TY - JOUR
T1 - Heteromerous Bistricyclic Aromatic Enes
T2 - Dynamic Stereochemistry of Xanthylidene-Anthrones
AU - Suissa, M. Rachel
AU - Cohen, Shmuel
AU - Pogodin, Sergey
AU - Agranat, Israel
N1 - Publisher Copyright:
© 2015 Wiley Periodicals, Inc.
PY - 2015/12/1
Y1 - 2015/12/1
N2 - 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 1H-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.
AB - 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 1H-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.
KW - DFT calculations
KW - DNMR
KW - E,Z-diastereomerization
KW - X-ray crystallography
UR - http://www.scopus.com/inward/record.url?scp=84946200665&partnerID=8YFLogxK
U2 - 10.1002/chir.22500
DO - 10.1002/chir.22500
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AN - SCOPUS:84946200665
SN - 0899-0042
VL - 27
SP - 919
EP - 928
JO - Chirality
JF - Chirality
IS - 12
ER -