1. A. Hantzsch, Ber,25, 708 (1892); A. Hantzsch and A. Werner, Ber.23, 24 (1890).
2. E. Borello and M. Colombo, Gazz. Chim. Ital.,87, 615 (1957).
3. H. E. Ungnade, G. Fritz, and L. W. Kissinger, Tetrahedron,19, 235 (1963).
4. C. Pigenet, J. Armand, and H. Lumbroso, C. R. Acad. Sci. Ser. C. 1,275, 63 (1972).
5. G. J. Karabatsos and R. A. Taller, Tetrahedron,24, 3347 (1968).