Unprecedented detection of enantiomerization π-barriers due to restricted aryl torsion: Case of 1,8-di-arylbiphenylenes

Journal of Organic Chemistry

Volumn 72, Issue 26, 2007, Pages 10045-10050

  Lunazzi, Lodovico ^a   Mancinelli, Michele ^a   Mazzanti, Andrea ^a  

^a UNIVERSITY OF BOLOGNA   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

COMPUTATIONAL METHODS; DISCRETE FOURIER TRANSFORMS; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; NUMERICAL METHODS; SUBSTITUTION REACTIONS;

ARYL TORSION; ARYLBIPHENYLENES; ENANTIOMERIZATION;

ENANTIOMERS;

BIPHENYL DERIVATIVE; POLYCYCLIC AROMATIC HYDROCARBON DERIVATIVE;

ARTICLE; CALCULATION; CHEMICAL ANALYSIS; CONFORMATION; DENSITY FUNCTIONAL THEORY; ENANTIOMER; EXPERIMENTAL STUDY; MATHEMATICAL PHENOMENA; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY;

EID: 37549050571     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo701917v     Document Type: Article

References (40)

1. In partial fulfilment of the requirements for the Ph.D. degree in Chemical Sciences, University of Bologna.
2. (a) Mitchell, R. H.; Yan, J. S. H. Can. J. Chem. 1980, 58, 2584-2587.
3. (b) Lunazzi, L.; Mazzanti, A.; Minzoni, M.; Anderson, J. E. Org. Lett. 2005, 7, 1291-1294.
4. (c) Mazzanti, A.; Lunazzi, L.; Minzoni, M.; Anderson, J. E. J. Org. Chem. 2006, 71, 5474-5481.
5. (a) Clough, R. L.; Roberts, J. D. J. Am. Chem. Soc. 1976, 98, 1018-1020.
6. (b) Cozzi, F.; Cinquini, M.; Annunziata, R.; Siegel, J. S. J. Am. Chem. Soc. 1993, 115, 5330-5331.
7. (c) Cozzi, F.; Ponzini, F.; Annunziata, R.; Cinquini, M.; Siegel, J. S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1019-1020.
8. (d) Zoltewicz, J. A.; Maier, N. M.; Fabian, W. M. F. Tetrahedron 1996, 52, 8703-8706.
9. (e) Zoltewicz, J. A.; Maier, N. M.; Fabian, W. M. F. J. Org. Chem. 1996, 61, 7018-7021.
10. (f) Thirsk, C.; Hawkes, G. E.; Kroemer, R. T.; Liedl, K. R.; Loerting, T.; Nasser, R.; Pritchard, R. G.; Steele, M.; Warren, J. E.; Whiting, A. J. Chem. Soc., Perkin Trans. 2 2002, 1510-1519.
11. (g) Tumambac, G. E.; Wolf, C. J. Org. Chem. 2005, 70, 2930-2938.
12. Lai, Y.-H. J. Chem. Soc., Perkin Trans. 2 1986, 1667-1670.
13. (a) House, H.; Hrabie, J. A.; Van Derveer, D. J. Org. Chem. 1986, 51, 920-929.
14. (b) House, H.; Holt, J. T.; Van Derveer, D. J. Org. Chem. 1993, 58, 7516-7523.
15. (c) Lunazzi, L.; Mancinelli, M.; Mazzanti, A. J. Org. Chem. 2007, 72, 5391-5394.
16. Cross, W.; Hawkes, G. E.; Kroemer, R. T.; Liedl, K. R.; Loerting, T.; Nasser, R.; Pritchard, R. G.; Steele, M.; Watkinson, M.; Whiting, A. J. Chem. Soc., Perkin Trans. 2 2001, 459-467.
17. Lai, Y.-H.; Chen, P. J. Chem. Soc., Perkin Trans. 2 1989, 1665-1670.
18. Anderson, J. E.; Casarini, D.; Lunazzi, L. Tetrahedron Lett. 1988, 29, 3141-3144.
19. 3a
20. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Gammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision D.01; Gaussian Inc.: Pittsburgh, PA, 2004.
21. In a theoretical paper describing compounds analogous to 1, only one of the two possible anti conformers was, inexplicably, considered (see: Bigdeli, M. A.; Moradi, S.; Nemati, F. J. Mol. Struct. THEOCHEM 2007, 807, 125 135).
22. Greater stability of the anti-syn conformer might be due to the so-called CH-π interactions (see: Nishio, M.; Hirota, M; Umezawa, Y. The CH/π Interaction: Evidence. Nature, and Consequences; Wiley: New York, 1998.) that are possible in the anti-in but not in the anti-out. Also, the anti-out might be destabilized by the H/H repulsion between the methyl groups and the hydrogen protruding from the biphenylene ring, a situation that does not occur in the anti-in conformer.
