R-BINAP

For the performance of an enantioselective synthesis, it is of advantage when an asymmetric catalyst can be employed instead of a chiral reagent or auxiliary in stoichiometric amounts. The valuable enantiomerically pure substance is then required in small amounts only. For the Fleck reaction, catalytically active asymmetric substances have been developed. An illustrative example is the synthesis of the tricyclic compound 17, which represents a versatile synthetic intermediate for the synthesis of diterpenes. Instead of an aryl halide, a trifluoromethanesul-fonic acid arylester (ArOTf) 16 is used as the starting material. With the use of the / -enantiomer of 2,2 -Z7w-(diphenylphosphino)-l,F-binaphthyl ((R)-BINAP) as catalyst, the Heck reaction becomes regio- and face-selective. The reaction occurs preferentially at the trisubstituted double bond b, leading to the tricyclic product 17 with 95% ee. °... 

A novel chiral dissymmetric chelating Hgand, the non-stabiUzed phosphonium ylide of (R)-BINAP 44, allowed in presence of [Rh(cod)Cl]2 the synthesis of a new type of eight-membered metallacycle, the stable rhodium(I) complex 45, interesting for its potential catalytic properties (Scheme 19) [81]. In contrast to the reactions of stabihzed ylides with cyclooctadienyl palladium or platinum complexes (see Scheme 20), the cyclooctadiene is not attacked by the carbanionic center. Notice that the reactions of ester-stabilized phosphonium ylides of BINAP with rhodium(I) (and also with palladium(II)) complexes lead to the formation of the corresponding chelated compounds but this time with an equilibrium be-... 

Fig. 1. P MAS NMR spectrum of (a)Ru-BrNAP/PTA/y-Al203, and (b)Ru-BINAP crt rlex In order to find the characteristics of the immobilized catalyst, asymmetric hydrogenation of the prochiral C=C bond was performed as a model reaction. Firstly, three different homogeneous Ru-BINAP complexes including [RuCl2((R)-BINAP)], [RuCl((R)-BINAP)(p-cymene)]Cl and [RuCl((R)-BINAP)(Benzene)]Cl were immobilized on the PTA-modified alumina. Reaction test of immobilized catalysts showed that [RuCl2((R)-BINAP)] was the most active and selective so all the experiment were done using this catalyst afterwards.

This facilitates intramolecular hydride transfer resulting in a Ru-hydroxy ester complex (66) which readily releases the chiral product. When an (R)-BINAP-Ru catalyst is used, the R enantiomer is obtained in >99% ee. The chirality of the BINAP ligand accounts for the difference in energy between the possible transition states TS and TS. ... 

An alternative approach to hydroboration has utilized a chiral B-H source with either achiral or chiral rhodium complexes.58 The enantiomerically pure reagent (21) is derived from ephedrine. Notably in the reactions with BINAP, a higher enantiomeric excess is produced from (R)-BINAP (6) compared to the Y-form (Scheme 13). 

Intramolecular hydrosilylation of the fe-alkenyl silane yields the chiral spirosilane with high diastereoselectivity (Scheme 30). With 0.3-0.5 mol.% of catalyst consisting of [Rh(hexadiene)Cl]2 and a range of chelating phosphines P-P (P-P = (R)-BINAP (6), (R,R)-DIOP (5)), a maximum chemical yield of spirosilane of 82% was found with 83% enantiomeric excess. These values were improved considerably by the use of the new ligand... 

Pu and co-workers incorporated atropisomeric binaphthols in polymer matrixes constituted of binaphthyl units, the macromolecular chiral ligands obtained being successfully used in numerous enantioselective metal-catalyzed reactions,97-99 such as asymmetric addition of dialkylzinc reagents to aldehydes.99 Recently, they also synthesized a stereoregular polymeric BINAP ligand by a Suzuki coupling of the (R)-BINAP oxide, followed by a reduction with trichlorosilane (Figure 10).100... 

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