Lanthanum-lithium-BINOL

Catalytic Asymmetric Synthesis of Nitroaldols Using a Lanthanum-Lithium-BINOL Complex. 

ASYMMETRIC NITROALDOL REACTION USING LANTHANUM-LITHIUM-BINOL DERIVATIVE COMPLEX AS A CATALYST... 

This volume begins with two procedures in the area of catalytic asymmetric synthesis. The first procedure describes the synthesis of (R)-2-Dl PH ENYLPHOSPHI NO-2 -METHOXY-1,1 -BINAPHTHYL (MOP), a chiral ligand that has proven very useful in palladium-catalyzed hydrosilylation of olefins and palladium-catalyzed reduction of allylic esters by formic acid. The next procedure describes the catalytic asymmetric synthesis of nitroaldols using a chiral LANTHANUM-LITHIUM-BINOL COMPLEX, illustrated by the synthesis of (2S,3S)-2-NITRO-5-PHENYL-1,3-PENTANEDIOL. 

USING A LANTHANUM-LITHIUM-BINOL COMPLEX (2S,3S)-2-NITRO-5-PHENYL-1,3-PENTANEDIOL. 

This idea was realized very successfully by Shibasaki and Sasai in their heterobimetallic chiral catalysts [17], Two representative well-defined catalysts. LSB 9 (Lanthanum/Sodium/BINOL complex) and ALB 10 (Aluminum/Lithium/BINOL complex), are shown in Figure 8D.2, whose structures were confirmed by X-ray crystallography. In these catalysts, the alkali metal (Na, Li, or K)-naphthoxide works as a Br0nsted base and lanthanum or aluminum works as a Lewis acid. 

Graduate School of Pharmaceutical Sciences, The University of Tokyo, Japan Lanthanum(III)-Lithium-BINOL Complex [(/f)-LLB and (5)-LLB]... 

Interestingly, almost the first results in asymmetric hydrophosphonylation with acyclic imines revealed that the lanthanum-potassium-BINOL catalyst LPB was more effective than the analog sodium and lithium complexes LSB and LLB, both of which have been shown to be highly efficient in asymmetric C-C bond formations (see Sect. 3). As a representative example, in the presence of LPB (20 mol%) and 5 equiv of dimethyl phosphite the hydrophosphonylation of im-... 

Shibasaki made several improvements in the asymmetric Michael addition reaction using the previously developed BINOL-based (R)-ALB, (R)-6, and (R)-LPB, (R)-7 [1]. The former is prepared from (R)-BINOL, diisobutylaluminum hydride, and butyllithium, while the latter is from (R)-BINOL, La(Oz -Pr)3, and potassium f-butoxide. Only 0.1 mol % of (R)-6 and 0.09 mol % of potassium f-butoxide were needed to catalyze the addition of dimethyl malonate to 2-cy-clohexenone on a kilogram scale in >99% ee, when 4-A molecular sieves were added [15,16]. (R)-6 in the presence of sodium f-butoxide catalyzes the asymmetric 1,4-addition of the Horner-Wadsworth-Emmons reagent [17]. (R)-7 catalyzes the addition of nitromethane to chalcone [18]. Feringa prepared another aluminum complex from BINOL and lithium aluminum hydride and used this in the addition of nitroacetate to methyl vinyl ketone [19]. Later, Shibasaki developed a linked lanthanum reagent (R,R)-8 for the same asymmetric addition, in which two BINOLs were connected at the 3-positions with a 2-oxapropylene... 

LDI-TOF mass spectral analysis of 49 revealed that the structure was a heterobimetallic complex consisting of one lanthanum, three lithiums, and three BINOL moieties.24 The relevant spectra are shown in Figure 10. LDI-TOF mass... 

