TETRAHEDRON LETTERS, vol. 33, no. 45, page. 6811 - 6814, 1992-11-03
BULLETIN OF THE KOREAN CHEMICAL SOCIETY, vol. 13, no. 3, page. 343 - 344, 1992-06-20
TETRAHEDRON LETTERS, vol. 33, no. 18, page. 2557 - 2560, 1992-04-28