Photoinduced Tandem Cyclization of Unsaturated Hydrazones with CF 3 CH 2 I to Access Trifluoroethylated Tetrahydropyridazines and Dihydropyrazoles

A visible-light-mediated trifluoroethylation/cyclization reaction of N-homoallyl aldehyde hydrazones with 1,1,1-trifluoro-2-iodoethane (CF₃CH₂I) was developed for the synthesis of trifluoroethylated tetrahydropyridazines. The reaction was conducted under mild conditions with good functional group compatibility. Moreover, the synthesis of trifluoroethylated dihydropyrazoles was also achieved via the trifluoroethylation/cyclization of N-allyl aldehyde hydrazones with CF₃CH₂I.