1. U.S. Naval Research Laboratory, 4555 Overlook Avenue, SW, Washington, DC 20375, Department of Chemistry, Loyola University, 6363 St. Charles Avenue, New Orleans, Louisiana 70118, Department of Chemistry, Howard University, 525 College Street, N. W., Washington, DC 20059, and Nantes Atlantique Universités, CNRS, UMR 6513, Laboratoire de Synthèse Organique, Faculté des Sciences et des Techniques, 2, rue de la Houssinière, BP 92208, 44322 Nantes Cedex 3, France