Catalysts binaphthyl derivatives

In 1996 Yang and coworkers reported a series of binaphthyl-derived -symmetric ketones (8) as epoxidation catalysts (a few examples are shown in Fig. 2)[32-34],... 

In Ught of the recent developments in thiourea, diol, and phosphoric-acid-mediated catalysis, far fewer studies have focused on the use of chiral carboxyhc acids as suitable hydrogen bond donors. To this end, Mamoka synthesized binaphthyl-derived dicarboxylic acid 49 which catalyzes the asymmetric Mannich reaction of N-Boc aryl imines and tert-diazoacetate (Scheme 5.65) [120]. The authors postulate that catalytic achvity is enhanced by the presence of an addihonal car-boxyhc acid moiety given that use of 2-napthoic acid as catalyst provided only trace amounts of product... 

Connon and co-workers synthesized a small library of novel axially chiral binaphthyl-derived bis(thio)ureas 152-165 and elucidated the influence of the steric and electronic characteristics of both the chiral backbone and the achiral N-aryl(alkyl) substituents on catalyst efficiency and stereodifferentiation in the FC type additions of indole and N-methylindole to nitroalkenes (Figure 6.50) [315]. 

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 direct addition of in situ-prepared arylzinc to aldehydes with chiral binaphthyl-derived amino alcohols (24) as catalysts has afforded optically active diarylmethanols in high yields and with excellent enantioselectivities (up to 99% ee).106 By using a single catalyst, both enantiomers of many pharmaceutically interesting diarylmethanols can be obtained by the proper combination of various arylzinc reagents with different aldehydes. 

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... 

The binaphthyl-derived iminium-ion catalysts 41a and 41b were introduced by Aggarwal et al. [48a] and Page et al. [48b], respectively (Table 10.7). The highest enantioselectivities reported to date for an iminium-based olefin epoxidation -95% ee using 1-phenyl-3,4-dihydronaphthalene as substrate - were achieved with the catalyst 41b [48b]. 

The oxidation of alcohols to carbonyl compounds with the stable nitroxyl radical TEMPO (86) as catalyst is a well-known preparative method [134, 135]. Hypochlorite or peracetic acid is usually used as the final oxidizing agent and ca. 1 mol% of catalyst 86 is used. In 1996 Rychnovsky et al. reported the synthesis of the chiral, binaphthyl-derived TEMPO analog 87 [136], Results obtained by use of 0.5-1 mol% of catalyst 87 [136] are listed in Table 10.12. In these oxidation reactions 0.6-0.7 equiv. sodium hypochlorite were used as the final oxidizing agent (plus... 

Here R and S are the two enantiomeric forms of binaphthyl, C stands for the active sites on the carbon, C B is the catalyst-binaphthyl complex, I is an inhibitor and C I the inactive catalyst-inhibitor complex. On the assumption of steady state concentrations of C B and C I, Pincock et al. [39, 40] derived the equation... 

The amount of catalyst can be reduced to 5 mol % using the binaphthyl-derived Ti-com-plex 32 [11]. Only 2 mol% of Carreira s [12] catalyst 35 is necessary to obtain good yields and high ee values. However, the chiral binaphthyl ligand for 35 is not commercially available. 

The Buchwald group has reported that hindered binaphthyl-derived phosphine 28 is an effective supporting ligand for the coupling of aryl chlorides and phenols [ 152]. This catalyst system provided the desired ethers in good to excellent yield, Eq. (197). 

Enantiomeric purities ranging from 20 to 80% have been reported for the acid-promoted asymmetric oxidation of sulfides to sulfoxides by binaphthyl-derived oxaziridines has been described <2007T6232>. A novel amino hydroxylation of olefins has been developed using /ra t-2-phenylsulfonyl-3-phenyloxaziridine 33 <2007JA1866>. The reaction, which is catalyzed by copper(ll) salts, affords good yields of the product. Oxidation of aldimines to oxaziridines using alumina-supported M0O3 catalyst and anhydrous /-butyl hydroperoxide (TBHP) has been described. Yields are excellent. 

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 VCD study of the 1,1 -binaphthyl derivatives [110] serves as an example of other structural information that can be obtained by the comparison of experimental and computed VCD. This method allows monitoring not only of absolute chirality of the molecule, but also of the contributions of individual functional groups to the spectra, molecular conformations or some important structural parameter. As an example, we discuss chiral binaphthyls which represent popular building blocks, chiral recognition receptors and catalyst. Controlling the angle between naphthyl planes is important when supramolecular complexes based on these compounds are built. 

Naruta et al. [225, 226] designed the twin-coronet porphyrin ligands (62) and (63) with binaphthyl derivatives as chiral substituents (Figure 13). Each face of the macrocycle is occupied by two binaphthyl units and the ligand has C2 symmetry. Iron complexes of these compounds can be very effective catalysts in the epoxidation of electron-deficient alkenes. Thus, nitro-substituted styrenes are readily epoxidized in 76-96% ee [226]. The degree of enantioselectivity can be explained on the basis of electronic interactions between the substrate aromatic ring and the chiral substituents rather than on the basis of steric interactions. 

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>. 

An axially chiral and highly hindered binaphthyl-derived guanidine catalyst 18a with an internal guanidine unit (Figure 4.6) facilitates the highly enantioselective 1,4-addition... 

FIGURE 3.3 Construction of asymmetric reaction field for acetylene polymerization by dissolving Ziegler-Natta catalyst, Ti(0-n-Bu)4-AlEt3, into the chiral nematic LC. The chiral nematic LC includes an axially chiral binaphthyl derivative or an asymmetric center containing chiral compound. 

Helical polyacetylene was synthesized in asymmetric reaction field consisting of chiral nematic LC. The chiral nematic LC was prepared by adding a chiroptical binaphthyl derivative as a chiral dopant to a mixture of two nematic LCs. Acetylene polymerizations were carried out using the catalyst Ti(0-n-Bu)4— EtsAl dissolved in the chiral nematic LC solvent. The polyacetylene film consisted of clockwise or counterclockwise helical structure of fibrils in SEM. Cotton effect was observed in the region of ir — ir transition of the polyacetylene chain in CD spectrum. The high-electrical conductivities of 1.5 1.8 x... 

In 2005, Wang and coworkers reported a new bifunctional binaphthyl-derived amine thiourea 16 as an efficient organocatalyst for the Morita-Baylis-Hillman reaction of cyclohexenone with aliphatic, aromatic and sterically hindered aldehydes. The design of the catalyst follows Takemoto s design of a bifunctional motif. This catalytic protocol provided access to useful chiral allylic alcohol building blocks in high yields and high enan-tioselectivities (Scheme 19.21). 

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