Kim, Sung-Kyu; Cho, Su-Dong; Kweon, Deok-Heon; Lee, Sang-Gyeong; Chung, Joo-Wha; Shin, Sung Chul; Yoon, Yong-Jin Journal of Heterocyclic Chemistry, 1996 , vol. 33, # 2 p. 245 - 248