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 α-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 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.