Acyclic 'N'-Acyliminium Ions in the Synthesis of alpha-Amino Acids

摘要

N-Acyliminium ions have been used in the synthesis of alpha-amino acids mainly inintermolecular reactions with classical nucleophiles. Reactions with modern regioselective nucleophiles, like silicon substituted pi-systems were rare at the beginning of the investigation. Very little was known about the synthesis of alpha-amino acids using intramolecular N-acyliminium reactions. However, acyclic N-acyliminium ions, whereby R(3) or R(4) is a protected carboxylic acid group, are potent glycine cation equivalents, and thus likely suited for the synthesis of a wide variety of alpha-amino acids. The salient difference between the ordinary N-acyliminium ion intermediates studied in the group and the glycine cation is the extra electron-withdrawing carboxyl function on the iminium carbon atom. Investigations towards the use of glycine cation precursors will provide new information on the reactivity of the ionic intermediate as a function of substitution pattern. Investigation in this area of N-acyliminium ion chemistry may contribute to a better understanding of the reactivity of the N-acyliminium ion species, and lead to new efficient routes for the preparation of functionalized natural and unnatural amino acids.