A bimetallic catalyst prepared from BINOL and lithium aluminum hydride has been found to result in useful asymmetric induction in the Pudovik reaction [17]. The (f )-ALB catalyst 64 (10 mol %) facilitates the addition of dimethyl phosphite to a variety of electron-rich and electron-poor aryl aldehydes in high yield with induction in the range 71-90 % ee. The nature of the solvent is important in this reaction—the induction for addition to benzaldehyde dropped from 85 % ee to 65 % ee when the solvent was changed from toluene to dichloromethane. Aluminum seems to be a key to the success of this reaction, because reaction with benzaldehyde was not as successful with other bimetallic catalysts. BINOL catalysts with lanthanum and potassium gave only 2 % ee, a catalyst with lanthanum and sodium gave a low 32 % ee, and a catalyst with lanthanum and lithium gave only a 28 % ee [18]. Aliphatic aldehydes were not successfully hydrophosphonylated with dimethyl phosphite by catalyst 64 (Sch. 9). Induction was low (3-24 % ee) for unbranched and branched substrates. a,/3-Unsaturated aldehydes were, however, reported to work nearly as well as aryl aldehydes with four examples in the range 55-89 % ee. The failure of aliphatic aldehydes with this catalyst can be overcome by reduction of the product obtained from reactions with a,)3-unsaturated aldehydes. As illustrated by the reduction of 67 with palladium on carbon, this can be done without epimerization of the a-hydroxy phos-phonate. 

The first chiral aluminum catalyst for effecting asymmetric Michael addition reactions was reported by Shibasaki and coworkers in 1986 [82], The catalyst was prepared by addition of two equivalents of (i )-BINOL to lithium aluminum hydride which gave the heterobimetallic complex 394. The structure of 394 was supported by X-ray structure analysis of its complex with cyclohexenone in which it was found that the carbonyl oxygen of the enone is coordinated to the lithium. This catalyst was found to result in excellent induction in the Michael addition of malonic esters to cyclic enones, as indicated in Sch. 51. It had previously been reported that a heterobimetallic catalyst prepared from (i )-BINOL and sodium and lanthanum was also effective in similar Michael additions [83-85]. Although the LaNaBINOL catalyst was faster, the LiAlBINOL catalyst 394 (ALB) led to higher asymmetric induction. 

For example, an effective procedure for the synthesis of LLB (where LL = lanthanum and lithium) is treatment of LaCls 7H2O with 2.7 mol equiv. BINOL dilithium salt, and NaO-t-Bu (0.3 mol equiv.) in THF at 50 °C for 50 h. Another efficient procedure for the preparation of LLB starts from La(0-/-Pr)3 [54], the exposure of which to 3 mol equiv. BINOL in THF is followed by addition of butyllithium (3 mol equiv.) at 0 C. It is worthy of note that heterobimetallic asymmetric complexes which include LLB are stable in organic solvents such as THF, CH2CI2 and toluene which contain small amounts of water, and are also insensitive to oxygen. These heterobimetallic complexes can, by choice of suitable rare earth and alkali metals, be used to promote a variety of efficient asymmetric reactions, for example nitroaldol, aldol, Michael, nitro-Mannich-type, hydrophosphonylation, hydrophosphination, protonation and Diels-Alder reactions. A catalytic asymmetric nitroaldol reaction, a direct catalytic asymmetric aldol reaction, and a catalytic asymmetric nitro-Mannich-type reaction are discussed in detail below. 

Moreover, the combined use of Nal and lanthanum(iii) lithium(i) tris(biphenoxide) 69 was highly effective for the catalytic enantioselective Corey-Chaykovslqr cyclopropanation of enones or N-acylpyrroles with dimethyloxosulfonium methylide (28) (Scheme 2.40). The use of the chiral biphenyldiol in place of BINOL was important for achieving the high enantioselectivity. 

In 1994, Shibasaki et al. reported on the reaction between malonate and enone catalyzed by a lithium-free lanthanum-1,1 -binaphthyl-2,2 -diol (La-BINOL) complex. ... 

Sasai H, Arai T, ShibasaM M. Catal3ftic as3fmmetric Michael reactions promoted by a lithium-free lanthanum-BINOL complex. J. Am. Chem. Soc. 1994 116(4) 1571-1572. 

---