1. W. L. Mosby, Heterocyclic Systems with Bridgehead Nitrogen Atoms, Interscience, New York, Vol. 1, p. 239 (1961).
2. H. L. Blewitt in: A. Weissberger and E. C Taylor (editors), Special Topics in Heterocyclic Chemistry,Wiley, New York, p. 117 (1977).
3. E. E. Glover and M. Yorke, J. Chem. Soc. C, 3280 (1971).
4. T. Pyl, R. Giebelmann, and H. Beyer, Liebigs Ann. Chem., 643, 145 (1961).
5. N. O. Saldabol and Yu. Yu. Popelis, Khim. Geterotsikl. Soed., 691 (1972). [Chem. Heterocycl. Comp., 8, 627 (1972)].