α-Halogenation of triphenylene-based discotic liquid crystals: towards a chiral nucleus

Abstract

In an attempt to prepare chiral discotic liquid crystals based on a helically twisted triphenylene nucleus a route has been developed for the introduction of α-fluoro, -chloro and -bromo substituents and it is shown that multiple α-halogenation is also possible. The monosubstituted derivatives all show enhanced mesophase stability whilst formation of the mesophase is suppressed for the polyhalogenated derivatives. Rather surprisingly, reaction of 2,3,6,7,10,11-hexahexyloxytriphenylene (HAT6) with iodine monochloride results in chlorination rather than iodination.

References

1. (a) K. Bock and W. Helfrich, Liq. Cryst., 1992, 12, 697; (b) Liq. Cryst., 1995, 18, 387; (c) X. H. Chen and G. Scherowsky, J. Mater. Chem., 1995, 5, 417.
2. (a) H. Zimmermann, R. Poupko, Z. Luz and J. Billard, Z. Naturforsch., 1986, 41A, 1137; (b) J. Malthete and A. Collet, J. Am. Chem. Soc., 1987, 109, 7544.
3. (a) J. Malthête, J. Jacques, N. H. Tinh and C. Destrade, Nature, 1982, 298, 46; (b) C. F. Van Nostrum, A. W. Bosman, G. H. Gelinck, P. G. Schouten, J. M. Warman, A. P. M. Kentgens, M. A. C. Devilliers, A. Meijerink, S. J. Picken, U. Sohling, A. J. Schouten and R. J. M. Nolte, Chem. Eur. J., 1995, 1, 171.
4. (a) N. Usol'tseva, K. Praefcke, D. Singer and B. Gündogan, Liq. Cryst., 1994, 16, 617; (b) K. Praefcke, D. Singer and A. Eckert, Liq. Cryst., 1994, 16, 53.
5. M. S. Newman and A. S. Hussey, J. Am. Chem. Soc., 1947, 69, 3023.
6. A. J. Ashe, J. W. Kampf and P. M. Savla, J. Org. Chem., 1990, 55, 5558.
7. A. H. A. Tinnemans and W. H. Laarhoven, Tetrahedron, 1979, 35, 1535.
8. (a) N. Boden, R. J. Bushby and A. N. Cammidge, Mol. Cryst. Liq. Cryst., 1995, 260, 307; (b) N. Boden, R. J. Bushby and A. N. Cammidge, Liq. Cryst., 1995, 18, 673; (c) N. Boden, R. J. Bushby, A. N. Cammidge and G. Headdock, J. Mater. Chem., 1995, 5, 2275.
9. N. Boden, R. J. Bushby, A. N. Cammidge and G. Headdock, UK Pat. GB 9505940.8, 1995.
10. N. Boden, R. J. Bushby, A. N. Cammidge and G. Headdock, Tetrahedron Lett., 1995, 8685.
11. K. Praefcke, A. Eckert and D. Blunk, Liq. Cryst., in the press.
12. (a) R. B. Sandin, W. V. Drake and F. Leger, Org. Synth., 1943, Coll. Vol. II, 196; (b) G. H. Woollet and W. W. Johnson, Org. Synth., 1943, Coll. Vol. II, 343.
13. D. E. Turner, R. F. O'Malley, D. J. Sardella, L. S. Barinelli and P. Kaul, J. Org. Chem., 1994, 59, 7335.
14. (a) P. R. Birkett, A. G. Avent, A. D. Darwish, H. W. Kroto, R. Taylor and D. R. M. Walton, J. Chem. Soc., Chem. Commun., 1993, 1230; (b) J. Chem. Soc., Chem. Commun., 1995, 683.
15. (a) N. Boden, R. C. Borner, D. R. Brown, R. J. Bushby and J. Clements, Liq. Cryst., 1992, 11, 325; (b) N. Boden, R. J. Bushby, J. Clements and R. Luo, J. Mater. Chem., 1995, 5, 1741.
16. Y. Kita, H. Tohma, K. Hatanaka, T. Takada, S. Fujita, S. Mitoh, H. Sakurai and S. Oka, J. Am. Chem. Soc., 1994, 116, 3684.
17. (a) N. Boden, R. J. Bushby and A. N. Cammidge, J. Chem. Soc, Chem. Commun., 1994, 465; (b) N. Boden, R. J. Bushby, A. N. Cammidge and G. Headdock, Synthesis, 1995, 31.
18. (a) G. W. Gribble and W. J. Kelly, Tetrahedron Lett., 1985, 26, 3779; (b) I. D. Rae, A. Staffa, A. C. Diz, C. B. Giribet, M. C. Ruiz de Azua and R. H. Contreras, Aust. J. Chem., 1987, 40, 1923; (c) I. D. Rae, J. A. Weigold, R. H. Contreras and G. Yamamoto, Magn. Reson. Chem., 1992, 30, 1047.