Ligands BINOL

It has also been shown by Mikami et al. that a BINOL-titanium(IV) complex in which the 6,6 position of the BINOL ligand is substituted with bromine catalyzes... 

Scheme 2 Synthesis of BINPHAT anion 15 containing a BINOL ligand...

Qian et al. explored LLB-catalyzed reactions using new BINOL ligands (Scheme 5-35). 

Sc(03SCF3)3 in the presence of a BINOL ligand.113 Optimized conditions involved use of 5-20 mol % of the catalyst along with a hindered amine such as cis-1,2,6-trimethylpiperidine. A hexacoordinate TS in which the amine is hydrogen bonded to the BINOL has been proposed. 

Colloredo-Melz, S. Dorr, R. T. Verga, D. Freccero, M. Photogenerated quinone methides as useful intermediates in the synthesis of chiral BINOL ligands. J. Org. Chem. 2006, 71, 3889-3895. 

Figure 5. Catalytic addition of Et2Zn with a fluorous binol ligand...

Chiral tetranuclear Ti(IV) cluster 19, a cubic structure that consists of four Ti atoms and OHs, and six (7 )-BINOL ligands bridging two Ti atoms as ligands, has been shown to be a novel chiral Lewis acid catalyst for the [2 + 3] cycloaddition reaction with nitrones. Chiral Ti(IV) clusters with 7,7 -substituted (7 )-BINOL ligands have been synthesized to give enhanced enantiomeric excesses up to 78% ee (Scheme 12.17). ... 

Liu et al. 43) prepared chiral BINOL ligands bearing dendritic Frechet-type polybenzyl ether wedges ((J )-41-(J )-44), which were assessed in enantioselective Lewis acid-catalyzed addition of Et2Zn to benzaldehyde. 

TABLE 32. Results of the aluminum-catalyzed asymmetric Baeyer-VilUger oxidation using chiral BINOL ligand and achiral and chiral hydroperoxides... 

Incorporation of substituted BINOL ligands improved the enantioselectivity of asymmetric Baeyer-Villiger oxidations of prochiral cyclobutanones with CHP and... 

The catalytic properties of the dendritic BINOL ligand (S)-l (Fig. 6.33) already mentioned in Section 4.2.3.2 (Fig. 4.70) in the catalytic stereoselective reaction of benzaldehyde with diethylzinc were compared with those of unsubstituted... 

Related branched catalysts with BINOL ligand units at the periphery were investigated by Chow and Wan (Fig. 6.35) [53] after model studies had revealed that the catalytic sites should be so far from one another that no intramolecular interaction was to be feared. 

In one of the earliest reports on enantioselective radical reactions, chiral Lewis acid mediated conjugate addition followed by enantioselective H-atom transfer a to a carbonyl was reported by Sato and co-workers (Scheme 3) [22], The single point binding chiral aluminum complex presumably coordinates to the carbonyl oxygen of the lactone as shown in 10. The strong Lewis acidity of the aluminum complex activates the substrate 7 to nucleophilic conjugate addition, which is followed by an enantioselective H-atom transfer from BuaSnH in a chiral environment provided by BINOL ligand in 8. Only 28% ee was observed for product 9. 

New substituted BINOL ligands have been obtained by directed ort/io-lithiation or Suzuki cross-coupling.104 The ligand (R)-(38) has shown improved catalytic properties for the asymmetric diethylzinc addition to aromatic aldehydes. 

A facile and highly selective indium(0)-mediated allylation of hydrazones utilizing BINOL ligands has been described.141 Chiral (7 )-3,3 -bistrifluoromethyl-BINOL has afforded homoallylic amines in up to 97% ee. 

Asymmetric alkylation of benzaldehyde can be performed in a toluene/FC-72 biphasic system with Ti(0-iPr)4 and the fluorous BINOL ligand 7 (Figure 2) with reasonable yield and enantioselectivity [24]. The asymmetric hydrogen-transfer reduction of ketones works fairly... 

As in the case of the catecholate ligands the complexation of dianionic BINOL ligands can be achieved under aqueous conditions (Eq. 14b, Table 11). 

The use of the zinc complex of the BINOL ligand 946 in the hDA reaction between Danishefsky s diene 947 and aldehydes proceeds in excellent yield and enantioselectivity to afford dihydropyran-4-ones 948 (Equation 370, Table 45) <2002OL4349>. An asymmetric diethyl zinc addition can occur in tandem with the cycloaddition reaction between Danishefsky s diene 947 and isophthalaldehyde using a related catalyst 949 (Equation 371) <20030L1091, 2005T9465>. 

Fig. 16 BINOL ligands bearing dendritic poly(aryl ether) wedges...

The effectiveness of various substituted BINOL ligands 12-16 in the Zr(IV)-or Ti(IV)-catalyzed enantioselective addition of allyltributyltin to aldehydes was also investigated by Spada and Umani-Ronchi [21], The number of noteworthy examples of asymmetric allylation of carbonyl compounds utilizing optically active catalysts of late transition metal complexes has increased since 1999. Chiral bis(oxazolinyl)phenyl rhodium(III) complex 17, developed by Mo-toyama and Nishiyama, is an air-stable and water-tolerant asymmetric Lewis acid catalyst [23,24]. Condensation of allylic stannanes with aldehydes under the influence of this catalyst results in formation of nonracemic allylated adducts with up to 80% ee (Scheme 3). In the case of the 2-butenyl addition reac-... 

Two routes were developed to eliminate the BINOLate ligand from the platinum (Figure 7). Reaction of the [( )-BIPHEP]Pt[(Y)-BINOEate] with hydrochloric acid gave [(/ )-BIPHEP]PtCl2. The dichloride [(/ )-BIPHEP]PtCl2 was then subject to two equivalents silver triflate to furnish the Eewis acidic triflate [(/ )-BIPHEP]Pt(OTf)2. Alternatively, [(/ )-BIPHEP]Pt[(Y)-BINOEate] was converted directly to the triflate [(/ )-BIPHEP]Pt(OTf)2 by exposure to triflic acid. 

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