*Organic Chemistry Laboratory, Swiss Federal Institute of Technology, ETH-Zentrum, CH-8092, Zurich, Switzerland
#School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
%Daresbury Laboratory, Warrington, Cheshire WA4 4AD, U.K.
+Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
Article: J. Amer. Chem. Soc. 1998, 120, 13274-13275.