TETRAHEDRON LETTERS, vol. 39, no. 35, page. 6321 - 6322, 1998-08-27
JOURNAL OF ORGANIC CHEMISTRY, vol. 62, no. 20, page. 7047 - 7048, 1997-10-03
TETRAHEDRON LETTERS, vol. 33, no. 44, page. 6661 - 6664, 1992-10-27