Out-of-plane deformation of the azulene ring in crystal structures of simply substituted azulene derivatives

Tetrahedron Letters

Volumn 47, Issue 16, 2006, Pages 2815-2819

  Ohta, Akira ^a   Thanh, Nguyen Chung ^b   Terasawa, Kouhei ^a   Fujimori, Kunihide ^a   Kuroda, Shigeyasu ^b   Oda, Mitsunori ^a  

^a SHINSHU UNIVERSITY   (Japan)

^b UNIVERSITY OF TOYAMA   (Japan)

Author keywords

Azulenes; Density functional calculations; Out of plane deformation; Planarity; Rotational conformers; X ray crystallographic analysis

Indexed keywords

1,3 BIS(4 BROMOPHENYL); 1,3 DI(2 THIENYL)AZULENE DERIVATIVE; AZULENE DERIVATIVE; BENZENE DERIVATIVE; HYDROGEN; UNCLASSIFIED DRUG;

ARTICLE; CRYSTAL STRUCTURE; X RAY ANALYSIS;

EID: 33644997649     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tetlet.2006.02.079     Document Type: Article

References (36)

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25. -1, 2007 independent reflections, 182 parameters, R = 0.061 (I > 2σ(I), 1405 reflections), wR = 0.137, S = 0.807, T = 298 K. Estimated standard deviations for the bond lengths and angles are 0.004-0.007 Å and 0.2-0.4°, respectively, for the non-hydrogen atoms. Crystallographic data excluding structures have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 288903 for 5 and CCDC 289169 for 6, respectively. A copy of the data can be obtained free of charge from CCDC, 12 Union road, Cambridge CB2 1EZ. UK [Direct line: +44 1223 762910, fax: +44 (0) 1223-336033 or e-mail: linstead@ccdc.cam.ac.uk ; deposit@ccdc.cam.ac.uk ].
26. Although Lai et al. have recently reported X-ray crystallographic analysis of 5, we had analyzed its crystal structure independently. Both results are almost the same. However, they did not claim any deformation of the azulene ring, which we have reported herein. F. Wang, M.-Y. Han, K.Y. Mya, Y. Wang, and Y.-H. Lai J. Am. Chem. Soc. 127 2005 10350 10355
27. These values were obtained as a dihedral angle between the mean planes of the azulene five-membered ring and the mean substituted aryl plane; 34.94° and 36.95° for 5 and 35.01° and 41.61° for 6. Average torsion angles are 36.6° for 5 (C2-C1-C1′-C2′ and C2-C3-C1″-C2″) and 37.0° (C2-C1-C2′-S1′ and C2-C3-C2″-S1″) for 6.
28. The twist angles were obtained by the way reported in the following reference: N. Symth, D. Van Eugen, and R.A. Pascal Jr. J. Org. Chem. 55 1990 1937 1940
29. Unusual bond length and angle were not observed in crystal structures of 5 and 6. No short contact between the intermolecular atoms was found for 5 but there is one between one of the sulfur atoms and the hydrogen at 3′ on the thienyl ring of another molecule with a distance of 2.997 Å in 6, assumed to be CH-S interaction. There is no disorder derived from crystal packing. Therefore, these deformations can only be ascribed to the intramolecular steric hindrance.
30. DFT calculations were conducted by using the Mulliken (ver. 2.0.0, IBM Inc.) program.
31. Relative total energies (kcal/mol) of the calculated conformers are as follows: For 6, A : 0, B : 1.005, C : 1.188, D : 0.104, for 7, A : 0, B : 1.417, C : 1.757, D : 0.546, and for 8, A : 0, C : 0.197.
32. The crystal structure of 5 shows slightly shorter atomic distance by 0.026 Å between the C8- and 8a-positions at the azulene ring than that in the calculated structure of 8A. This may cause to a little greater difference of the twisted angles between the crystal structure of 5 and the calculated structure of 8A. Other slightly shorter atomic distances are observed between the C1- and 2-positions at the azulene ring by 0.032 Å and between the C1″ and C2″ carbons at the phenyl group by 0.024 Å than that in the calculated structure of 8A. The other differences are less than 0.015 Å.
33. The rotational barriers of 1-phenyl- and 1-(2-thienyl)azulenes are estimated as 5.33 and 2.67 kcal/mol, respectively, from total energies of the optimized structures with the locked dihedral angles. Calculations were carried out at the B3LYP/6-31G(d) level of theory.
34. 2 at low temperature of -90°C did not show any intrinsic signal broadening based on the rotational process.
35. Quite recently Yamamura et al. reported a non-planar azulene structure in helical molecules: K. Yamamura, S. Kawabata, T. Kimura, K. Eda, and M. Hashimoto J. Org. Chem. 70 2005 8902 8906
36. For other example of a non-planar azulene structure in helicene, see: S. Ito, A. Nomura, N. Morita, C. Kabuto, H. Kobayashi, S. Maejima, K. Fujmori, and M. Yasunami J. Org. Chem. 67 2002 7295 7302