Linked BINOL

Richter, S. N. Maggi, S. Colloredo-Mels, S. Palumbo, M. Freccero, M. Binol quinone methides as bisalkylating and DNA cross-linking agents. J. Am. Chem. Soc. 2004, 126, 13973-13979. 

Complexes of other metals such as gallium, indium, lead, and antimony have also been used as Lewis acids. Catalytic enantioselective meso-epoxide ring-opening reactions using a chiral gallium(III) catalyst (Ga-Li-linked-BINOL) have been reported (Scheme 84).348 The chemical yields are much improved by linking two BINOL units. 

Tiible 11. Enantioselective ring opening of various tneso-epoxides with 4-methoxyphenol (105) promoted by Ga-Ii-linked-BINOL complex (116). 

In 2008, Gong and coworkers introduced a new chiral bisphosphoric acid 19 (Fig. 4) that consists of two BINOL phosphates linked by an oxygen atom for a three-component 1,3-dipolar cycloaddition (Scheme 42) [66]. Aldehydes 40 reacted with a-amino esters 105 and maleates 106 in the presence of Brpnsted acid 19 (10 mol%) to afford pyrrolidines 107 as endo-diastereomers in high yields (67-97%) and enantioselectivities (76-99% ee). This protocol tolerated aromatic, a,P-unsaturated, and aliphatic aldehydes. Aminomalonates as well as phenylglycine esters could be employed as dipolarophiles. 

The cross-linked dendritic BINOLate p-71 (20mol%) was also used as a supported catalyst in the asymmetric cyanosilylation of pivalaldehyde in CH2CI2. The catalyst was reused several times after separation from the reaction mixture by filtration. In 20 consecutive reactions, the cyanohydrine product was formed in >90% yield. Initially, an increase in enantioselectivity was observed from 72%... 

Shibasaki and colleagues achieved further efficient catalysis using a zinc complex as a catalyst [5,14], which was prepared from Et2Zn and linked-BINOL... 

Shibasaki made several improvements in the asymmetric Michael addition reaction using the previously developed BINOL-based (R)-ALB, (R)-6, and (R)-LPB, (R)-7 [1]. The former is prepared from (R)-BINOL, diisobutylaluminum hydride, and butyllithium, while the latter is from (R)-BINOL, La(Oz -Pr)3, and potassium f-butoxide. Only 0.1 mol % of (R)-6 and 0.09 mol % of potassium f-butoxide were needed to catalyze the addition of dimethyl malonate to 2-cy-clohexenone on a kilogram scale in >99% ee, when 4-A molecular sieves were added [15,16]. (R)-6 in the presence of sodium f-butoxide catalyzes the asymmetric 1,4-addition of the Horner-Wadsworth-Emmons reagent [17]. (R)-7 catalyzes the addition of nitromethane to chalcone [18]. Feringa prepared another aluminum complex from BINOL and lithium aluminum hydride and used this in the addition of nitroacetate to methyl vinyl ketone [19]. Later, Shibasaki developed a linked lanthanum reagent (R,R)-8 for the same asymmetric addition, in which two BINOLs were connected at the 3-positions with a 2-oxapropylene... 

A Et2Zn-(5, S)-linked-BINOL (21) complex has been found suitable for chemos-elective enolate formation from a hydroxy ketone in the presence of isomerizable aliphatic iV-diphenylphosphinoylimines.103 The reaction proceeded smoothly and /9- alkyl-yS-amino-a-hydroxy ketones were obtained in good yield and high enantioselectivity (up to 99% ee). A titanium complex derived from 3-(3,5-diphenylphenyl)-BINOL (22) has exhibited an enhanced catalytic activity in the asymmetric alkylation of aldehydes, allowing the reduction of the catalyst amount to less than 1 mol% without deterioration in enantioselectivity.104... 

A multinuclear Zn-binaphthoxide complex prepared from Et2Zn and the linked-BINOL 28 has recently been developed as an effective catalyst for the Michael reaction (Scheme 13) [15], The a-hydroxy acetophenone derivative 29 was a suitable substrate, reacting with the Zn complex to afford the configurationally stable Zn enolate. Reaction with a variety of enones proceeded smoothly and... 

For Type II reactions also a variety of useful compounds can be synthesized by changing the combination of the starting materials. In the Michael reaction with cyclic enones, availability of the La-linked-BINOL complex broadened the scope of the Michael acceptor (Scheme 14). It should be noted that less reactive medium-ring-size cyclic enones (7-9membered ring size) underwent conjugate addition highly enantioselectively (up to > 99 % ee) [17]. 

Scheme14. Use of the La-linked-BINOL complex in the Michael reaction with cyclic enones.

Most recently, Shibasaki et al. reported that the Et2Zn-linked-BINOL complex 3 is an excellent catalyst for the direct asymmetric Mannich-type reaction (Fig. 2)... 

Shibasaki and Groger developed lanthanide/alkali binapthoxide-based Lewis acid-Brpnsted base bifunctional catalysts [44]. One such example, the (R,R)-Ln-M-linked BINOL complex. 

Figure 6.21 The proposed mechanism of Michael reaction of enones with malonates catalyzed by (R, i )-Ln-M-linked BINOL complex, a bifunctional asymmetric catalyst developed by Shibasaki.

The highly enantioselective and diastereoselective asymmetric Mannich-type reaction of N-phosphinoylimines (487) with hydroxyketone (488) was catalysed by (S,S) linked BINOL, affording N-phosphinylated aminoalcohols (489). The observed complementary anti-selectivity, in combination with the facile removal of diphenylphosphinoyl group make this reaction synthetically attractive (Figure 92). ... 

La-linked-BINOL complex 23 was introduced as a stable, storable, and reuse-able asymmetric catalyst for the Michael reaction [120]. Optimization of the reaction between dibenzyl malonate and 2-cyclohexene-1-one in DME afforded the Michael adduct in 94% yield and >99% ee. The extraordinary versatility of LnLB catalyts is also documented in the highly efficient Michael addition of thiols to a,y9-unsaturated carbonyl compounds [121] and tandem Michael-aldol reactions [122]. 

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