1. Hearn, M.J. and Swanson, S.L., J. Heterocycl. Chem., 1981, vol. 18, p. 2007.
2. Cortes, E., Martinez, R., Avila, J.G., and Toscano, R.A., J. Heterocycl. Chem., 1988, vol. 25, p. 895.
3. Dostal, J. and Potacek, M., Collect. Czech. Chem. Commun., 1990, vol. 55, p. 2840.
4. Olugbade, T.A., Waigh, R.D., and Mackay, S.P., J. Chem. Soc., Perkin Trans. 1, 1990, p. 2657.
5. Pyrko, A.N., Khim. Geterotsikl. Soedin., 1990, p. 1693.