Synthesis of 2,3-dihydroquinazolinimines and 1,3-diiminoisoindolines catalyzed by rare earth metal alkyl complexes through tandem addition/cyclization of nitriles with amines

Abstract

Mononuclear rare earth metal alkyl complexes with an anilido-imino ligand were synthesized and characterized, and their catalytic ability for the formation of dihydroquinazolines and isoindolines from nitriles and amines was investigated. Reactions of rare earth-metal trialkyl complexes RE(CH₂SiMe₃)₃(THF)₂ with proligand HL (L = (o-(NHDipp)C₆H₄CHN(CH₂)₂NC₄H₈, Dipp = 2,6-ⁱPr₂C₆H₃)) in toluene afforded tridentate anilido-imino rare earth metal dialkyl complexes LRE(CH₂SiMe₃)₂ (RE = Gd (1a), Y (1b), Yb (1c), Lu (1d)) in good yields. Further studies showed that these rare earth metal catalysts could achieve tandem addition/cyclization between ortho imine-functionalized benzonitriles and aromatic amines to afford 2,3-dihydroquinazolinimines for the first time. In addition, the catalysts are well applied to the reaction of substituted phthalonitriles with primary aromatic and aliphatic amines, producing various 1,3-diiminoisoindolines in moderate to excellent yields. During the process of the mechanism study, two anilido yttrium complexes LY(NHPh)₂(THF) (7b) and LY(NHDipp)₂ (8b) were isolated by the reaction of 1b with aniline and 2,6-diisopropylaniline, respectively, as well as their catalytic performance.