. Obviously, the reaction could be accomplished in the opposite direction, beginning with catechol". ... 

Armstrong and Jin [15] reported the separation of several hydrophobic isomers (including (l-ferrocenylethyl)thiophenol, 1 -benzylnornicotine, mephenytoin and disopyramide) by cyclodextrins as chiral selectors. A wide variety of crown ethers have been synthesized for application in enantioselective liquid membrane separation, such as binaphthyl-, biphenanthryl-, helicene-, tetrahydrofuran and cyclohex-anediol-based crown ethers [16-20]. Brice and Pirkle [7] give a comprehensive overview of the characteristics and performance of the various crown ethers used as chiral selectors in liquid membrane separation. 

Regarding bis-NHC chelating ligands, several structures that differ in the motifs used for the enlargement of the tether have been proposed as catalysts for the Mizoroki-Heck reaction. They range from non-functionalised aliphatic chains [23-25] to phenyl [26], biphenyl [27], binaphthyls [28] and to chains containing additional coordination positions like ethers [29], amines [30], and pyridines in an evolution towards pincer complexes [31-35], In most cases, the activity of aryl bromides in Mizoroki-Heck transformations was demonstrated to be from moderate to high, while the activation of chlorides was non-existent or poor (Scheme 6.7). 

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...

In comparison to the N- and S-counterparts, alkoxides possess lower nucleophilicity. Therefore, the reductive elimination process to form the C—O bond is much slower than those to form C— N and C—S bonds [103]. Palucki, Wolfe and Buchwald developed the first intramolecular Pd-catalyzed synthesis of cyclic aryl ethers from o-haloaryl-substituted alcohols [104]. For example, 3-(2-bromophenyl)-2-methyl-2-butanol (91) was converted to 2,2-dimethylchroman (92) under the agency of catalytic Pd(OAc)2 in the presence (S)-(-)-2,2 -bis(di-p-tolylphosphino)-l,r-binaphthyl (Tol-BINAP) as the ligand and K2CO3 as the base. The method worked well for the tertiary alcohols, moderately weE for cychc secondary alcohols, but not for acyclic secondary alcohols. 

E. Ishow, A. Credi, V. Balzani, F. Spadola, L. Mandolini, A Molecular-level Plug/socket System. Electronic Energy Transfer from a Binaphthyl Unit Incorporated into a Crown Ether to an Anthracenyl Unit Linked to an Ammonium Ion , Chem. Eur. ]. 1999, 5, 984-989. 

Now the interesting question arose of whether the intermediate analogous to 215 but devoid of the methyl groups, that is, 3d2-l H-naphthalene (221), would also be interceptable, because 221 should show a high thermodynamic acidity owing to its conversion into the 2-naphthyl anion (224) on deprotonation and because of the use of the strong base KOtBu for the liberation of 221 from 3-bromo-l, 2-dihydro-naphthalene (220) (Scheme 6.52). In the event, the major product was indeed naphthalene. However, there were further products, namely the enol ether 223 and small quantities of 2,2 -binaphthyl (228) as well as 1,2-dihydronaphthalene (226). The overall yield amounted to 92% [137]. 

The influence of additional functional groups on the complexing abilities of 1,3-xyly 1-crown ethers [28] and [50]—[53] and binaphthyl-crown ethers... 

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). 

The monobenzhydiyl derivative of (S)-binaphthol has played an important role, not only in the synthesis of chiral bisbinaphthyl crown ether derivatives, for example, (55)-124, containing two different bridges between the two binaphthyl units, but also in the provision of an entry into the constimtionally isomeric derivative (5S)-125. Rational stepwise syntheses of macrocyles containing three binaphthyl units have been devised and applied to the synthesis of (SSS)-126 and (RSS)-127. Cleariy, in all these procedures, the C2 symmetry of the chiral building block restricts the number of products (to one ) and defines the symmetries of the macrocycles formed. 

Prelog and co-workers (160, 161) chose 9,9 -spirobifluorene as a starting material for synthesizing chiral crown ethers since (i) it has a more rigid carbon skeleton than the 1,1 -binaphthyl unit, and (ii) it can be substituted easily in the 2 and 2 positions by electrophilic reagents. Thus, the 2,2 -diacetyl derivative (Figure 19) obtained after a Friedel-Crafts on 9,9 -spirobifluoiene can be con-... 

Although a large number of biscrown ethers based on the binaphthyl nucleus have been synthesized (157) many of these have only been isolated and characterized as their racemic modifications. An exception is provided (157) by (SS)-152, obtained from the chiral bisbinaphthyl-22-crown-6 derivative in which one of the binaphthyl units carries chloromethyl groups (in the 3 and 3 positions) capable of reacting, in the presence of base, with tetraethylene glycol. 

One example involves the addition of stannyl enol ethers to benzaldehyde in the presence of silver triflate and the chiral 2,2,-bis(diphenylphosphino)-l,l/-binaphthyl... 

The conjugation in the molecular wire may be disrupted or modulated to create systems with different properties. For example, a porphyrin Ceo donor-acceptor system linked with a conjugated binaphthyl unit, has a preference for the atropi-somer where the fullerene unit is closer to the porphyrin system, thus increasing the through space interactions [82]. The charge transfer process on a dyad containing a crown ether in the linker structure can be modulated by complexation/ decomplexation of sodium cations [83] but even more interesting is the construction of supramolecular systems where the donor and acceptor moieties are... 

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