Cross-coupling reactions asymmetric

One of the newer and more fmitful developments in this area is asymmetric hydroboration giving chiral organoboranes, which can be transformed into chiral carbon compounds of high optical purity. Other new directions focus on catalytic hydroboration, asymmetric aHylboration, cross-coupling reactions, and appHcations in biomedical research. This article gives an account of the most important aspects of the hydroboration reaction and transformations of its products. For more detail, monographs and reviews are available (1—13). 

In a very recent work, the Pd-catalysed cross-coupling reactions with arenediazonium salts under aerobic conditions in the presence of a chiral monothiourea ligand were reported (Scheme 25) [106]. Even if this Hgand bears four chiral centres, no test in asymmetric Heck-type reaction has been described so far. 

Optically active amine-thioether ligands (492) have been investigated in nickel-catalyzed asymmetric cross-coupling reactions of Grigard reagents.1338... 

The catalytic asymmetric synthesis of allenes was first achieved by Elsevier and co-workers in 1989 [104]. A palladium-catalyzed cross-coupling reaction of an allenyl-metal compound 250 (M = ZnCl, MgCl or Cu) with iodobenzene in the presence of DIOP 251 gave 252 in 25% ee (Scheme 4.65). The synthesis of 252 by the reaction of 250 (M = Br) with phenylzinc chloride in the presence of a chiral palladium catalyst gave a quantitative conversion but very low enantiomeric excesses (3-9% ee). 

Carbon-carbon bond-forming reactions are one of the most basic, but important, transformations in organic chemistry. In addition to conventional organic reactions, the use of transition metal-catalyzed reactions to construct new carbon-carbon bonds has also been a topic of great interest. Such transformations to create chiral molecules enantioselectively is therefore very valuable. While various carbon-carbon bond-forming asymmetric catalyses have been described in the literature, this chapter focuses mainly on the asymmetric 1,4-addition reactions under copper or rhodium catalysis and on the asymmetric cross-coupling reactions catalyzed by nickel or palladium complexes. 

In the late 1970s and early 1980s, Kumada described nickel-catalyzed asymmetric cross-coupling reactions of 1-arylethylmagnesium chlorides with vinyl bromide in... 

Asymmetric Cross-Coupling Reactions. An attractive method to attach the side... 

The set of strategies leading to symmetrically and asymmetrically functionalized TTF-derivatives is discussed next (see Fig. 2.5). Strategies S2 and S3 are known as cross-coupling reactions and S4 and S5 are termed condensation reactions. S2 and... 

We have developed asymmetric syntheses of isocarbacyclin [3] (Scheme 1.3.2) and cicaprost [4] (Scheme 1.3.3) featuring a Cu-mediated allylic alkylation of an allyl sulfoximine [5-7] and a Ni-catalyzed cross-coupling reaction of a vinyl sulf-oximine [8-10], respectively, transformations that were both developed in our laboratories. The facile synthesis of an allyl sulfoximine by the addition-elimination-isomerization route aroused interest in the synthesis of sulfonimidoyl-sub-stituted aiiyititanium complexes of types 1 and 2 (Fig. 1.3.2) and their application as chiral heteroatom-substituted allyl transfer reagents [11]. 

P. Dtinkelmann, D. Kolter-Jung, A. Nitsche, A. S. Demir, P. Siegert, B. Lingen, M. Baumann, M. Pohl, M. Muller, Development of a donor-acceptor concept for enzymatic cross-coupling reactions of aldehydes, the first asymmetric cross-benzoin condensation. f Am. Chem. Soc. 2002, 124, 12084-12085. 

Table 8.2 shows the results of the cross-coupling reaction between two differently substituted 2-naphthol derivatives using the CuCl-(5)Phbox catalyst. In conclusion, the first catalytic asymmetric oxidative coupling with a high cross-coupling selectivity was accomplished under mild conditions. 

Table 8.2 Asymmetric oxidative cross-coupling reaction with CuCl-(5)Phbox...

A polystyrene-bound chiral aminophosphine-Ni(II) chloride complex catalyzes the asymmetric cross-coupling reaction of a secondary alkyl Grignard reagent with vinyl bromide in a moderate optical yield (25). 

For recent reviews, see Brase S, de Meijere A (1998) Metal-catalyzed cross coupling reactions. Wiley-VCH, Weinheim Link JT, Overman LE (1998) Metal-catalyzed cross coupling reactions. Wiley-VCH, Weinheim Donde Y, Overman LE (2002) Catalytic asymmetric synthesis, 2nd edn. Wiley-VCH, New York... 

Three types of reaction systems have been designed and applied for the enantioposition-selective asymmetric cross-coupling reactions so far. First example is asymmetric induction of planar chirality on chromium-arene complexes [7,8]. T vo chloro-suhstituents in a tricarhonyl("n6-o-dichlorobenzene)chromium are prochiral with respect to the planar chirality of the 7t-arene-metal moiety, thus an enantioposition-selective substitution at one of the two chloro substituents takes place to give a planar chiral monosubstitution product with a minor amount of the disubstitution product. A similar methodology of monosuhstitution can be applicable to the synthesis of axially chiral biaryl molecules from an achiral ditriflate in which the two tri-fluoromethanesulfonyloxy groups are enantiotopic [9-11]. The last example is intramolecular alkylation of alkenyl triflate with one of the enantiotopic alkylboranes, which leads to a chiral cyclic system [12], The structures of the three representative substrates are illustrated in Figure 8F.1. 

F.3. ASYMMETRIC CROSS-COUPLING REACTIONS ACCORDING TO CHIRAL LIGANDS... 

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