Asymmetric and Geometry-Selective α-Alkenylation of α-Amino Acids

Both E- and Z-N '-alkenyl urea derivatives of imidazolidinones may be formed selectively from enantiopure alpha-amino acids. Generation of their enolate derivatives in the presence of K+ and [18]crown-6 induces intramolecular migration of the alkenyl group from N ' to C alpha with retention of double bond geometry. DFT calculations indicate a partially concerted substitution mechanism. Hydrolysis of the enantiopure products under acid conditions reveals quaternary alpha-alkenyl amino acids with stereodivergent control of both absolute configuration and double bond geometry.