Michael reaction catalytic asymmetric

Azoniaspirocycles have been derived from L-tartrate for use as phase-transfer catalysts <2002TL9535>. Catalyst 158 was synthesized in a straightforward manner (Equation 36), then used for catalytic asymmetric Michael reactions an example is shown (Equation 37). 

Table 6. Catalytic asymmetric Michael reactions promoted by the AlMbis(R)-binaphthoxide) complex (AMB).

The mechanistic considerations of a catalytic asymmetric Michael reaction suggest that the reaction of a alkali metal enolate derived from a malon-ate derivative with an enone should lead to an intermediary aluminum enolate. Is it possible that such an A1 enolate could then be trapped by an... 

TABLE 8D.l. Catalytic Asymmetric Michael Reaction with LnSB (10 mol %)... 

TABLE 8D.2. Catalytic Asymmetric Michael Reactions Promoted by LSB in CH2C12... 

Another highly useful heterobimetallic catalyst is the aluminum-lithium-BINOL complex (ALB) prepared from LiAlH4 and 2 equiv. of (/ )-BINOL. The ALB catalyst (10 mol %) is also effective in the Michael reaction of enones with various malonates, giving Michael products generally with excellent enantioselectivity (91-99% ee) and in excellent yields [23]. These results ate summarized in Table 8D.3. Although LLB and LSB complement each other in their ability to catalyze asymmetric nitroaldol and Michael reactions, respectively, the Al-M-(/ )-BINOL complexes (M = Li, Na, K, and Ba) are commonly useful for the catalytic asymmetric Michael reaction. 

Recent advances in the catalytic asymmetric Michael reactions have made it possible to achieve enantioselectivity higher than 90% ee in these processes rather routinely. These reactions have just begu n to be used as key steps in the syntheses of natural products or other useful compounds. In many cases, however, more than 10 mol % of catalysts are necessary to achieve high chemical yield and enantioselectivity at present. In consideration of the limited natural resources on... 

B. HIGHLY PRACTICAL CATALYTIC ASYMMETRIC MICHAEL REACTION... 

Asymmetric catalysis with chiral ligands [82] is commonly considered to be advantageous instead of using chiral auxiliaries. Catalytic asymmetric Michael reactions are known [83], but not with iron as the catalytically active metal. Only two reports on iron catalyzed catalytic asymmetric Michael reaction with dipeptides [84] or diamino thioethers [85] exist, but the enantioselectivities were disappointing (18% ee and 10% ee, respectively). 

C. Catalytic, asymmetric Michael reaction promoted by the La-BINOL complex... 

C. Catalytic, Asymmetric Michael Reaction Promoted by the La-BINOL... 

In both catalytic, asymmetric Michael reactions and nitroaldol reactions, enones and/or aldehydes appear to coordinate to the lanthanoid metal. Why, then, is LSB more effective for catalytic, asymmetric Michael reactions, whereas LLB is more effective for catalytic, asymmetric nitroaldol reactions This disparity might arise from slight differences in bond lengths in the chelated intermediate, as well as slight differences in bite angle for the BINOL moiety caused by varying the alkali metal. 

In both types of catalytic asymmetric Michael reactions, the use of 6,6 -substituted BINOL-derived LSB-type catalysts did not result in significantly improved results. 

Figure 31. Proposed mechanism for the catalytic asymmetric Michael reaction promoted by LSB.

Roush, W. R. The catalytic asymmetric Michael reaction of tin(ll) enethiolates. Chemtracts Org. Chem. 1988,1,439-442. 

For recent reviews on catalytic asymmetric Michael reaction, see (a) Krause, N. and Hoffman-Roder, A. (2001) Synthesis, 171. 

Early studies on the catalytic asymmetric Michael reactions were conducted with readily available amines of natural origin as hsted in Fig. 4. (-)-Quinine (1) and (+)-quinidine (2) are pseudo-enantiomeric concerning the aza[2.2.2]bicyclooc-tane and quinohne moiety, and generally give the antipodes. The same situation holds for (-i-)-cinchonine (3) and (-)-cinchonidine (4) which are demethoxylat-ed derivatives of 1 and 2. 

Direct catalytic asymmetric michael reaction of c<-hydroxyketone promoted by Et2Zn/LINKED-BINOL COMPLEX... 

The catalytic asymmetric Michael reaction is one of the most widely used synthetic methods for the asymmetric carbon-carbon bond formation.[1] Among various... 

Table 11.3 Direct catalytic asymmetric Michael reaction with the first generation Et2Zn/ linked-BINOL = 2/1 system (1).

For recent reviews on the catalytic asymmetric Michael reactions (a) Krause, N. and Hoffmann-Roder, A. Synthesis 2001, 171. (b) Comprehensive Asymmetric Catalysis Jacobsen, E. N., Pfaltz, A. and Yamamoto, H., (Eds.), Springer, Berlin, 1999, Chapter 31. 

Catalytic asymmetric Michael reactions represent one of the most important organic synthetic procedures for stereoselective carbon-carbon bond forming reaction,... 

Catalytic asymmetric Michael reactions are one of the most important synthetic methods for obtaining asymmetric centers by enantioselective construction of carbon-carbon bonds [39,40]. The first lanthanoid complex catalyzed Michael... 

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