α-Amino nitriles tethered to alkenes through a urea linkage undergo intramolecular C-alkenylation on treatment with base by attack of the lithionitrile derivatives on the N'-alkenyl group. A geometry-retentive alkene shift affords stereospecifically the E or Z isomer of the 5-alkenyl-4-iminohydantoin products from the corresponding starting E- or Z-N'-alkenyl urea, each of which may be formed from the same N-allyl precursor by stereodivergent alkene isomerization. The reaction, formally a nucleophilic substitution at an sp 2 carbon atom, allows the direct regioselective incorporation of mono-, di-, tri-, and tetrasubstituted olefins at the α-carbon of amino acid derivatives. The initially formed 5-alkenyl iminohydantoins may be hydrolyzed and oxidatively deprotected to yield hydantoins and unsaturated α-quaternary amino acids., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)