Tetraaryl-3-Azepines: KOBu/DMSO-Catalyzed Assembly from Diaryldiynes and -Benzylaldimines.

Di(het)aryldiynes smoothly react with -benzylaldimines in a [4 + 3] cycloaddition manner under the action of the KOBu/DMSO system (60 °C, 30 min) to afford pharmaceutically relevant tetra(het)arylsubstituted 3-azepines in up to 71% yield. The process involves the addition of azaallyl anions to one of the triple bonds of diynes followed by prototropic isomerization and cyclization of anionic intermediates with participation of the second triple bond. The cascade mechanism is consistent with quantum-chemical analysis (B2PLYP-D3/6-311+G**//B3LYP-D3/6-31+G* + PCM).