Rhodium , chiral **binap ’ complexes

Enantioselective synthesis of chiral biphenols from dienone (175) is catalysed by a chiral rhodium(I)-BINAP complex, involving a highly selective but traceless tfansfer of central-to-axial chirality. (g)... 

The enantioselective synthesis of axially chiral hydroxy carboxylic acid derivatives 42 was accomplished by the cationic rhodium(I)/BINAP complex-catalyzed [2 + 2 + 2] cycloaddition of a,w-diynes 40 with 2-alkoxynaphthalene-derived alkynyl esters 41 with high yields and ee values (Scheme 9.15) [17],... 

Very recently, Wiedenhoefer272 has devised the first asymmetric 1,6-enyne hydrosilylation/cyclization tandem process using a rhodium(l) catalyst with (R)-276 as chiral ligand where rhodium-BINAP complexes were not effective (Scheme 70). More developments on this reaction are covered in Chapter 11.13. 

Suisse and co-workers have studied the asymmetric cyclization/silylformylation of enynes employing catalytic mixtures of a rhodium(i) carbonyl complex and a chiral, non-racemic phosphine ligand. Unfortunately, only modest enantioselectivities were realized.For example, reaction of diethyl allylpropargylmalonate with dimethylphenyl-silane (1.2 equiv.) catalyzed by a 1 1 mixture of Rh(acac)(GO)2 and (i )-BINAP in toluene at 70 °G for 15 h under GO (20 bar) led to 90% conversion to form a 15 1 mixture of cyclization/silylformylation product 67 and cyclization/ hydrosilylation product 68. Aldehyde 67 was formed with 27% ee (Equation (46)). 

The use of chiral rhodium-BINAP complexes for the asymmetric isomerization of alkenes has been utilized in the industrial synthesis of menthol by Ryoji Noyori (winner of the 2001 Nobel Prize in Chemistry). This synthetic method was industrialized by Takasago International Corporation and provides (—)-menthol to pharmaceutical and food companies worldwide. In this case the catalyst [(S-BINAP)-Rh(COD)] or [(S-BINAP)2-RuC104 ] is used for the asymmetric isomerization of diethylgeranylamine (1.62) to 3-(R)-citronellalenamine (1.63) (Scheme 1.13). 

The discovery of the chiral atropisomeric ligand, BINAP, greatly expanded the number of asymmetric homogeneous hydrogenation catalyses. Rhodium and ruthenium complexes that contain BINAP and similar ligand systems have demonstrated an amazing versatility in the reduction of a wide variety of substrate classes in excellent stereoselectivities and reactivities. (-)-Menthol, a variety of... 

Anilides, bearing a sterically demanding orfho-substituent, are known to exist as atropisomers due to a high rotational barrier around aryl-nitrogen single bond. The cationic rhodium(I)/xyl-BINAP complex-catalyzed enantioselective [2+2+2] cycloaddition of 1,6-diynes with trimethylsilylynamides afforded axiaUy chiral anilides with good to excellent enantioselectivity (Scheme 21.21) [25]. 

Silyl Anion Equivalent. Silylboronic ester 1 reacts as a silyl anion equivalent in the presence of transition metal catalysts. Cyclic and acyclic a,/3-unsaturated carbonyl compounds serve as good acceptors of the silyl groups in conjugate addition of 1 catalyzed by rhodium and copper complexes, giving /3-silylcarbonyl compounds (eq 30). The silylation takes place with high enan-tioselectivity when Rh/(5)-BINAP or Cu/chiral NHC catalysts are used. Three-component coupling of 1, a,/3-unsaturated carbonyl compounds, and aldehydes affords 8-hydroxyketone stereoselec-tively in the presence of a copper catalyst (eq 31). The copper enolate 32 is presumed as an intermediate of the reaction. 

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-... 

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). 

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