Binaphtholate complex

Yokomatsu, T., Yamagishi, T., and Shibuya, S., Enantioselectivity for hydro-phosphonylation of aromatic aldehydes catalyzed by lanthanum binaphthol complex. Remarkable electronic effect of aromatic substituents, Tetrahedron Asymm., 4, 1783, 1993. 

Asymmetric nitroaldol condensation, reaction 9.10, has been used to make an intermediate for the drug S-propanolol 9.61. The condensation reaction is catalyzed by the chiral heterobimetallic binaphthol complex 9.12 with high (>90%) enantioselectivity. 

Better results (80 % ee) have been reported by Mikami, Nakai and co-workers [3c] for the addition of crotyl silane also catalyzed by complex 1. Yamamoto and co-workers [3b] used chiral acyl-oxy boranes to catalyze the Sakurai-Hosomi-reac-tion. While an excellent 96 % ee was obtained for the addition of 2,3 -disubstituted allyl groups, the conversion with parent allyl silane was low (46 %) and the asymmetric induction mediocre (55 % ee). Gauthier and Carreira [5] then made a big leap forward by using the difluorotita-nium-binaphthol complex 3. The catalyst 3 is prepared in situ via the TiF4-binaphthol adduct 4 and formal HF elimination mediated by allyl silane 5. The addition of 5 to aldehydes 6 ( 7) catalyzed by 10 % of 3 proceeds with 61 - 94 % < e and good yields (69-93 %), the best results being observed for aldehydes with tertiary alkyl residues (Scheme 1). 

The chiral-modified binaphthol complex (23) has been prepared (Eq. 10) and shown to be an efficient catalyst for enantioselective Memnich-type reactions [9]. The reaction of imine (24) with ketene silyl acetal in the presence of the catalyst 23 with NMI afforded /3-amino acid derivatives 25 and 26 in high enantioselectivity (Eq. 11). 

Sasai, H., Itoh, N., Suzuki, T., Shibasaki, M. Catalytic asymmetric nitroaldol reaction an efficient synthesis of (S)-propranolol using the lanthanum binaphthol complex. Tetrahedron Lett. 1993, 34, 855-858. 

The asymmetric catalytic cyanosilylation of aldehydes229 and the alkylation of aldehydes with ZnEt2230 using the chiral cyano binaphthol complex Ti(CN)2(i )-BINOL have been developed. 

Rac/meso-isomers of bridged bis(indenyl) zirconium dichlorides can interconvert photochemically.796 This interconversion has been utilized in the stereoselective synthesis of ansa-zirconoccnc binaphtholate stereoisomers.797 Specifically, the rac-meso-mixtures 1034 induced by irradiation in toluene react with 1 equiv. of the dilithium salt of racemic binaphthol to give the racemic binaphtholate complex 1035 (Scheme 253). Analogous reactions with 1 equiv. of the Z (+) enantiomer of dilithium binaphtholate afford the enantiomerically pure [Pg.950]

The binaphtholate complexes (R)-33 were successfully applied in the efficient kinetic resolution of chiral aminoalkenes (Table 5) [101,163,171]. Racemic aminopentenes can be kinetically resolved with resolution factors / as high as 19. The resolution factor value depends dramatically on the nature of the substituent R. Mechanistic studies have revealed that diminished efficiencies in the kinetic resolution of aminoalkenes with aliphatic substituents is caused by an unfavorable state of the Curtin-Hammett pre-equilibrium that favors the mismatching substrate-catalyst complex, whereas in the significantly more efficient kinetic resolutions of aryl-substituted aminoalkenes the matching substrate-catalyst complex predominates the pre-equilibrium [171]. 

The efficient kinetic resolution of chiral aminoalkenes has been achieved utilizing the binaphtholate complexes (R) 38 Ln (Table 11.3) [52, 124]. Various chiral amino pentenes were kinetically resolved with resolution factors/(defined as f= x fefast/fesiow, where is the Curtin Hammett equilibrium constant between the two diastereomeric substrate/catalyst complexes and kfast/fesiow being the ratio between the faster and the slower reaction rate constant) as high as 19 and enantiomeric excess for recovered starting material reaching >80% ee at conversions dose to 50%. The... 

A conceptually different [4-1-2] cycloaddition catalyzed by a chiral lanthanide complex has been disclosed. The inverse electron demand Diels Alder reaction of 3-methoxycarbonyl-2-pyrone (67) and enol ethers or sulfides [135] was catalyzed by a chiral ytterbium(III) triflate-binaphthol complex in the presence of diisopropylethylamine (Scheme 51) [136]. Thermal decarboxylations of bicyclic lactones such as 68 are known to yield dienes which may undergo subsequent pericyclic reactions [137] thus, the adducts of this process are potentially useful chiral building blocks. The nature of the substituent on the 2k component was found to be crucial for the realization of high enantioselectivity. 

