| Abstract
| - Proline-catalyzed diastereoselective aminomethylation of aldehydes using a chiral iminium ion,generated from a readily prepared precursor, provides α-substituted-β-amino aldehydes with 85:15 to 90:10 dr. The α-substituted-β-amino aldehydes can be reduced to β-substituted-γ-amino alcohols, the majordiastereomer of which can be isolated via crystallization or column chromatography. The amino alcoholsare efficiently transformed to protected β2-amino acids, which are valuable building blocks for β-peptides,natural products, and other interesting molecules. Because conditions for the aminomethylation andsubsequent reactions are mild, β2-amino acid derivatives with protected functional groups in the side chain,such as β2-homoglutamic acid, β2-homotyrosine, and β2-homolysine, can be prepared in this way. Thesynthetic route is short, and purifications are simple; therefore, this method enables the preparation ofprotected β2-amino acids in useful quantities.
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