1. D. Kästner, Angew. Chem.,54, 296 (1941).
2. W. Ried and W. Bodenstein, Tetrahedron Lett., 247 (1962).
3. S. P. Starkov and A. I. Panasenko, Zh. Obshch. Khim.,7, 1463 (1971).
4. I. P. Kovalev and E. V. Titov, Zh. Obshch. Khim.,33, 1670 (1963).
5. L. J. Bellamy, The Infra-Red Spectra of Complex Molecules, Methuen, London (1958).