Tartaric acid amides

These differences stimulated our interest and prompted us to study the effects of solvation on (R,R )-tartaric acid amides. Encouraged by the widespread usage ofAMSOL [42] (vide infra) we decided to use it to calculate Gibbs free energies of hydratation. We performed the calculations with the use of the solvation model SM5.4 [43-46] and hamiltonian PM3 [47] for all structures, optimized at the RHF/6-31G level [20],... 

Solvation effects, as calculated with the use of the AMSOL method, affect the confomational preferences of (i ,i )-tartaric acid amides, so that their lowest-energy structures are different from the G+aa conformers favored in isolated molecules. Hydratation favores the Tact conformation for the primary amides and the G-p+p+ conformation for the tertiary amides of (R,R (-tartaric acid. 

The calculated results are in a very good agreement with the experimental data obtained from X-ray and NMR analyses [22, 29, 39]. This seems to indicate that the relatively simple and computationally economical semiempirical SM5.4 model with PM3 hamiltonian is efficient enough in predicting conformational preferences, even for more difficult cases like (R,R)-tartaric acid amides in water solution. 

The mechanism of retention on chiral phases that is based on multiple hydrogen bonding formation involves the formation of base pairs and triple hydrogen bonds between the solutes and the chiral stationary phase 95 Fundamental work in this area has been done by Hara and Dobashi,96 97 using amino acid amide and tartaric acid amide phases. In addition, N,N -2,6-pyridinediyl bis(alkanamides) chemically bonded to silica gel have been described for the resolution of barbiturates 95... 

McNulty, J. et al. Selective Addition of Grignard Reagents to 2,3-0-Isopropylidene Bis-Weinreb Tartaric Acid Amide. 4.3 2001 [152]... 

Since the reaction mixture becomes very gelatinous upon addition of the tartaric acid amide, a powerful motor and a large stirring blade are necessary. 

Since dimethyl sulfate decomposes rapidly in concentrated alkaline medium, addition of the powdered tartaric acid amide must begin immediately after the dimethyl sulfate is introduced. The amide should be added as fast as possible (ca. 20-30 min) within the limits of the capacity of the reflux condenser and the mechanical stirrer. The amount of dimethyl sulfate can be increased up to 2.5 equivalents and fresh benzyltriethyl-ammonium chloride can be added toward the end of the addition. With less rapid addition and stirring, the yield drops to 45-55%. 

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