Saha, Ashis K.; Schairer, Wayne; Waychunas, Cheryl; Prasad; Sardaro, Mark; Upso, Donald A.; Kruse, Lawrence I. Tetrahedron Letters, 1993, vol. 34, # 38 p. 6017 - 6020 doi: 10.1016/50040-4039(00)61716-1