title: Heteromerous Bistricyclic Aromatic Enes: Dynamic Stereochemistry of Xanthylidene-Anthrones.
abstract: The heteromerous bistricyclic aromatic ene (BAE) 2,2'-dimethyl-10-(9H-xanthylidene)-9(10H)-anthrone (DMXA) was synthesized by a condensation of 10,10-dichloro-2-methylxanthene with 2-methylanthrone. X-ray crystallography of (E)-DMXA and xanthylidene-anthrone (XA) indicated that the molecules adopt anti-folded conformations with folding dihedral angles of 44°/44° and 39°/41°, respectively. The crystal structure of anti-folded (E)-DMXA does not indicate any xanthenylium-anthracenolate push-pull effect. E,Z-diastereomerization of DMXA was studied by (1) H-NMR coalescence-temperature measurements at different magnetic field strengths and by kinetic equilibration experiments. Free energy of activation for this process was 81.5 (±1.3) kJ/mol. B3LYP/6-311+G(d,p) calculations showed that anti-folded conformers of XA, (E)-DMXA, bianthrone (AA), and dixanthylene (XX) were global minima. The twisted conformers of XA, AA, and XX were local minima (ΔG298 = 16, 18, and 24 kJ/mol) with a substantial dipolar xanthenylium-anthracenolate dipolar contribution for XA. Chirality 27:919-928, 2015. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Oslo and Akershus University College of Applied Sciences, Faculty of Health Sciences, Institute of Pharmacy and Bioengineering, Oslo, Norway.
authors.forename: M Rachel
authors.initials: MR
authors.lastname: Suissa
authors.affiliation: Organic Chemistry, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Shmuel
authors.initials: S
authors.lastname: Cohen
authors.affiliation: Organic Chemistry, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Sergey
authors.initials: S
authors.lastname: Pogodin
authors.affiliation: Organic Chemistry, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Israel
authors.initials: I
authors.lastname: Agranat
keywords: DFT calculations; DNMR; E,Z-diastereomerization; X-ray crystallography