Photoinduced Sequential Trichloromethylation/Cyclization of N-Alkenyl Aldehyde Hydrazones to Access Trichloromethylated Diazaheterocycles.

A visible-light-induced trichloromethylation/cyclization reaction of N-homoallyl aldehyde hydrazones with bromotrichloromethane (BrCCl3) using fac-Ir(ppy)3 as the photocatalyst was developed, providing trichloromethylated tetrahydropyridazines in 38-80% yields. Under similar reaction conditions, the reaction of N-allyl aldehyde hydrazones with BrCCl3 afforded trichloromethylated dihydropyrazoles in 47-72% yields. In addition, trichloromethylated tetrahydrodiazepines were also achieved in 20-63% yield. This protocol features mild conditions and good functional group compatibility to install a trichloromethyl group into N-heterocyclic structures.