CuI/I₂-Mediated Synthesis of Iodoisoquinoline-Fused Benzimidazoles

Significance

The iodine-mediated, CuI-catalyzed synthesis of iodoisoquinoline-fused benz­imidazoles from 2-ethynylbenzaldehydes and o-benzenediamines is reported. NIS, NBS and NCS were tested as well; NIS afforded lower yields compared to I₂, NBS afforded the product (single case) in 48% yield, and NCS failed to ­perform as a reagent. The control experiment showed that two equivalents of CuI are sufficient for effecting the ­cyclization step (no incorporation of iodine). The substrate scope was quite well studied, yields range from poor to good, and one of the products (R^¹ = H, R^² = Ph, R^³ = H) was used in Sonogashira, Heck, and Suzuki coupling reactions, demonstrating further versatility.