Chiral imidazolines, formation

Racemization of Amino Acids. The synthesis of (7 )-alanine was achieved starting from (S)-alanine via formation of the imidazoline with (S)-proline. This result can he explained in terms of epimerization and stereoselective protonation with asymmetric induction hy the chiral center originating from (S)-proline. 

Optically active imidazolines are generally obtained from enantiopure 1,2-diamines. For example, chiral ferro-cenylimidazolines are prepared from ferrocenyl carboxylic acid 1241 (Scheme 310). Amide 1242 is activated by 0-alkylation with Et30 BF4, generating iminium ether tetrafluoroborate salt 1243. The formation of the imidazoline ring in 1244 is accomplished by condensation of 1243 with the chiral diamine 1245 at room temperature without the need to isolate the intermediate imidate 1243 <20050L4137>. 

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