1. Yu. I. Tarnopol'skii and V. N. Belov, KhGS [Chemistry of Heterocyclic Compounds], 651, 1965.
2. Yu. I. Tarnopol'skii and V. N. Belov, ZhOrKh, 595, 1965.
3. Yu. I. Tarnopol'skii and V. N. Belov, KhGS [Chemistry of Heterocyclic Compounds], 648, 1965.
4. F. Semmler and E. Asher, Ber.,42, 2355, 1909.
5. I. M. Seidov, A. A. Bakhshi-Zade, I. M. Chernikov, and Z. M. Melikova, Azerb. khim. Zh.,5, 57, 1962.