1. The Department of Chemistry and Molecular Biology, North Dakota State University, Fargo,North Dakota 58105
2. The Department of Chemistry, Columbia University, New York,New York 10027
3. Joint Science Department, W.M. Keck Science Center, 925 North Mills Avenue,Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, California 91711
4. Institute für OrganischeChemie, Universität Würzburg, D-97074 Würzburg, Germany
5. The Department of Chemistry, University of Puerto Rico, Facundo Bueso 110, Rio Piedras, Puerto Rica 00931