Lanthanoid-alkali metal-BINOL

III. Chiral lanthanoid-alkali metal-BINOL complexes (LnMB)... 

The second part of the chapter deals with several kinds of asymmetric reactions catalyzed by unique heterobimetallic complexes. These reagents are lanthanoid-alkali metal hybrids which form BINOL derivative complexes (LnMB, where Ln = lanthanoid, M = alkali metal, and B = BINOL derivative). These complexes efficiently promote asymmetric aldol-type reactions as well as asymmetric hydrophosphonylations of aldehydes (catalyzed by LnLB, where L = lithium), asymmetric Michael reactions (catalyzed by LnSB, where S = sodium), and asymmetric hydrophosphonylations of imines (catalyzed by LnPB, where P = potassium) to give the corresponding desired products in up to 98% ee. Spectroscopic analysis and computer simulations of these asymmetric reactions have revealed the synergistic cooperation of the two different metals in the complexes. These complexes are believed to function as both Brpnsted bases and as Lewis acids may prove to be applicable to a variety of new asymmetric catalytic reactions.1,2... 

II. Chiral, alkali metal free-lanthanoid-BINOL derivative complexes... 

The first part of this chapter describes recent advances in the use of novel, chiral, alkali metal free-lanthanoid-BINOL derivative complexes for a variety of efficient, catalytic, asymmetric reactions. For example, using a catalytic amount of chiral Ln-BINOL derivative complexes, asymmetric Michael reactions and asymmetric epoxidations of enones proceed in a highly enantioselective manner. 

II. CHIRAL, ALKALI METAL FREE-LANTHANOID-BINOL DERIVATIVE COMPLEXES... 

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 the presence of the sodium-containing heterobimetallic catalyst (R)-LSB (10 mol%), the reaction of enone 52 with TBHP (2 equiv) was found to give the desired epoxide with 83% ee and in 92% yield [56]. Unfortunately LSB as well as other bimetallic catalysts were not useful for many other enones. Interestingly, in marked contrast to LSB an alkali metal free lanthanoid BINOL complex, which was prepared from Ln(0- -Pr)3 and (R)-BINOL or a derivative thereof (1 or 1.25 molar equiv) in the presence of MS 4A (Scheme 17), was found to be applicable to a range of enone substrates. Regarding enones with an aryl-substitu-ent in the a-keto position, the most effective catalytic system was revealed when using a lanthanum-(.R/)-3-hydroxymethyl-BINOL complex La-51 (l-5mol%) and cumene hydroperoxide (CMHP) as oxidant. The asymmetric epoxidation proceeded with excellent enantioselectivities (ees between 85 and 94%) and yields up to 95%. 

Hydrophosphonylation, Nitroaldol Reaction (Kaneka Co., Hokko Chemical Industry). First industrial applications of the heterobimetallic catalysts developed by Shibasaki were realized for the synthesis of several chiral-building blocks. The catalysts are aluminum or lanthanoid cations coordinated to two and three binol ligands, respectively. In addition, one or several alkali metals are coordinated to the binol as well. The asymmetric hydrophosphonylation methodology (85) is now being applied to the preparation of several a-amino phosphonic acids... 

The binol ligand has been used extensively in the synthesis of lanthanoid complexes. These compounds are typically bi-metaUic, containing alkali metal ions (M) exemplified by the formula [M3Ln(binaphthoxide)3]. They can be used as catalysts in a wide variety of important organic transformations. ... 

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