Inversion of Diaza[5]Helicenes Through an N−N Bond Breaking Pathway

1,1’,10,10’‐Biphenothiazine and its S,S,S’,S’‐tetroxide are diaza[5]helicenes with N−N linkages. Kinetic experiments on racemization together with DFT calculations revealed that they undergo inversion through the N−N bond breaking pathway rather than the general conformational pathway. In these diaza[5]helicenes with this inversion mechanism, the reduction of electronic repulsion in the N−N bond by modification of S to SO2 at the outer position of the helix led to a significantly higher inversion barrier, 35.3 kcal/mol, compared to [5]helicene. 1,1’,10,10’‐Biphenothiazine S,S,S’,S’‐tetroxide was highly resistant to acid‐mediated N−N bond breaking and racemization under acidic conditions. Diaza[5]helicenes with N−N linkages were found to racemize through the N−N bond‐breaking pathway by kinetic experiments and DFT calculations. Modification of S to SO2 at the outer position of the helix reduced the electronic repulsion in the N−N bond, resulting in a significant increase in the inversion barrier.