23. -1) and therefore can be considered as forbidden. In the allowed pathway, only one of the two tolyl rings becomes, alternatively, coplanar with biphenylene, whereas the other remains close to its original position: the rotation processes of the tolyl substituents are thus independent of each other.
24. Energy of the transition state for the enantiomerization (syn to syn interconversion, i.e., 90° torsion via π-barrier) is not necessarily equal to that for the interconversion of the two anti conformers: two different transition states thus imply two different π-barriers, as predicted by calculations (Table 1, Scheme 2, and Figure S-1). The pathways for the 90° torsion (π-barriers) take place through transition states where both the tolyl rings move away simultaneously from their original positions, reaching dispositions where both are tilted by the same dihedral angle with respect to biphenylene (see: TS-2 and TS-3 of Figure S-1 of the Supporting Information). The corresponding single imaginary normal modes involve the movement of both m-tolyl rings; accordingly, the 90° torsion processes should be considered examples of correlated motions. As a further indication, the computations show that situations where only one of the two tolyl groups has moved across to the nearly orthogonal position do not correspond to transition states.
25. -1 lower computed energy, as in Figure 1) is further confirmed by the computed methyl shifts that are predicted to be upfield for anti-in (1.82 ppm) with respect to anti-out (2.52 ppm): such a computed difference (0.70 ppm) agrees with the difference (0.87 ppm) observed in the experimental spectrum, where the most intense signal is likewise upfield with respect to the least intense one (1.08 and 1.95 ppm, respectively, as in the -173°C trace of Figure 3).
26. 4) is needed for describing the direct interconversion of the two enantiomers within the syn conformation (see Scheme 1).
27. -1, as in Table 1.
28. -1 should be taken into account.
29. When these types of situations are encountered in dynamic NMR processes, the effects of the higher barrier are invisible until also the lower barrier is frozen. See, for instance: (a) Jackson, W. R.; Jennings, W. B. Tetrahedron Lett. 1974, 15, 1837-1838.
30. (b) Anderson, J. E.; Casarini, D.; Ijeh, A. J.; Lunazzi, L. J. Am. Chem. Soc. 1997, 119, 8050-8057.
31. (c) Lunazzi, L.; Mazzanti, A.; Álvarez Muñoz, A. J. Org. Chem. 2000, 65, 3200-3206.
32. (a) Jackman, L. M.; Sternhell, S. Applications of NMR Spectroscopy in Organic Chemistry, 2nd ed.; Pergamon Press: Oxford, 1969; p 95.
33. (b) Jennings, W. B.; Farrell, B. M.; Malone, J. F. Acc. Chem. Res. 2001, 34, 885-894.
34. (c) Wüthrich, K. Angew. Chem., Int. Ed. 2003, 42, 3340-3363.
35. Humayun Kabir, S. M.; Hasegawa, M.; Kuwatani, Y.; Yoshida, M.; Matsuyama, H.; Iyoda, M. J. Chem Soc., Perkin Trans. 1 2001, 159-165.
36. For the preparation of the intermediate 2,2′,6,6′- tetrabromobiphenyl, see: Rajca, A.; Safronov, A.; Rajca, S.; Ross, C. R., II; Stezowski, J. J. J. Am. Chem. Soc 1996, 118, 7272-7279.
37. Leroux, F.; Schlosser, M. Angew. Chem., Int. Ed. 2002, 41, 4272-4274.
38. (a) Bradley, S. A3.; Krishnamurthy, K. Magn. Reson. Chem. 2005, 43, 117-123.
39. (b) Willker, W.; Leibfritz, D.; Kerssebaum, R.; Bermel, W. Magn. Reson. Chem. 1993, 31, 287-292.
40. Hurd, R. E.; John, B. K. J. Magn. Reson. 1991, 91, 648-653.