2R:3R-Tartaric acid

Fuganti and co-workers used 2R 3R-tartaric acid for the synthesis of 3-benzamido-2,3,6-trideoxy-L-xy/o-hexose (393). The acid was converted according to a known procedure into 2,3-0-isopropylidene-4-0-p-toluenesulfonyl-L-threitol (388). Reduction of 388 with lithium aluminum hydride gave 4-deoxy- 

Raney Nickel catalyst modified with (2R,3R)-tartaric acid 

Optically active (2R,3R)-dimethoxysuccinimide derivatives 4, prepared from (.R,./ -tartaric acid, arc reduced in excellent yield with high stereoselectivity by sodium borohydride in ethanol at 0- 5 °C to furnish a 20 1 mixture of diastereomeric hydroxylactams 543, which, on treatment with acid, give rise to the formation of the enantiomerically pure chiral /V-acylimini-um ions 6, 

Table 4.4. Effects of inorganic salts, added to the (2R,3R)-tartaric acid modifying solution, on enantioselectivity in the hydrogenation of MAA on MRNi (mainly according to Harada ).

Figure 4 Representation of the staggered conformers of coordinated (2R,3R)-tartaric acid in the complex [Co phen)2-

Electrodes made fi om Pt covered with Ni powder or Ni-black and modified with (2R,3R)-(+)-tartaric acid were more effective In die reduction of ethyl acetoacetate ee values of 8-12% were obtained. 

Nitta et al. also confirmed these effects using Ni-silica catalysts modified with (2R,3R)-tartaric acid in the hydrogenation of methyl acetoacetate (Figure 5.9.) They showed the effects on optical selectivity of the concentration of methyl (R)-(-)-3-hydroxybutyrate, which had been previously added to the reaction mixture. 

Figure 3 Newman projections of the staggered conformers of (A) (ft)-malic acid (X = H) and (2R,3R)-tartaric acid

Illes, R., Kassai, Cs., Pokol, Gy., Fogassy, E., and Kozma, D. Thermoanalytical study of 0,0 -dibenzoyl-(2R.3R)-tartaric acid - Part III. SMC-s formation with chiral secondary alcohols, J. Therm. Anal, and Cal. 2002, 68, 679-685. 

Figure 35, Top Enantiomorphous crystals of sodium ammonium tartrate. Hemihedral facets are marked by an h. Bottom (+)-(2R,3R)-tartaric acid (left) and (-)-(2S,35)-tartaric acid (right).

Nemak, K., Acs M., Jaszay M.Zs., Kozma, D., and Fogassy, E. Study of die diastereoisomers formed between pipecolic acid N-alkylanilides and 2R,3R-tartaric acid or 0,0 -dibenzoyl-2R,3R-tartaric acid. Do the tartaric acids form molecular complexes instead of salts during optical resolutions , Tetrahedron 1996, 52, 1637-1642. 

Let s return for a last look at Pasteur s pioneering work. Pasteur took an optically inactive tartaric acid salt and found that he could crystallize from it two optically active forms having what we would now call the 2R,3R and 2S,3S configurations. But what was the optically inactive form he started with It couldn t have been meso-tartaric acid, because meso-tartaric acid is a different chemical compound and can t interconvert with the two chiral enantiomers without breaking and re-forming chemical bonds. 

Kozma, D., Bocskei, Zs., Kassai, Cs., Simon, K., and Fogassy, E. Optical resolution of racemic alcohols by diastereoisomeric complex formation with 0,0 -dibenzoyl-(2R,3R)-tartaric acid, the crystal structure of the (-)-lR,2 S, 5R-menthol.O,0,-dibenzoyl-(2R,3R)-tartaric acid complex. J. Chem. Soc. Chem. Commun. 1996, 753-754. 

Figure 5.3. Effect of loading of Ru on enantioselectivity in the hydrogenation of ethyl acetoacetate into ethyl 3-hydroxybutyrate over Ru-silica catalysts modified with (2R,3R)-tartaric acid (reduction time 0.5 (upper curve) or 5 h (lower curve) crystallite sizes after 0.5h reduction time were 1.6 nm (at 1.5% Ru), 4.5 nm (at 4.2% Ru) or 8 nm (at 11.5% Ru) (according to Vedenyapin et al. ).

Table 7.1. presents the main characteristics of the process involving the reduction of beta-keio butyrate, i) acted upon by Baker s yeast, ii) using a Raney Ni catalyst modified by (2R,3R)-tartaric acid + NaBr, and iii) in the presence of a chiral Ru complex containing chiral diphosphine BINAP. 

