posted on 2018-03-07, 14:17authored byMaciej Krzeszewski, Keisuke Sahara, Yevgen M. Poronik, Takashi Kubo, Daniel T. Gryko
Tetraarylpyrrolo[3,2-b]pyrroles (TAPPs) possessing
[1,1′-biphenyl]-2-yl substituents attached to the pyrrolic
nitrogen atoms undergo selective double dehydrogenative cyclization
accompanied by twofold 1,2-aryl migration under oxidative aromatic
coupling conditions. The structure of the product of the rearrangement
has been unambiguously confirmed by X-ray crystallography, and the
reaction pathway is supported by density functional theory (DFT) calculations.
Six-membered ring formation (requiring rearrangement of aryl substituents
around the core) is energetically preferred over seven-membered ring
closure, and a 1,2-aryl shift occurs via arenium cation intermediate.