Lithium binaphtholate catalyst

Nakajima also developed an enantioselective addition of lithium acet-ylides to ketones in the presence of chiral lithium binaphtholate catalyst 8 (Scheme 2.7). This is the first example of the catalytic enantioselective addition of lithium acelylides to carhonyl compounds without the aid of other metal sources, such as titanium(iv) and zinc(n) species. 

Ishihara developed a highly diastereo- and enantioselective direct Man-nich-type reaction of aldimines with 1,3-dicarbonyl compounds using chiral lithium binaphtholate salts as effective Lewis-acid-Bronsted-base catalysts (Scheme 2.5). ° The stereoselectivity of the Mannich products anti-S and syn-7 ) was reversed when the nucleophile was changed from acyclic 1,3-dicarbonyl compound 4 to cyclic compound 6. The molecular flexibility and acidity of the nucleophiles 4 and 6 would be the major factor in differentiating the two reaction pathways. 

Kobayashi et al. have reported the use of a chiral lanthanide(III) catalyst for the Diels-Alder reaction [51] (Scheme 1.63, Table 1.26). Catalyst 33 was prepared from bi-naphthol, lanthanide triflate, and ds-l,2,6-trimethylpiperidine (Scheme 1.62). When the chiral catalyst prepared from ytterbium triflate (Yb(OTf)3) and the lithium or sodium salt of binaphthol was used, less than 10% ee was obtained, so the amine exerts a great effect on the enantioselectivity. After extensive screening of amines, ds-1,2,6-... 

Both enantiomers of binaphthol have found many uses as chiral reagents and catalysts. Thus, they modify reducing agents (e.g., lithium aluminum hydride) for the reduction of ketones to chiral secondary alcohols (Section D.2.3.3.2.) or react with aluminum, titanium or boron compounds to give chiral Lewis acids for asymmetric Diels-Alder reactions (Section D. 1.6.1.1.1.3.) and ene reactions (Section D.I.6.2.). They have also been used as chiral leaving groups in the rearrangement of allyl ethers (Section D.l.1.2.2.) and for the formation of chiral esters with a-oxo acids (Section D. 1.3.1.4.1, and many other purposes. 

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. 

Shibasaki developed the first catalytic enantioselective hydropho-sphonylation of aldimines with the use of chiral heterobimetallic lantha-num(iii) potassium(i) tris(binaphtholate) 89, which provides optically active a-amino phosphonates with high enantioselectivities (Scheme 2.50). Similar to lithium catalyst 26 and sodium catalyst 67, potassium catalyst 89 acts as an acid-base bifunctional catalyst to activate both nucleophiles and electrophiles. In particular, in this reaction, deprotonation of dimethyl phosphite by more basic potassium catalyst 89 was essential for increasing the reactivity and enantioselectivity, while less basic lithium catalyst 26 and sodium catalyst 67 were not effective. 

Asymmetric hydrosilylation of ketones and ketoimines has been demonstrated in the absence of transition metal catalysts. Using catalytic amounts of chiral-alkoxide Lewis bases such as binaphthol (BINOL), Kagan was able to facilitate the asymmetric reduction of ketones (eq 19). This process is believed to arise from activation of the triethoxysilane by mono-alkoxide addition to give an activated pentavalent intermediate, which can undergo coordination of an aldehyde. This highly ordered hexacoordinate transition state directs reduction in an asymmetric manner, with subsequent catalyst regeneration. Brook was able to facilitate a similar tactic for asymmetric reduction by employing histidine as a bi-dentate Lewis base activator of triethoxysilane. A similar chiral lithium-alkoxide-catalyzed asymmetric reduction of imines was demonstrated by Hosomi with the di-lithio salt of BINOL and trimethoxysilane. ... 

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