Catalytic asymmetric arylation

So far, there is only one report describing the use of chiral NHC-metal complexes in catalytic asymmetric arylation of imines. This was achieved by using C -symmetric cationic NHC-Pd diaquo complex 20 (Scheme 7.6) [38]. The arylation of a variety of A-tosylimines with different arylboronic acids was carried out under mild conditions. The presence of electron-withdrawing or electron-donating substituents on both partners did not seem to affect the reaction and the corresponding chiral diarylamines were obtained in good to excellent yields and high enantiomeric excess. 

The catalytic asymmetric arylation (Heck reaction) of 2,3-dihydrofuran to give (/J)-2,3-di-hydro-2-phenylfuran which, upon Jones oxidation, yields (/ )- 2 (for assignment, see p 439)80. 

The chiral phosphine 31 or 32-rhodium complex catalyzed the addition of arystannanes 30 to N-sulfonylimines 29 to give diarylmethylamines 33 with high enantioselectivity (75-96% ee) [21]. The choice of the chiral monoden-tate phosphine ligand is essential for their catalytic asymmetric arylation. With chelating bisphosphine ligands the arylation was very slow. The authors hypoth-... 

Table I. Catalytic Asymmetric Arylation of 2,3-Dihydrofuran with Aryl Triflatesa...

Table III. Catalytic Asymmetric Arylation of 2,3-Dihydrofuran with Phenyl Triflate (la) Promoted by [Pd (fl)-BINAP 2] Catalysta...

Catalytic asymmetric arylation of alkenes.4 This arylation can be effected by a Heck-type arylation of 2,3-dihydrofuran with an aryl triflatc catalyzed by Pd(OAc)2/(R)-BINAP in the presence of 1,8-bis(dimelhylamine)naphthalcnc (proton sponge) as base. This reaction was used to prepare an antagonist (4) of platelet activating factor. 

For a review on catalytic asymmetric aryl additions see Bolm C, Hildebrand JP, Muniz K,... 

Ozawa, F., Kubo, A. and Hayashi, T. (1991) Catalytic asymmetric arylation of 2,3-dihydrofuran with aryl triflates. J. Am. Chem. Soc., 113, 1417-9. 

The catalytic enantioselective formation of C—C bonds is one of the most fundamental processes in modern organic synthesis for the rapid construction of complex molecules. Arylation methods have their special place in this area due to the importance of aromatic groups in numerous pharmaceuticals (Figure 8.1) [1]. Considerable research endeavors have been undertaken during the past few years in order to optimize existing protocols and widen the scope of molecules that can be accessed. Since the publication by Bohn, in 2001, of a review of catalytic asymmetric arylation reactions, many innovative and practical processes have been developed for the straightforward enantioselective, catalytic introduction of aryl groups [2]. 

Table 3 Catalytic asymmetric arylation of various aldehydes...

Scheme 6.3 Proposed mechanism for the catalytic asymmetric arylation of imines catalyzed by a rhodium complex with a phenyltitanium reagent [6],...

Since the publication by Bolm et al. [3], in 2001, of a review on catalytic asymmetric arylation reactions (Scheme 7.1), many innovative and practical processes have been developed in this area. In this chapter, which concerns the arylation of carbonyl groups (aldehydes, ketones, etc.) and the most important advances that have taken place in the last 10 years or so, enantioselective and nonasymmet-ric arylation of carbonyl groups wHl be discussed, taking into account the different transition-metal catalysts applied. 

In an intermolecular Heck reaction, the nucleophilic component and the alkene are on different molecules. Until now, few applications of asymmetric intermolecular Heck reaction have been conducted, mainly because of problems related to the regioselectivity of this transformation. The first example reported by Hayashi and co-workers in 1991 involved the catalytic asymmetric arylation of 2,3-dihydrofuran 46. Aryl triflates afforded 2-aryl-2,3-dihydrofurans with enantioselectivities of up to 93% ee in the presence of the Pd(OAc)2/BINAP catalytic system. In a... 

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