Both E- and Z-N′-alkenyl urea derivatives of imidazolidinones may be formed selectively from enantiopure α-amino acids. Generation of their enolate derivatives in the presence of K + and crown-6 induces intramolecular migration of the alkenyl group from N′ to Cα with retention of double bond geometry. DFT calculations indicate a partially concerted substitution mechanism. Hydrolysis of the enantiopure products under acid conditions reveals quaternary α-alkenyl amino acids with stereodivergent control of both absolute configuration and double bond geometry.
- DFT calculations
- quaternary amino acids