Al-Li-BINOL

Arai, T., Bougauchi, M., Sasai, H., and Shibasaki, M., Catalytic asymmetric synthesis of a-hydroxy phosphonates using the Al-Li-BINOL complex, /. Org. Chem., 61, 2926, 1996. 

Yamagishi, T., Yokonatsu, T., Suemune, K., and Shibuya, S., Enantioselective synthesis of a-hydroxyphosphinic acid derivatives through hydrophosphi-nylation of aldehydes catalyzed by Al-Li-BINOL complex, Tetrahedron, 52, 11725, 1996. 

The first catalytic asymmetric tandem Michael-aldol reactions were also achieved by the Al-Li-binol complex (ALB), which was prepared from LiAlH4 and binol. The ALB catalysts gave the Michael adducts in up to 99% ee (Eq. (12.2)) [12J. Mechanistic and calculation studies on ALB revealed that ALB is a heterobimetallic complex which acts as a multifunctional catalyst. 

In a variation on this theme, addition of dialkyl phosphites to nitroalkenes was catalyzed by an Al-Li-Binol species (ALB) [62]. Coordination of the nitro group to aluminum and activation of the phosphite tautomer by Li binding was proposed to lead to selective P-C bond formation (Scheme 38). 

In 1996, Shibasaki s group developed highly efficient bimetallic Al-M- / )-BINOL (M = Li, Na, K, or Ba) catalysts for asymmetric Michael reactions of malonic esters to enones, and excellent results were obtained (84-99% enantiomeric excess) (Table 19.1). Mechanistic studies on Al-Li-(/ )-BINOL ent-18 complex revealed that it worked as a multifunctional heterobimetallic asymmetric catalyst. 

In 1997, Feringa s group reported an enantioselective Michael addition of a-nitroesters to a,p-unsaturated ketones in the presence of a catalytic amount of (/ )-ALB ent-18. X-ray structure analysis in combination with NMR studies of the aluminium catalyst showed that Al-Li-BINOL is a mixture of aluminium complexes in solution (Scheme 19.26). 

High diastereoselectvity was achieved in the hydrophosphonylation reaction of chiral a-amino aldehydes using 20 mol% of the Al/Li/BINOL catalyst (ALB) developed by Shibasaki (Scheme 8.63) [172]. The ratio of syn-/anti-isomers was easily controlled by chirality of the ALB catalyst. 

Another highly useful heterobimetallic catalyst is the aluminum-lithium-BINOL complex (ALB) prepared from LiAlH4 and 2 equiv. of (/ )-BINOL. The ALB catalyst (10 mol %) is also effective in the Michael reaction of enones with various malonates, giving Michael products generally with excellent enantioselectivity (91-99% ee) and in excellent yields [23]. These results ate summarized in Table 8D.3. Although LLB and LSB complement each other in their ability to catalyze asymmetric nitroaldol and Michael reactions, respectively, the Al-M-(/ )-BINOL complexes (M = Li, Na, K, and Ba) are commonly useful for the catalytic asymmetric Michael reaction. 

Shibasaki and co-workers [19] reported a catalytic asymmetric tandem Michael-aldol reaction wherein cylopentenone 50, diethylmalonate, and 3-phenylpropanal react in the presence of Al-Li-(R)-BINOL complex catalyst 57 forming the corre-... 

All the above-mentioned LnSB crystals showed similar mass patterns compared to those of Ln-Li-BINOL complexes, though they contained sodium instead of lithium. The oligomeric structure of the catalysts in the reaction mixture was supported by a slightly positive asymmetric amplification in the asymmetric nitroaldol reaction [9]. In addition, quite recently Shibasaki et al. reported the first X-ray crystallographic structure of a lithium-containing heterobime-tallic catalyst of type LnLB, namely the SmLi3tris(binaphthoxide) complex SmLB [8]. 

Shibasald s concept of a cooperative effect exhibited by two different metals (usually an alkali with a group 3 metal or a lanthanide) in heterobimetallic BINOL-derived complexes was also fruitful in consecutive Michael-aldol additions. Thus, Al-Li-bis[binaphthoxide] complex R,R)-449, readily accessible from lithium aluminum hydride and 2 equiv. of (S)-BINOL, functions as a highly... 

Chiral Al complexes with SALEN ligands (Fig. 8.4) showed 10-54% e.e. depending on the type of substituents and nature of X in the ligand [176]. Mechanistic study revealed dimer-monomer equilibrium of catalyst in solution and discussed the possible influence on the values of enantiomeric excess [177] Small values of enantioselectivity ( 30% e.e.) were observed in the reaction of cinnamaldehyde with dimethylphosphite using La/Li/BINOL as a catalyst [176]. 

Shibasaki et al. have reported excellent La/Li/BINOL (LLB) catalytic system prepared from the LaCl3 x 7H2O and BINOL-dilithium salt in the presence of r-BuONa in THF at 50 °C [183]. Using this catalytic system enantiomeric excess in the reaction of dimethylphosphite and aldehydes was increased to 95% (for p-dimethylaminobenzaldehyde). For the aliphatic aldehydes also a better... 

In 2008, the titanium complex of a novel BINOL-based thiazole thioether ligand was found by Li et al. to be an efficient catalyst in the enantioselective... 

The asymmetric hydrogenation of quinoline continues to be of interest. Li et al. reported the asymmetric hydrogenation of a variety of 2-substituted-quinolines to the corresponding tetrahydroquinolines using an Ir-catalyst with a BINOL-derived diphosphonite ligand... 

The mixed-metal Li(/x-0)Al-based complex CeHgO (THF)2 LiAl[(R)-binol]2 has been a source of great interest recently by virtue of its ability to catalyse [69, 70] the conjugate addition of organolithium species to a, -unsaturated... 

Catalytic Enantioselective Hydrophosphonylation of Aldehydes. LLB catalyzes the hydrophosphonylations of aldehydes with dimethyl phosphite to afford a-hydroxy phosphonates with high optical purity (eq 7). In some cases, the aldehyde needs to be added slowly to the mixture of LLB and phosphite in THF. For some aromatic aldehydes, another catalyst, Li[Al(binol)2] (ALB), gives better results. Imines also react with dimethyl phosphite in a highly enantioselective manner when potassium-based complexes (K3[Ln(binol)3], LnPB) are used as catalysts. ... 

Li, X., Hewgley, J., Mnlrooney, C., et al. (2003). Enantioselective Oxidative Biaryl Conphng Reactions Catalyzed by 1,5-Diazadecalin Metal Complexes efficient Formation of Chiral Fnnc-tionalized BINOL Derivatives, J. Org. Chem., 68, pp. 5500-5511. 

Enantioselective Michael addition catalyzed by chiral aluminum Lewis acid is one of the most important methods to obtain enantiomerically pure compounds. As an early work in this fleld, in 1986, Shibasaki and coworkers reported catalytic enantioselective Michael addition of malonates to cyclic enones catalyzed by Li-Al bimetallic catalyst (72) (ALB) derived by premixing LiAlH4 and 2 equivalent of (R)-BINOL in THF (Scheme 6.86) [106, 107]. The structure of (R)-ALB was confirmed by X-ray crystallographic analysis of ALB-cyclohexenone complex. One notable advantage of ALB catalyst is that it works nicely in the tandem Michael-aldol sequence. 

Important achievement in the field was reported by Shibasaki et al. using heterobimetaUic catalysts. It should be pointed out that complexation of BINOL and La was suggested in the presence of Li or Na and desired stmcture of the catalyst was formed under carefully optimized conditions. 

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