Metal-free synthesis of 5-alkylated dihydrobenzimidazo[2,1-a]isoquinolines from pendent unactivated alkenes via double C–H functionalizations

An array of dihydrobenzimidazo[2,1-a]isoquinolines with a wide range of functional groups were achieved with good yields, from a pendent unactivated alkene attached to the benzimidazole core with electronically unbiased sp3 C–H bonds. The reaction involves a peroxide-mediated radical cascade cyclization under metal-, catalyst- and additive-free conditions via double C–H functionalizations. The fused tetrahydropyridines and dihydropyrroles are also applicable in this protocol. Some of the title compounds display good fungicidal and insecticidal activities.