Rhodium catalyzed asymmetric

In 1968,Horner et al. [22] and Knowles and Sabacky [23] independently demonstrated that low but definite enantiomeric excesses (up to 15% ee) were produced in the rhodium-catalyzed asymmetric hydrogenation of simple alkenes using methylpropylphenylphosphine 7 as chiral ligand (Scheme 1). 

Rhodium complexes with chiral dithiolato and dithiother ligands have been studied in rhodium-catalyzed asymmetric hydroformylation. In all instances, enantioselectivities were low.391-393 Catalysis with compounds containing thiolate ligands has been reviewed.394... 

A broad substrate scope for the rhodium-catalyzed asymmetric 1,4-addition has been observed.98 Both arylboronic acids with either electron-donating or electron-withdrawing aryl substituents and alkenylboronic acids can be introduced into acyclic or cyclic enones with high enantioselectivities (Scheme 30). 

Nitroalkenes are good candidates for the rhodium-catalyzed asymmetric 1,4-addition of organoboronic acids. Hayashi et al. reported that the reaction of 1-nitrocyclohexene with phenylboronic acid in the presence of rhodium/ -BINAP catalyst gave 99% ee of 2-phenyl-1-nitrocyclohexane (Scheme 38).117... 

An unusual carbene-thioether hybrid ligand 174 was synthesized and applied in the rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate by Chung and co-workers however, the selectivity and activity were low (Table 27.7, entry 34) [135]. 

Tillack and co-workers developed a rhodium-catalyzed asymmetric hydrosilylation of butadiyne 258 to afford allenylsilane 260 (Scheme 4.67) [106]. Among more than 30 chiral phosphine ligands investigated, the highest enantioselectivity was observed when the catalyst was prepared from [Rh(COD)Cl]2 (1 mol%) and (S,S)-PPM 259 (2 mol%) to afford the optically active allene 260 with 27% ee. Other metals such as Ir, Pd, Pt or Ni were less effective for example, a nickel catalyst prepared from NiCl2 and (R,R)-DIOP 251 or (S,S)-PPM 259 gave the allene 260 with 7-11% ee. 

Rhodium-Catalyzed Asymmetric Hydroformylation of Vinyl Arenes. .. 41... 

Fig. 2 Ferrocenylethyldiphosphine derivatives 6 providing high ee in rhodium catalyzed asymmetric hydroformylation...

Scheme 3 Model rhodium-catalyzed asymmetric hydroformylation asymmetric of vinyl...

Fig. 6 Rhodium-catalyzed asymmetric hydroformylation of styrene using ligands 3 and 23-26. Enantioselectivities obtained at 100 bars of syngas and 60 °C are shown in brackets...

Following the initial work by Hayashi and Miyaura using (5)-binap, several other chiral ligands were reported to achieve high enantioselectivity in the rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to ot,p-enones (Figure 3.18). A polymer-supported (X)-binap analog 42 was also synthesized and it was successfully utilized in the rhodium-catalyzed asymmetric 1,4-addition reactions in water (Figure 3.19)." The stereoselectivities observed in this system are comparable to those obtained in the unsupported Rh/(5)-binap system. It was also... 

By tethering a,p-enones with another carbonyl-containing moiety, Rrische developed rhodium-catalyzed asymmetric 1,4-addition/aldol cyclization reactions." These reactions proceed with high diastereo- and enantioselectivity, furnishing structurally complex cyclic compounds in a single step [Eqs. (3.11-3.13)]. 

Not only organoboron reagents but also organosilicon reagents are suitable nucleophiles in the rhodium-catalyzed asymmetric 1,4-additions to a,p-enones in... 

A rhodium-catalyzed asymmetric synthesis of chiral titanium enolates by 1,4-addition of aryltitanium reagents to a,p-enones under aprotic conditions has... 

Rhodium-catalyzed asymmetric 1,4-addition reactions have been applied to various other a,p-unsaturated compounds as well. Thus, Rh/(5)-binap can catalyze the asymmetric 1,4-addition of arylboroxines to ot,p-unsaturated phosphonates in high yield and ee (Figure 3.37). The key to the success in achieving high yield is the... 

Fumaric and maleic compounds are also suitable substrates in the rhodium-catalyzed asymmetric 1,4-addition reactions. While phosphorus-based chiral ligands, such as (/f)-binap, provide low enantioselectivity for these substrates (<51% ee), chiral diene ligands 38 and 45 are particularly effective for achieving high ee (Figures 3.39 and 3.40). 

As another way of constructing nitrogen-containing heterocycles enantioselec-tively, the use of 3-aIkoxycarbonyl-3-pyrrolines as substrates has also been described in the rhodium-catalyzed asymmetric 1,4-addition reactions (Figure 3.41). Among the conditions examined, it was found that [Rh(OH)(cod)]2/(5)-binap catalyst is uniquely effective for achieving high yield of the 1,4-adducts. 

Other Related Reactions In addition to simple 1,4-addition reactions described so far, other related rhodium-catalyzed asymmetric carbon-carbon bond-forming processes have also been developed. Lautens reported an asymmetric ring-opening of... 

Senda, T. Ogasawara, M. Hayashi, T. Rhodium-Catalyzed Asymmetric 1,4-Addition of Organoboron Reagents to 5,6-Dihydro-2(lH)-pyridinones. Asymmetric Synthesis of 4-Aryl-2-piperidinones. ]. Org. Chem. 2001, 66, 6852-6856. 

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