Intramolecular Vinylation of Secondary and Tertiary Organolithiums

Deprotonation of benzylic ureas, carbamates, and thiocarbamates
bearing N′-alkenyl substituents generates
carbanions which undergo intramolecular migration of the alkenyl group
to the carbanionic center. Solvolysis of the urea products generates
α-alkenylated amines. With an enantiomerically pure starting
urea, migration proceeds stereospecifically, generating in enantiomerically
enriched form products containing allylic quaternary stereogenic centers
bearing N. Computational and in situ IR studies suggest
that the reaction, formally a nucleophilic substitution at an sp2 carbon atom, proceeds by a concerted addition-elimination
pathway.