Construction of All-Carbon Quaternary Stereocenters by Scandium-Catalyzed Intramolecular C–H Alkylation of Imidazoles with 1,1-Disubstituted Alkenes

The exo-selective C–H cycloaddition of
imidazoles to 1,1-disubstituted alkenes has been achieved for the
first time by using half-sandwich scandium catalysts. A wide range
of imidazole compounds bearing various 1,1-disubstituted aliphatic
alkenes, styrenes, dienes, and enynes have been selectively converted
in high yields to the corresponding bicyclic imidazole derivatives
bearing β-all-carbon-substituted quaternary stereocenters. By
using a chiral half-sandwich scandium catalyst, the asymmetric exo-selective cyclization has also been achieved with a
high level of enantioselectivity.