ASYMMETRIC MEMORY AT HETEROATOMS

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Methods for synthesis of optically pure boron complexes, amino acids, amides, and esters are proposed. The critical new feature of the method depends on control of boron stereochemistry in a chiral "ate" complex by crystal lattice effects. The cyclic "ate" complex obtained from the boron reagent and a chiral difunctional substrate is formed as a mixture of diastereomers, but crystallization allows complete conversion into one crystalline isomer. Subsequent chemical transformations would be performed below the temperature for diastereomer interconversion via reversible "ate" complex dissociation, and would take advantage of the "asymmetric memory" of temporarily stereogenic boron. Applications of this concept to the synthesis of natural and unnatural amino acids are described, including methods for catalytic enolate alkylation. A new method for enantiocontrolled enolate protonation is proposed using Lewis acid induced internal proton return. Finally, some of the above methods will be used in short routes to specific chiral atropisomers and unusual chiral boron catalysts.