Rebiere F, Riant O, Kagan HB (1990) Tetrahedron Asymmetry 1 199 An aluminum-binaphthol complex catalyzes the Diels-Alder reaction of cyclopentadiene and methyl acrylate in 82% yield and 67% ee Maruoka K, Concepcion AB, Yamamoto H (1992) Bull Chem Soc Jpn 65 3501... 

The first catalytic asymmetric radical-mediated allylation was reported in late 1997 by Hoshino and coworkers, who studied the allylation of an a-iodolac-tone substrate, Eq. (19) using trimethylaluminum as Lewis acid and a silylated binaphthol as the chiral catalyst, with triethylborane as radical initiator [62]. Use of one equiv. of diethyl ether was crucial for high enantioselectivity, providing an ee up to 91% in the presence of one equiv. of catalyst, with only a 27% ee in the absence of ether, and poorer ee s when other ethers were employed. In the catalytic version, the ee s dropped off vs. the stoichiometric reaction, with an ee of 81% with 0.5 equiv., and 80% with 0.2 equiv., and 72% with 0.1% catalyst. As in the above example, the presumed chiral intermediate involves complexation of the lactone radical with the Lewis acid-binaphthol complex, with the diethyl ether perhaps as a ligand on the aluminum. 

Asymmetric induction in Diels-Alder cydoadditions has also been observed with binaphthol complexes of lanthanides93-96. 

By virtue of a deep understanding of his LnM3tris(BINOLate)3 complexes (Ln = rare-earth metal, M = alkali metal) based on evidence from X-ray analysis and other experiments, Shibasaki developed chiral heterobimetallic yttrium(in) lithium(i) tris(binaphtholate) complex 22, which can promote the catal) ic enantioselective aza-Michael reaction of metho g lamine to enones in excellent yields with up to 97% ee as a Lewis-acid-Lewis-acid cooperative catalyst (Scheme 2.17). Transformation of the 1,4-adducts 23 afforded the corresponding optically active aziridines 24 in high yields. 

In this procedure, the complex is formed in toluene and can be used over a range of temperatures (0 to -25°C), without any effect upon the enantioselectivity. The originality of this procedure is the amount of water utilized, more than 1 unusual feature of water per sulfide being essential to produce an effective catalyst, both for high enantioselectivity and to retain the catalytic activity of the titanium-binaphthol complex for an extended time. 

The second most important synthetic application of silyl nitronates in C-C bond-forming reactions is their fluoride-mediated addition to aldehydes. Silyl nitronates from secondary nitroalkanes lead to free nitro aldols such as (4), while those from primary nitro alkanes give silylated products. In contrast to the classical Henry reaction, the silyl variant is highly diastereose-lective with aldehydes, furnishing e yfAro-0-silylated nitro aldols (e.g. 5). It is important that the reaction temperature does not rise above 0 °C, otherwise threo/erythro equilibration takes place. The same erythro-nitio aldol derivatives are available by diastere-oselective protonation of silyloxy nitronates (eq 3) (usually the dr is >20 1), while the nonsilylated fAreo-epimers (R = H, dr = 7 3-20 1) are formed by kinetic protonation of lithioxy lithio nitronates in THF/DMPU (eq 4). Other recent modifications of the nitroaldol addition using titanium nitronates or ClSiRs in situ are less selective. It should also be mentioned that there are recent reports about the enantioselective addition of nitromethane to aldehydes in the presence of rare earth binaphthol complexes. 

Hydrogenation catalyzed by palladium, platinum, or Raney nickel of 6 retains the stereogenic center of vicinal carbon, thus provides a complimentary access to chiral vicinal amino alcohols to the conventional routes such as asymmetric epoxide ring opening with amines and their related precursors. Employing lanthanum-(/ )-binaphthol complex to promote asymmetric nitroaldo reaction, followed by the reduction of nitro group, to form amino alcohols serves as the perfect example of this synthetic strategy. ... 

Apart from the aluminum-containing catalyst, the same group also reported a gallium-sodium-binaphthol complex ((/J)-GaSB) and applied them in the Michael reaction of dibenzyl malonate with cyclohexenone (Table 9.3). In the presence of (/ )-GaSB, up to 98% ee was obtained, whereas the yield dropped to 45% even after a prolonged reaction time. Interestingly, when sodium malonate was added to the reaction system as the additive, 2-cyclohexen-l-one could be transformed completely into 1,4-adduct with 96% ee. 

Niobium and tantalum The intermolecular hydroaminoalkylation of unactivated alkenes RCH=CH2 and styrenes with secondary amines ArNHMe to produce amines (229) has been reported to be catalysed by the tantalum and niobium binaphtholate complexes with <98% ee. The reaction has been found to be first order in the amine... 

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