Phase binaphthyl derivatives

Crown ether binaphthyl derivatives 128-131 (Scheme 71) were synthesized and investigated by Akagi [139], Compounds 128-131 were used to induce chiral nematic phases (N ) in liquid crystals. It was found that the helical twisting power increased with decreasing ring size. Helical polyacetylenes were synthesized in the N phases. It was found that the interdistance between the fibril bundles of the helical polyacetylene was equal to the half-helical pitch of the N liquid... 

Currently, the chiral phase-transfer catalyst category remains dominated by cinchona alkaloid-derived quaternary ammonium salts that provide impressive enantioselec-tivity for a range of asymmetric reactions (see Chapter 1 to 4). In addition, Maruoka s binaphthyl-derived spiro ammonium salt provides the best results for a variety of asymmetric reactions (see Chapters 5 and 6). Recently, some other quaternary ammonium salts, including Shibasaki s two-center catalyst, have demonstrated promising results in asymmetric syntheses (see Chapter 6), while chiral crown ethers and other organocatalysts, including TADDOL or NOBIN, have also found important places within the chiral phase-transfer catalyst list (see Chapter 8). 

The best selectivity in the Michael addition of 2-carboxycyclopentanones to an enone or enal were recently achieved by Maruoka et al. [9]. As shown in Scheme 4.5, as little as 2 mol% of the binaphthyl-derived phase-transfer catalyst 10 - in the presence of 10 mol% solid potassium carbonate - enabled the highly efficient... 

Oxidation of alcohols to carbonyl compounds using the stable nitroxyl radical TEMPO (41) as catalyst is a well-known preparative method [42, 43], Hypochlorite or peracetic acid is usually used as the final oxidizing agent and ca. 1 mol% of the catalyst 41 is used. In 1996 Rychnovsky et al. reported the synthesis of the chiral, binaphthyl-derived TEMPO analog 42 [44]. Table 12.1 lists the results obtained with 0.5-1 mol% of catalyst 42 [44], In these oxidation reactions 0.6-0.7 equivalents of sodium hypochlorite were used as the final oxidizing agent (plus 0.1 equiv. potassium bromide) in a two-phase system containing substrate and catalyst 42 in dichloromethane at 0 °C. As shown, the best selectivity factors (> 5) were observed for 1-phenylethanol and its derivatives as substrates. 

Analytical Properties CSP (chiral stationary phase) 1 — separates some chiral binaphthyl derivatives when mixtures of hexane diethyl ether, dichloromethane, or dioxane are used as the mobile phase CSP 2 — separates compounds with carbamate or amide functions (mixtures of n-hexane and 2-propanol can be used as mobile phase) CSP 3 — separation of compounds separated by CSP 2, as well as separation of compounds with carbonyl or amide functions and some amino alcohols that have pharmaceutical relevance ((3-blockers)... 

Chiral crown-ethers were originally developed to be used as chiral carriers in enantios-elective liquid-liquid extraction and/or as chiral phase transfer catalysts. The principle of stereoselective host-guest complexation with a chiral crown-ether type host and its application to LC has been first described in 1978 by Cram and co-workers [ 12. Currently, crown-ether type CSPs. which incorporate atropisomeric binaphthyl derivatives as chiral units incorporated in a 18-crown-6 type backbone with substituents that enforce discrimination between enantiomers are commercially available as Crownpak CR (-I-) and (—) (Daicel Chemical Ind.) (see Fig. 9.23a). 

The same kind of associative event lies at the heart of the catalytic asymmetric epoxidation of enones using the interesting binaphthyl derived spiro ammonium salt 33, which serves as a phase transfer catalyst as well as chiral auxiliary. Using sodium hypochlorite in a biphasic system, this catalyst mediates the high-yielding epoxidation of a variety of electron-deficient trisubstituted and trara-disubstituted olefins with excellent enantioselectivity, as represented by the conversion of enone 34 to the corresponding epoxy ketone 35 <04JA6844>. 

Noncoplanar aromatic monomers, such as 2,2 -disubstituted biphenylene derivatives and 4,4 -functionalized 1,1 -binaphthyl derivatives (Fig. 14) have been used as comonomers in para-linked aromatic polyesters with remarkable effects on the phase transition temperatures, the crystallinity, and the solubility. The incorporation of these noncoplanar monomers will not initially reduce the chain stiffness. The phenyl rings are forced by the 2,2 -substitution into a noncoplanar conformation which strongly decreases the intermolecular inter-... 

Apart from the HTP tuning for phase transition and color change, a binaphthyl-derived diarylethene dopant was demonstrated inducing the handedness inversion behavior by Akagi et al. [119]. (R)-26 with two un-bridged binapthyls can induce a right-handed CLC at its open form, while could be switched to left-handed upon... 

