Stereodynamism in Chiral Polyaromatic Phosphepines

TL;DR

This study explores how the dynamic behavior of phosphahelicenoids can create chiral polyaromatic compounds with a seven-membered phosphorus ring.

Contribution

The paper introduces a new stereospecific synthesis and analysis of chiral polyaromatic phosphepines using experimental and computational methods.

Findings

Stereodynamism in phosphahelicenoids leads to diastereoisomers of chirally perturbed polyaromatics.

A complex interplay between phosphorus inversion and helicenoid epimerization was observed.

Rearomatization through P-extrusion competes with stereodynamic processes.

Abstract

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.

Stereodynamism of phosphahelicenoid scaffolds can be used to afford diastereoisomers of polyaromatics fused with a chiral seven‐membered P‐ring. In particular, a complex interplay between the inversion at the P centre and helicenoid epimerization, as well as a competition with a rearomatization reaction, takes place.

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