Ligands, BINAP

Scheme 1.15 Test reaction with S / P-heterodonor ligands (BINAPs).

Phenylation has also been achieved with the diphosphine ligands BINAP and tol-BINAP. 

Reagents and conditions i, Pd Ligand, NaO Bu, 110°C, Ligand-BINAP or DPPF ii, Pd /Ligand, NaOtBu, t7-C8H17NH2... 

A highly thermostable palladium-phosphine oxazoline catalytic system, shown in Eq. (11.37), has recently been reported to yield high ee under single-mode micro-wave irradiation [54, 55]. The use of this P,N-ligand catalytic system resulted in even higher ee than the P,P-ligand BINAP [56], The reactions were performed in acetonitrile (b.p. 81-82 °C) and superheating increased the temperatures up to 145 °C, as measured by means of a fluoroptic probe. 

The sense of diastereoselectivity in the dynamic kinetic resolution of 2-substi-tuted / -keto esters depends on the structure of the keto ester. The ruthenium catalyst with atropisomeric diphosphine ligands (binap, MeO-biphep, synphos, etc.) induced syn-products in high diastereomeric and enantiomeric selectivity in the dynamic kinetic resolution of / -keto esters with an a-amido or carbamate moiety (Table 21.21) [119-121, 123, 125-127]. In contrast to the above examples of a-amido-/ -keto esters, the TsOH or HC1 salt of /l-keto esters with an a-amino unit were hydrogenated with excellent cwti-selectivity using ruthenium-atropiso-... 

The hydrogenation of allylic alcohols and a,/>-unsaluraled acids leads to products with a very high synthetic potential, and both transformations were used quite early for industrial applications. In both cases Ru complexes with axially chiral biaryl ligands (binap analogues) are the catalysts of choice. Here, we will dis-... 

Noyori using ruthenium complexes of the ligand BINAP has successfully accomplished asymmetric hydrogenation of molecules of this type. With this system a high enantioselectivity can be achieved (97%) albeit at rather high pressures (135 bar). 

Figure 5.25 Schematic representation of the coordination of the complexes [Rh(NBD)(BDPBzPS03)] (51) and [Rh(NBD) (P-P)](0S02Cp3), where P-P = the optically active phosphine ligands BINAP (52a) and DIOP (52b).

Scheme 1.2 Pd-catalysed amination of aryl halides using the chiral ligand Binap.

Whereas the simple bidentate nitrogen ligands proved to be rather limited, the frequent occurrence of a set of four P-phenyl or alkyl substituents, e. g., in coordinated Binap, MeO-Biphep, Josiphos or Duphos (shown, from left to right in Scheme 1.4), offered many more reporters . In this way, one can develop a more detailed NOE picture of how the complexed substrate interacts with the chiral pocket offered by these auxiliaries. From these NOE studies [97, 98] it can be shown that the atropisomeric bidentate ligands Binap and MeO-Biphep tend to have fairly classical axial and equatorial P-phenyl substituents. 

Arylation has also been observed with the diphosphine ligand BINAP. 

The chiral ligand BINAP was originally prepared from 2,2 -binaphthol and resolved by complexation with an optically active Pd complex [ 10]. A new method starting from 2-naphthol was developed (Scheme 3.2) [11], In this method optical resolution was achieved at the stage of BINAP dioxide (BINAPO) by using inexpensive optically active acids such as camphorsul-fonic acid and dibenzoyltartaric acid. 

A new catalytic system has been found - simply mixing [Rh(COD)Cl]2 and chiral bidentate ligands (BINAP or TunePhos) in situ led to a significant improvement (Scheme 6) [38-41], The non-coordinate solvent 1,2-dichloroethane and the counter-ion SbFroom temperature with the [Rh(BINAP)Cl]2 precatalyst, whereas the in situ [Rh(COD)Cl]2/BINAP system is very efficient and achieved... 

The Shibasaki cychzation of mc.vo-cyclohexa-1,4-dienes in the presence of a chiral palladium complex and silver carbonate in l-methyl-2-pyrrolidinone is probably the first example of an enantioselective Heck reaction (Scheme 10.34).60 The enantiomeric excess could be slightly improved by replacing the chiral phosphine ligand BINAP with the corresponding less coordinating arsine ligand, as well as replacing silver carbonate with silver phosphate.61,62... 

Figure 3.16 The important chiral ligand, BINAP [2,2 -bis(diphenylphosphino)-1, V-binaphthylj, S-enantiomer shown...

Asymmetric cyclization to tricyclic ergolines. The ergoline system of ergot alkaloids can be obtained in fairly high enantioselectivity by cyclization of 2 catalyzed by Pd(0) complexed with a chiral ligand and a base. The ligands BINAP,... 

Ru is more fussy about ligands (BINAP is the one usually if it is an allylic alcohol or an a, J-unsaturated carboxylic... 

The famous ligand BINAP controls an intramolecular Heck reaction to give decalin derivative... 

Rhodium-catalyzed addition of boronic acids to enone moiety 89 led to a rhodium-enolate 90 which can be trapped by addition to the adjacent carbonyl function giving functionalized cyclopentanes or cyclohexanes 91. An important feature of this methodology is that this process allows the creation of three contiguous stereocenters with a high level of stereoselectivity. An asymmetric version of this reaction has also been realized with a chiral ligand (BINAP) giving excellent enantiomeric excesses (77 to 95%) (Scheme 34). 

Related Reagents. Phosphinoxazolines (PHOX ligands), BINAP, chiraphos, bisoxazolines. 

Ruthenium(II) complexes may also be used to oxidize N-Boc hydroxylamine in the presence of tert-butylhydroperoxide (TBHP) to the corresponding nitroso dieno-phile, which is subsequently trapped by cyclohexa-1,3-diene to give the hetero Diels-Alder adduct (Entry 1, Scheme 10.26) [51]. A triphenylphosphine oxide-stabilized ruthenium(IV) oxo-complex was found to be the catalytically active species. Use of a chiral bidentate bis-phosphine-derived ruthenium ligand (BINAP or PROPHOS) result in very low asymmetric induction (8 and 11%) (Entry 2, Scheme 10.26). The low level of asymmetric induction is explained by the reaction conditions (in-situ oxidation) that failed to produce discrete, stable diastereomerically pure mthenium complexes. It is shown that ruthenium(II) salen complexes also catalyze the oxidation of N-Boc-hydroxylamine in the presence of TBHP, to give the N-Boc-nitroso compound which can be efficiently trapped with a range of dienes from cyclohepta-1,3-diene (1 h, r.t., CH2CI2, 71%) to 9,10-dimethylanthracene (96 h, r.t., CH2CI2,... 

The famous ligand BINAP controls an intramolecular Heck reaction to give decalin derivatives with good enantiomeric excess. BINAP is the optically pure phosphine built into the palladium catalyst. The presence of silver ions accelerates the reaction as well as preventing double bond isomerization in the original substrate. This time the chiral ligand selects which double bond is to take part in the reaction. The vinyl palladium species is tethered to the alkene and can reach only the same face. The faces of the alkenes are diastereotopic but the two alkenes are enantiotopic and you must know your right from your left to choose one rather than the other. 

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