Approaches toward Atropisomerically Stable and Conformationally Pure Diarylamines
Sagar D. Vaidya, Beeta Heydari, Sean T. Toenjes, Jeffrey L. Gustafson
Abstract
Diarylamines possess two potentially atropisomeric C-N axes; however, there are few examples of atropisomerically stable diarylamines in the literature, as the contiguous axes can allow for low energy racemization pathways via concerted bond rotations. Herein, we describe highly atropisomerically stable diarylamines that possess barriers to racemization of 30-36 kcal/mol, corresponding to half-lives to racemization on the decade to century time scale at room temperature. Investigation of the factors that led to the high stereochemical stability suggests that increased conjugation of the aniline lone pair of electrons into a more electron-deficient aryl ring, coupled with intramolecular hydrogen-bonding, locked the corresponding axis into a defined planar conformation, disfavoring the lower energy racemization pathways.