Ligands binaphthol

A new type of rigid polymer of 1,1-binaphthols was developed recently [41-43]. The 3,3 -crosslinked polymeric binaphthol ligand 18 in combination with AlMe3 was applied as the catalyst for the 1,3-dipolar cydoaddition (Scheme 6.16) [44]. Very high selectivities were obtained when the aluminum catalyst of 18 (20 mol%) was applied to the 1,3-dipolar cydoaddition reaction between nitrone la and al-kene 8a. The only observable diastereomer resulting from the reactions was exo-9a... 

The synthesis of a series of chiral organophosphine oxide/sulfide-substituted binaphtholate ligands has recently been reported by Marks and Yu and their corresponding lanthanide complexes characterized. These complexes, generated in situ from Ln[N(TMS)2]3, cleanly catalysed enantioselective intramolecular hydroamination/cyclisation of 1-amino-2,2-dimethyl-4-pentene albeit with a low enantioselectivity of 7% ee (Scheme 10.82). 

Uemura and coworkers utilized (R)-binaphthol 85 as chiral ligand in place of DET in association with Ti(IV)/TBHP, which not only mediated the oxidation of sulfides to (R)-configurated sulfoxides, but also promoted the kinetic resolution of sulfoxides (equation 50). In this latter process the two enantiomers of the sulfoxide are oxidized to sulfone by the chiral reagent at different rates, with decrease of the chemical yield, but increase of the ee values. Interestingly, the presence of ortho-nilro groups on the binaphthol ligand lead to the reversal of enantioselectivity with formation of the (5 )-configurated sulfoxide. Non-racemic amino triols and simple 1,2-diols have been successfully used as chiral mediators. 

The 3,3 -cross-linked polymeric binaphthol ligand 238 in combination with A1Mc3 is also a highly selective catalyst for the 1,3-dipolar cycloaddition reaction in Scheme 12.69 (345). The only observable diastereomer resulting from the reactions was exo-233, which was obtained with an enantioselectivity of up to 99% ee using the aluminium catalyst of 238 (20 mol%). One of the advances of using a polymeric catalyst is the easy removal and recovery of the ligand from the... 

Uemura et al. [49] found that (R)-1,1 -binaphthol could replace (7 ,7 )-diethyl tartrate in the water-modified catalyst, giving good results (up to 73% ee) in the oxidation of methyl p-tolyl sulfoxide with f-BuOOH (at -20°C in toluene). The chemical yield was close to 90% with the use of a catalytic amount (10 mol %) of the titanium complex (Ti(0-i-Pr)4/(/ )-binaphthol/H20 = 1 2 20). They studied the effect of added water and found that high enantioselectivity was obtained when using 0.5-3.0 equivalents of water with respect to the sulfide. In the absence of water, enantioselectivity was very low. The beneficial effect of water is clearly established here, but the amount of water needed is much higher than that in the case of the catalyst with diethyl tartrate. They assumed that a mononuclear titanium complex with two binaphthol ligands was involved, in which water affects the structure of the titanium complex and its rate of formation. 

Scheme VII classifies potential spectator ligands according to their ligation mode. Ansa, doubly charged A-type ligands, have been prominent in catalytic investigations up to now and are usually employed in a neutral, heteroleptic form. The additional Ln-R moiety directs the catalytic reactivity in a nonspectator manner Due to its kinetic lability, the Ln-R bond is accessible to ligand exchange reactions, as shown in ansa-cyclopentadienyl-supported catalysts for hydrogenation and polymerization reactions [83]. Biphenol or binaphthol ligands [175], the latter of which was recently successfully applied (e.g. in...

An alternative reaction, the addition of an olefinic C—H bond to C=0, is catalyzed by Lewis acidic titanium aryloxide complexes chiral binaphthol ligands give high optical yields.96... 

Methyl- and phenyl-Ti complexes with different chiral ligands have been tested in reactions with aromatic aldehydes. The enantioselectivity of the addition of chiral Ti reagents having a bidentate l,T-binaphthol ligand system to aromatic aldehydes (equation 55) has been also extensively examined. 

Chiral (helical) Lewis acids for asymmetric Diels-Alder catalysis are prepared from titanium tetraisopropoxide 5 and a chiral binaphthol ligand 4 [13]. The titanium reagent 6 plays an important role as chiral template for the fixation of a,fi-unsaturated aldehydes and thereby for the enantioface recognition of substrates. The asymmetric Diels-Alder reaction, e. g., of cyclopentadiene 7 and acrolein 8, is effected in the presence of catalytic (P)-6 (10 mol%), producing the endo adduct 9 (R =R2=H) in 88% ee (Scheme 1). 

Fluorous chiral binaphthol ligands have been used for enantioselective addition of diethyl zinc to aldehydes in a biphasic system [20] (Scheme 3.5). 

Shibaski and co-workers have focused very strongly on the binaphthol ligand framework, which they have foimd to be extremely powerful in this and related catalytic processes. They have been able to manipulate the Ugand backbone ster-ics and electronics to some degree although the synthetic chemistry involved is not trivial [41]. Moreover, there have been some issues over catalyst performance being linked to the synthetic history of the catalyst itself. It was thought possible therefore that complexes could be prepared which possessed... 

Rare earth metal complexes witii stericaUy demanding tris(aryl)silyl-substituted binaphtholate ligands efficiently catalyze asymmetric hydroamination/cyclization of aminoalkenes and the kinetic resolution of a-substituted aminopentenes. The catalytic activities are comparable to... 

The atropoisomerism of binaphthol ligands has been extensively exploited for the preparation of enantiopiure bidentate ligands. These are usually produced in racemic mixtures and subsequently treated with a resolving agent. Alternative pathways... 

MOFs containing pendant hydroxyl groups can be metalated. For example, Lin and coworkers used dipyridyl-substituted binaphthol ligands as pillars in the preparation of the chiral cadmium MOF [Cd3Cl6(L )3]. TEis product reacted with Ti(OPr )4 with deprotonation of the hydroxyl groups (equation 18) to form a material that catalyzes the addition of diethylzinc to aromatic aldehydes. ... 

In 2000, Pu et al. demonstrated asymmetric hetero-Diels-Alder reaction of enamide 40 and Danishefsky s diene 39 to give compound 41 as a precursor to natural compound fumonisins (Scheme 32) [56]. The most effective ligands for this reaction were 3,3 -disilyl substituted binaphthol ligand 42, and enantioselectivity of 41 reached 78% ee. 

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