BINAP-Rh complex

It is worth noting that an opposite sense of enantioface selection is observed in going from the BINAP-Rh complex to the Ru catalyst. Hydrogenation of methyl (Z)-2-(acetamido)cinnamate with the (7 )-BlNAP-Ru catalyst in CH3OH gives the R (not S) product selectively (Figure pq) p g j-g illustrates the... 

SCHEME 11. Structural characteristics of mono- and bis-BINAP-Rh complexes. 

SCHEME 13. NMR spectra of a mixture of BINAP Rh complex and geranylamine. 

Scheme 21). Scheme 22 illustrates an example of kinetic resolution of a racemic allylic alcohol with a 1,3-hydrogen shift. When racemic 4-hydroxy-2-cyclopentenone is exposed to a cationic (/ )-BINAP-Rh complex in THF, the S enantiomer is consumed five times faster than the R isomer (32). The slow-reacting stereoisomer purified as the crystalline ferf-butyldimethylsilyl ether is an intermediate in prostaglandin synthesis (33). These isomerizations may occur via initial Rh-olefinic bond interaction (34). 

Various prochiral olefins are hydroborated by Rh complexes of BINAP or DIOP in up to 96% optical yield (30h, 31). Oxidation of the products provides a convenient way to produce optically active alcohols. Reaction of styrene and catecholborane in the presence of a BINAP-Rh complex at low temperature forms, after oxidative workup, 1-phenylethyl alcohol in 96% ee (Scheme 11) (31). Double stereodifferentiation occurs in the BINAP-Rh catalyzed reaction of 4-methoxy-styrene and an ephedrine-derived chiral borane (32). 

P-NMR spectra of a 1 5 mixture of the BINAP-Rh+ complex and triethylamine in acetone- ... 

A cationic BINAP-Rh complex catalyzes asymmetric isomerization of some allylic alcohols in THF to give chiral aldehydes in moderate ee... 

Certain unsaturated aldehydes may be converted to cyclic ketones by a related mechanism. The formyl group reacts with Rh(I) complexes to form an acyl-Rh hydride species, which undergoes intramolecular reaction with the olefinic linkage present in the same molecule (117a). Asymmetric induction is observed with a chiral diphosphine ligand (Scheme 53) (117b-d). Enantioselective cyclization of 4-substituted 4-pentanals into 3-substituted cyclopentanones in greater than 99% ee is achieved with a cationic BINAP-Rh complex. 

Allylic andHomoaltylic Alcohols In spite of many examples of diastereoselective hydrogenation of chiral allylic alcohols by using achiral Rh or Ir complexes [134], the enantioselective versions were unsuccessful, With a neutral Cy-BINAP-Rh complex, geraniol or nerol is hydrogenated in benzene to produce citronellol with only 50-60% ee [135]. The use of cationic BINAP-Rh complexes markedly reduces the enantioselectivity. 

Catalytic asymmetric intramolecular hydrosilylation of dialkyl- and diarylsilyl ethers of bis(2-propenyl)methanol (245) catalyzed by (R, R)-DIOP-Rh or (R)-binap-Rh complex, followed by Tamao oxidation, gives (2S, 3R)-2-methyl-4-pentene-l,3-diol (247) with 71-93% ee and excellent syn selectivity (syn/anti = 95/5- > 99/1) (equation 96)249. The enantioselectivity of this reaction depends on the bulkiness of the silyl moiety, i.e. the bulkier the substituent, the higher is the enantiopurity of the product, except for the case of 2-MeCgH4 R = Me, 80% ee (binap-Rh) R = Ph, 83% ee (DIOP-Rh) R = 2-McC.fiI I4, 4% ee (DIOP-Rh) R = 3-MeC6H4, 87% ee (DIOP-Rh) R = 3,5-Me2C6H3, 93% ee (DIOP-Rh). This methodology is successfully applied to the asymmetric synthesis of versatile poly oxygenated synthetic intermediate 249 (equation 97)249. 

Figure 3.28 An (S)-BINAP-Rh complex catalyzes atoms are omitted for clarity). Note that BINAP the asymmetric isomerization step in the ligands contain no asymmetric atoms, but the...

Asymmetric catalysis allows chemicals to be manufactured in their enantiomer-ically pure form and reduces derivatisation and multiple purification steps that would otherwise be required. The 2001 Nobel Prize was awarded for two of the most important asymmetric reactions hydrogenations and oxidations. A variety of ligands suitable for asymmetric reductions are available commercially including BINAP, Figure 3.16. A BINAP Rh complex is used in the commercial production of 1-menthol to enantioselectively hydrogenate an alkene bond (Lancaster, 2002). Ru BINAP complexes can be used in asymmetric reductions of carbonyl groups (Noyori, 2005 Noyori and Hashiguchi, 1997). 

The cationic BINAP-Rh complexes catalyze asymmetric 1,3-hydrogen shifts of certain alkenes. Diethylgeranylamine can be quantitatively isomerized in THF or acetone to citronellal di-ethylenamine in 96-99% ee (eq 17). This process is the key step in the industrial production of (-)-menthol. In the presence of a cationic (R)-BINAP-Rh complex, (5)-4-hydroxy-2-cyclopentenone is isomerized five times faster than the (R) enantiomer, giving a chiral intermediate of prostaglandin synthesis. ... 

Enantioselective cyclization of 4-substituted 4-pentenals to 3-substituted cyclopentanones in >99% ee is achieved with a cationic BINAP-Rh complex (eq 18). ... 

Reaction of styrene and catecholborane in the presence of a BINAP-Rh complex at low temperature forms, after oxidative workup, 1-phenylethyl alcohol in 96% ee (eq 19). ... 

Neutral BINAP-Rh complexes catalyze intramolecular hy-drosilylation of alkenes. Subsequent//yPeroxide oxidation produces the optically active 1,3-diol in up to 97% ee (eq 20). ... 

Chiral y-hydroxy ketones meyo-1,4-Bis(siloxy)-2-alkenes undergo regioselective isomerization on treatment with a BINAP-Rh complex. On exposure to Bu NF the enol ether moiety of the products is hydrolyzed (a TBS group can be retained). 

The PS-PEG resin-supported BINAP ligand was prepared and used successfully for the rhodium-catalyzed asymmehic 1,4-addihon reachon in water [29]. BINAP bearing a carboxyhc group at the 6-posihon was immobihzed by an amide bond on an amphiphihc PS-PEG NH2 resin (Scheme 6.7). The PS-PEG BINAP 59 was heated with Rh(acac)(G2H4)2 to form the PS-PEG-BlNAP-Rh complex. The polymeric BINAP-Rh complex showed high catalyhc achvity and high enanhoselectivity in water for the 1,4-addihon of phenylboronic acid to a,P-unsaturated ketones (Scheme 6.8). 

Scheme 6.8 Asymmetric 1,4-addition in water with PS-PEG-BINAP-Rh complex. 

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