Hinze was the first to investigate the capabilities of micellar bile salt mobile phases [11, 12]. He found that a significant amount ( 5% v/v) of a long chain n-alcohol (pentanol, hexanol or heptanol) was useful to minimize the bile salt adsorption on the C18 stationary plmse. A wide range of solutes could be separated by these phases, PAHs, quinones, steroids, indoles, polar and lipophilic vitamins. These phases were also able to resolve optically big enantiomers such as binaphthyl derivatives [12]. Such compounds are... 

By virtue of the high helical twisting power and liquid crystallinity of the novel tetra-substituted binaphthyl derivative (D-2), we obtain a N -LC with a helical pitch in the nanoregime. This is performed by adding a high mole percentage of chiral dopant to the N-LC without destroying the LC phase. 

N -LC phase with the latter approach. Axially asymmetric chiral binaphthyl derivatives are known to have a larger twisting power than chiral compounds with an asymmetric carbon center [161, 162]. For our studies, we synthesized chiral (/ )- and (5)-PCH506-Binol from the optically active (R) (+) and (5) ( ) l,l -bi-2-naphtols by Williamson etherification reaction with a liquid crystalline phenylcyclohexyl (PCH) derivative (Fig. 9.34). The terminal alkyl chain was n-pentane, and the mesogen was linked to the binaphthyl with a hexamethylene spacer via ether bonds. 

The circular dichroism (CD) spectra of H-PAs that were synthesized in the (R)-N -LC phase show an absorption of 450-800 nm, corresponding to the PA chain K-K transitions and a positive cotton effect and vice versa. This suggests that the PA chain itself is twisted in one direction. It should be noted that the cotton effect is not due to the binaphthyl derivatives, which only show a cotton effect in the short wavelength range of 240-340 nm, which is different from the absorption region of... 

Light-induced LC phase changes were also observed for a bisbenzothienylethene derivative with cholesterol units and a chiral binaphthyl derivative with two diarylethene moieties. ... 

The Maruoka group s further efforts toward simplification of the catalyst have led to the design of new, polyamine-based chiral phase-transfer catalysts of type 15, with expectation of the multiplier effect of chiral auxiliaries, as illustrated in Scheme 5.10 [13]. The chiral efficiency of such polyamine-based chiral phase-transfer catalysts (S)-15 was examined by carrying out an asymmetric alkylation of glycine derivative 2 under phase-transfer conditions. Among various commercially available polyamines, spermidine- and spermine-based polyammonium salts were found to show moderate enantioselectivity. In particular, the introduction of a 3,4,5-trifluor-ophenyl group at the 3,3 -positions of chiral binaphthyl moieties showed excellent asymmetric induction. 

Other miscellaneous cyclization reactions leading to interesting thiophene derivatives include a thermal conversion of a 2,2 -bis(A/,Af-dimethylthiocarbamoyloxy)-1,1 -binaphthyl into a dinaphtho[2,l-6 l, 2 -t/ thiophene (a heterohelicene) <0581109>, solution-phase parallel synthesis of a 1140-member ureidothiophene earboxylic acid hbrary <05JCC253>, and an unexpected cyclization occurring upon metalation of diphenylsulfone, followed by introduction of (-)-fenchone and subsequent aqueous workup <05T10449>. Heating of the... 

The asymmetric synthesis of a-alkyl-a-amino acids using a chiral catalyst is a useful method for the preparation of both natural and unnatural amino acids. O Donnell et al. developed the cinchona alkaloid-catalyzed alkylation of glycine derivatives [49]. However, almost all of the chiral phase-transfer catalysts were restricted to cinchona alkaloid derivatives. In 1999, Maruoka and co-workers designed a chiral ammonium salt bearing a binaphthyl backbone as a chiral phase-transfer catalyst (10a) (Figure 10.11), and demonstrated its catalytic activity... 

The enantioselective alkylation of A-protected a-amino esters has been studied with many chiral catalysts, including spirocyclic ammonium salt 10A, while (lOB) containing two binaphthyl components is an effective mediator for alkylation of protected glycine under phase-transfer conditions.p-f-Boc-amino acid derivatized with (-l-)-pseu-doephedrine enables enantioselective alkylation of the ensuing amides. - Note the enolate derived from 11 remains chiral, alkylation products are produced in high ee. ... 

Toda procedure for obtaining enantiomeri-cally pure compounds will find broad application very soon. This development could make preparative HPLC with chiral columns obsolete and be applied to distillable amino acid derivatives as well. After all, analytical resolution of amino acids was quite successful by host/guest complexation chromatography with reversed-phase packings loaded with Cram s chiral 1,1 -binaphthyl crown ethers (similar to 1). [20]... 

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