Variations of bistricyclic aromatic enes: mono-bridged tetraarylethene naphthologs

Abstract

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.