2-Cyclohexenone/dibenzyl malonate

Moreover, these rare earth heterobimetallic complexes can be utilized for a variety of efficient catalytic asymmetric reactions as shown in Scheme 7 Next we began with the development of an amphoteric asymmetric catalyst assembled from aluminum and an alkali metal.1171 The new asymmetric catalyst could be prepared efficiently from LiAlH4 and 2 mol equiv of (R)-BINOL, and the structure was unequivocally determined by X-ray crystallographic analysis (Scheme 8). This aluminum-lithium-BINOL complex (ALB) was highly effective in the Michael reaction of cyclohexenone 75 with dibenzyl malonate 77, giving 82 with 99% ee and 88 % yield at room temperature. Although LLB and... 

In 2002, Sasai et al. reported the synthesis of dendritic heterobimetal-lic multi-functional chiral catalysts, containing up to 12 l,l/-bi-2-naphthol (BINOL) units at their terminal positions (Fig. 9) [30]. On treating these functionalized dendrimers with AlMe3 and n-Buli, insoluble metallated Al-Ii-bis(binaphthoxide) generation x (GX-ALB) catalysts were obtained, which showed moderate catalytic activity in the asymmetric Michael reaction of 2-cyclohexenone with dibenzyl malonate (Scheme 4). 

Scheme 4 Asymmetric Michael reaction of 2-cyclohexenone with dibenzyl malonate catalyzed by the metallated dendrimer shown in Fig. 9...

Once in the modern organocatalysis era and with the mechanistic rationale for the iminium activation concept in hand, many different and more efficient methodologies have been developed for this particular reaction. For example, and still focused on the use of secondary amines as catalysts, imidazolidine 53a and proline-tetrazole 2a catalysts have been developed for the conjugate addition of malonates to acyclic enones (Scheme 3.17). For the 53a-catalyzed reaction, this proceeded well in terms of yields and enantioselectivities for a wide range of differently substituted arylideneacetones and for cyclohexenone but yields tend to decrease when more bulky substituents were placed around the carbonyl moiety. Importantly, the enantioselectivity of the reaction was very dependent upon the nature of the malonate reagent, observing that dibenzyl malonate and diethylmalonate furnished the best results. The most... 

Moreover, chiral gallium(iii) sodium(i) bis(binaphtholate) 73 effectively catalysed Michael reactions in the presence of NaOt-Bu (Scheme 2.42). For example, the reaction of cyclohexenone with dibenzyl malonate catalysed by 73 provided the corresponding product in 45% yield with 98% ee, while the combined use of 73 and NaOt-Bu provided the Michael addition product in 87% yield with the same enantioselectivity. 

Apart from the aluminum-containing catalyst, the same group also reported a gallium-sodium-binaphthol complex ((/J)-GaSB) and applied them in the Michael reaction of dibenzyl malonate with cyclohexenone (Table 9.3). In the presence of (/ )-GaSB, up to 98% ee was obtained, whereas the yield dropped to 45% even after a prolonged reaction time. Interestingly, when sodium malonate was added to the reaction system as the additive, 2-cyclohexen-l-one could be transformed completely into 1,4-adduct with 96% ee. 

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