The exo-selective C-H cycloaddition of imidazoles to 1,1-disubstitutedalkenes 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 -all-carbon-substituted