1) A. Sugimoto, S. Furuyama, H. Inoue, and E. Imoto, Nippon Kagaku Kaichi, 1974, 1289.
2) A. Sugimoto, K. Inoue, H. Inoue, and E. Imoto, Nippon Kagaku Kaichi, 1974, 1294.
3) A. Sugimoto, S. Kato, H. Inoue, and E. Imoto, Nippon Kagaku Kaichi, 1974, 1299.
4) A. Sugimoto, S. Furuyama, H. Inoue, and E. Imoto, Nippon Kagaku Kaichi, 1974, 1814.
5) A. Albert, “Current Trends in Heterocyclic Chemistry,” ed. by A. Albert, G. M. Badger, and C. W. Shoppee, Butterworths Scientific Publications, London (1958), p. 20.