The separation of a racemic mixture into its enantiomeric components is termed resolution The first resolution that of tartaric acid was carried out by Louis Pasteur m 1848 Tartaric acid IS a byproduct of wine making and is almost always found as its dextrorotatory 2R 3R stereoisomer shown here m a perspective drawing and m a Fischer projection 

Asymmetric hydrocyanation of aldehydes.3 This reaction can be effected by reaction of aliphatic or aromatic aldehydes with cyanotrimethylsilane and an optically active reagent (1) derived from (2R,3R)-tartaric acid, and dichlorodiisopro-poxytitanium(IV). The actual chiral reagent may be 2, shown by H NMR to be 

Figure 5.9. Effect of the amoimts of previously added methyl ( )-(-)-3-hydroxybutyrate to methyl acetoacetate before hydrogenation on Ni-silioa catalyst modified with (2R,3i )-tartaric acid ( ) (according to Nitta et al. and the hydrogenation of ethyl acetoacetate on Raney nickel catalyst modified with (2R,3R)-tartaric acid (o) (according to Chernysheva et al

If more than one chiral center is present, the configuration at each is specified by the symbol R or S together with the number of the chiral atom. Thus the configuration of (+)-tartaric acid is known to be that designated in the name (2R,3R)-(+)-tartaric acid  

Sinou and coworkers evaluated a range of enantiopure amino alcohols derived from tartaric acid for the ATH reduction of prochiral ketones. Various (2R,iR)-i-amino- and (alkylamino)-l,4-bis(benzyloxy)butan-2-ol were obtained from readily available (-I-)-diethyl tartrate. These enantiopure amino alcohols have been used with Ru(p-cymene)Cl2 or Ir(l) precursors as ligands in the hydrogen transfer reduction of various aryl alkyl ketones ee-values of up to 80% have been obtained using the ruthenium complex [93]. Using (2R,3R)-3-amino-l,4-bis(benzyloxy)butan-2-ol and (2R,3R)-3-(benzylamino)-l,4-bis(benzyloxy)butan-2-ol with [lr(cod)Cl]2 as precursor, the ATH of acetophenone resulted in a maximum yield of 72%, 30% ee, 3h, 25 °C in PrOH/KOH with the former, and 88% yield, 28% ee, 120 h with the latter. 

The nomenclature of optically active organic molecules has been revised since their absolute configuration has been determinable via X-ray diffraction (Chapter 6). The equivalent terms are (d)-tartaric acid = (-l-)-tartaric acid = (2R,3R)-tartaric acid (/)-tartaric acid = (—)-tartaric acid = (2S,3S)-tartaric acid mesotartaric acid = (2R,3S) tartaric acid = (2S,3R)-tartaric acid. 

Table 4.7. Rate of formation of (R)-(-)-MHB (mmol h g ) and ee values in the enantioselective hydrogenation of methyl acetoacetate on deposited nickel-kieselguhr catalysts, promoted with 1% noble metals and modified with (2R,3R)-tartaric acid (according to summarized data of Orito et al. ).

Instead of the conventionally used modification by pre-immersion of the catalyst in a solution of modifier, Osawa et al. used an in situ modification during the enantioselective hydrogenation of MAA. Fine nickel powder modified with (2R,3R)-tartaric acid was used and sodium salt was added to the reaction media. By this method the optical yield was increased up to an ee of 79%. Improvement of this method consists in modification in situ of finely reduced Ni-powder by addition of (2R,3R)-tartaric acid and NaBr to the reaction media. In this case, an ee of 89% was obtained in the hydrogenation of MAA. The addition of small amounts of NaBr to the reaction media increased both the ee and the reaction rate, while, in contrast, the rate decreased with the addition of NaBr to the modification solution in 

However, upon dissolution, an epimerization of the anions can occur in the presence of acidic counter-ions. This is particularly true for 16a-16d [39]. The nature of the solvent (MeOH, CHCI3) plays a crucial role on the kinetics of epimerization and the position of the resulting equilibrium. For anions made with a 2R, 3R) tartaric backbone, a A configuration is always preferred in MeOH the selectivity, obtained after a slow equilibration, being independent of the nature of the ester alkyl chain (diastereomeric ratio (d.r.) 3 1). However, in chloroform, the A diastereomer is rapidly obtained and the selectivity is best if the ester side chain is sterically demanding (d.r. 2 1 to 9 1 from 16a to 16d) (Scheme 16). 

The Ru-Cu catalysts modified with TA also proved to be not very effective. Skeletal Cu-Ru catalysts (1 1) were prepared by leaching a Cu-Ru-A1 alloy (15 15 70) at 60°C with a 20% aqueous NaOH solution. Modification of the Cu-Ru (1 1) catalyst was carried out in a 4% aqueous solution of (2R,3R)-tartaric acid at pH 4.4. Hydrogenation of EAA was carried out without solvent at 30°C and 140 bar for 5h. For comparison the hydrogenation of EAA using skeletal Ru and Cu catalysts were also examined under the same conditions. Results are summarized in Table 4.14. 

The effectiveness of enantioselective hydrogenations on chiral modified RNi catalysts depends on many factors. It is influenced by variables of modification procedure, pH of solution modifier, structure of modifier, concentration of modifier, temperature of solution, period of action of modified solution, and presence of additional components. In the case of modifier (2R, 3R)-tartaric acid, it proved very important to add NaBr into the modifying solution. The amount of TA adsorbed on the catalyst determined the effectiveness of the resulting MRNi catalyst 

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