Variations of bistricyclic aromatic enes: Mono-bridged tetraarylethene naphthologs

The syntheses, molecular and crystal structures, NMR spectroscopic study, and DFT computational study of naphthologs of mono-bridged (X = -, O, S, Se, and Te) tetraarylethene (BAE-1s) 11-25 with α,α-, β,β-, and α,β-dinaphthalenyl substituents have been reported. The BAE-1s have been prepared by Barton-Kellog twofold extrusion from the respective chalcogenothiones and diazomethylenebisnaphthylenes. Complete assignments of ¹H- and ¹³C-NMR spectra of 11-25 have been made through 2-dimensional correlation spectroscopy (DQF-COSY, HSQC, HMBC, and NOESY). The corresponding intermediates, thiiranes 33-47, have been also isolated (except 38), and their molecular and crystal structures have been determined. The molecular structures of BAE-1s 12-15, 20, and 22-25 adopted folded-twisted conformations with considerably folded (φ = 30°-57°) tricyclic moieties. The α,α- and α,β-dinaphthalenyl derivatives are more overcrowded than β,β-dinaphthalenyl derivatives. The relief of the steric strain due to the overcrowding around C⁹ = C^9' caused by the presence of naphthalenyl substituents was achieved by their twisting around the single bonds that connect the α-naphthalenyl and β-naphthalenyl moieties to C^9'. The ¹H-NMR spectra have shown shielding of H², H⁷ of 11-25 and the pronounced deshielding of H^8', H^8′ of α,α-dinaphthalenyl-substituted BAE-1s 13-15 in contrast to β,β-dinaphthalenyl-substituted BAE-1s 16-20. The upfield shifts of H², H⁷ suggested conformations in which these hydrogens are located above the planes of the opposing naphthalene rings. DFT calculations of 11-20 have been performed at B3LYP/6-31G(d) and B3LYP/SDD. The results have shown that the global minima of BAE-1s without a chalcogen bridge 11 and 16 are twisted (-sc,-sc)-C ₂-t conformations. The global minima of BAE-1s with a chalcogen bridge are folded-twisted (-sc,-ac)-C ₁-ft conformations for α,α-dinaphthalenyl-substituted BAE-1s 12-15 and either anti- or syn-(-sc,ac)-C ₁-ft conformations for β,β-dinaphthalenyl-substituted BAE-1s 17-20. The pronounced differences between the α,α-dinaphthalenyl and the β,β-dinaphthalenyl derivatives are noted. Dispersion-corrected B3LYP calculations stabilize significantly the α,α-dinaphthalenyl derivatives versus the β,β-dinaphthalenyl derivatives. The geometrical parameters of BAEs-1 11-15 and 20, derived from their molecular X-ray structures and from their B3LYP-optimized geometries are in a good agreement.