BINOL fluorous

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

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... 

Zhao and coworkers performed the enanhoselechve aUylahon of benzaldehyde with allyltributylhn in the presence of 20mol% fluorous BINOL 46 or 47 and Ti(iPrO)4 [58]. The highest enanhoselechvities (up to 90% ee) were obtained using a FBS hexane/FC-72 at 0°C. The two ligands gave similar results and, because of... 

Scheme 3.5 Enantioselective carbon-carbon bond formation in a fluorous biphasic system (top), and synthesis of the fluorous BINOL catalyst 18 (bottom) (Cso = camphorsulfonyl) [20],...

Silyl enol ethers. The re media has operational advantag Reductions. The reducu fluorous BINOL (chiral) densi The use of fluorous tin hydnde dehalogenation. ... 

Takeuchi and collaborators reported the condensation of benzaldehyde with Et2Zn at 0 °C in the presence of the complex prepared in situ by mixing Ti(0-i-Pr)4 and fluorous BINOL 5 [15-17]. When the reaction was performed in a toluene/hexane/... 

Other use of the functionalized chiral BINOL includes the 5,5, 6,6, 7, 7, 8,8 -octahydro derivative developed by Chan and coworkers, the titanium complex of which is more effective than BINOL in the enantioselective addition of triethylaluminum and diethylzinc a 4,4, 6,6 -tetrakis(perfluorooctyl) BINOL ligand developed for easy separation of the product and catalyst using fluorous solvents for the same zinc reaction an aluminum complex of 6,6 -disubstituted-2,2 -biphenyldiols used by Harada and coworkers in the asymmetric Diels-Alder reaction a titanium complex of (5 )-5,5, 6,6, 7,7, 8,8 -octafluoro BINOL employed by Yudin and coworkers in the diethylzinc addition, in the presence of which the reaction of the enantiomeric (/f)-BINOL is promoted . 

Several examples of enanhoselective addihon of organometalhc reagents to aromatic aldehydes catalyzed by Ti-complexes of enanhopure fluorous l,l -bi(2-naphthol) (BINOL) derivahves (Figure 5.3) have been disclosed [54—58]. 

Fluorous BINAP ligands such as 1, prepared from the bromo-BINOL precursor(s), coordinate with RuCl2 to form reusable catalysts that have shown activities in hydrogenation of... 

Chiral 4,4, 6, 6 -tetraperfluorooctyl-BINOL 21 was applied to the titanium-catalyzed addition of EtyZn to aromatic aldehydes. The reaction was carried out in a hexane/perfluoromethyldecalin biphasic system at 45°C for 1 h. At this temperature, the reaction mixture became homogeneous and, after the reaction, the two phases were separated by cooling the homogeneous solution to 0°C. The fluorous phase was used nine times to give constant chemical yields (70-80%) and enantioselectivities (54-58% ee). When a triethylaluminum solution in hexane was used instead of EtyZn solution, the reaction mixture became homogeneous at... 

Another approach to facilitate the recovery of catalytic systems relies on the use of fluorinated analogues of classic chiral ligands. The recycling options offered by the fluorous catalysts have been explored in the field of asymmetric addition of dialkylzinc reagents to aldehydes in presence of titanium tetraisopropoxide. In 2000, the groups of Chan ° and Curran reported independently the synthesis of perfluoroallqrl-substituted BINOL ligands and their evaluation in the titanium-mediated enantioselective addition of diethylzinc to aromatic aldehydes in fluorous biphasic system (Scheme 7.27). 

To facilitate catalyst recovery, polymeric and dendrimeric TADDOL, and BINOL ligands have been used for the titanium-catalyzed diethylzinc addition reaction [49]. Moreover, ionic liquids and fluorous solvents have also been used as the reaction media to facilitate the separation of ligands [50]. The microporous metal-organic frameworks prepared from BINOL derivatives were applicable to heterogeneous diethylzinc addition to aldehydes in the presence of excess amount of Ti(O Pr)4 [51]. 

In parallel with the search for catalytic systems, has emerged an impressive amount of results in the field of enantioselective allylation. The pioneering work of Marshall using a chiral (acyloxy)borane (CAB) system [216] was readily followed by titanium/BINOL catalysts [217], leading to homoallylic alcohols with enantiomeric excess up to 98%. An extension of this work in fluorous phase was also developed with 6,6 -perfluoroalkylated BINOLs [218]. Replacing the titanium by zirconium (IV) salts, led to more reactive catalyst for the allylation of aromatic and aliphatic aldehydes [219]. One of the more active catalyst is the zirconium-BINOL system associated with 4-tert-butylcalix [4]arene, which remains active with only 2% of the chiral inductor [220]. The use of activators, such as iPrSSiMe3, iPrSBEt2,... 

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