Stereodynamism in Chiral Polyaromatic Phosphepines

In the present experimental-computational study, we demonstrate that the stereodynamism of phosphahelicenoids can be used to afford diastereoisomers of chirally perturbed polyaromatics fused with a phosphepine ring (seven-membered P-cycle). The phosphahelicenoids have been synthesized through a stereospecific approach from commercially available BINAPs. In particular, using the combination of NMR, X-ray diffraction, and chiral HPLC experimental techniques with DFT and higher level ab initio calculations, we highlight a complex interplay between the inversion at the phosphorus stereocenter and the epimerization of the helicenoid framework, as well as a competition with a rearomatization reaction through P-extrusion. The impact of the conformational modifications on the structure have been studied through X-ray diffraction. The spectroscopic properties, in particular, of chiroptical nature, including circularly polarized luminescence, are also discussed in detail and compared to DFT and ADC(2) models.