Enantioselective additions of diethylzinc to aldehydes catalyzed by titanate(IV) complex with chiral bidentate bis-amide ligands based on cyclopropane backbone

A set of chiral bis-amide ligands (4a–d and 5a–d) were obtained easily from readily available starting materials in a straightforward manner via acid chloride reaction of the parent Feist’s acid. These ligands have been tested as chiral catalysts for the enantioselective addition of diethylzinc to aromatic aldehydes in the presence of Ti(OiPr)4 as a co-additive. Very good enantioselectivity was obtained for 4-bromobenzaldehyde while in the case of 2,4-dichlorobenzaldehyde very low enantioselectivity was observed. The influence of solvent, temperature and the alkyl group substituents has been studied, and in the best case, an enantiomeric excess upto 95% has been achieved by using only 10 mol % of the chiral bis-amides ligand 5b

Synthesis and Characterization of Some New <em>C<sub>2</sub></em> Symmetric Chiral Bisamide Ligands Derived from Chiral Feist’s Acid

The hemilabile chiral <em>C<sub>2</sub></em> symmetrical bidentate substituted amide ligands (1<em>R</em>,2<em>R</em>)-<strong>5<sub>a-d</sub></strong> and (1<em>S</em>,2<em>S</em>)-<strong>6<sub>a-d</sub></strong> were synthesized in quantitative yield from (1<em>R</em>,2<em>R</em>)-(+)-3-methylenecyclo-propane-1,2-dicarboxylic acid (1<em>R</em>,2<em>R</em>)-<strong>3</strong> and (1<em>S</em>,2<em>S</em>)-(-)-3-methylene-cyclopropane-1,2-dicarboxylic acid (1<em>S</em>,2<em>S</em>)-<strong>3</strong>, in two steps, respectively. The chiral Feist’s acids (1<em>R</em>,2<em>R</em>)-<strong>3</strong> and<strong> </strong>(1<em>S</em>,2<em>S</em>)-<strong>3</strong> were obtained in good isomeric purity by resolution of <em>trans</em>-(±)-3-methylene-cyclopropane-1,2-dicarboxylic acid from an 8:2 mixture of <em>tert</em>-butanol and water, using (<em>R</em>)-(+)-<em>α</em>-methylbenzyl amine as a chiral reagent. This process is reproducible on a large scale. All these new synthesized chiral ligands were characterized by <sup>1</sup>H-NMR, <sup>13</sup>C-NMR, IR, and mass spectrometry, as well as elemental analysis and their specific rotations were measured. These new classes of <em>C<sub>2</sub></em> symmetric chiral bisamide ligands could be of special interest in asymmetric transformations