1. Hilgetag, G. and Martini, A. 1972., 597New York: John Wiley and Sons. C. Bachand, H. Driguez, J. M. Paton, D. Touchard and J. Lessard, J. Org. Chem., 3136(1974);
2. H. Beyer and J. Korosi, Chem. Ber., 480(1961);
3. E. Jeffreys, Am. Chem. J., 14(1899);
4. P. Radlick and L. R. Brown, Synthesis, 290(1974)