Acknowledgment. We thank the National Institutes of Health for their generous support of our programs. JF was a Spanish Ministry of Education and Science Post- doctoral Fellow. Supplementary Material Available: X-ray crystallographic analysis of adducts 10 and 14 (14 pages). Ordering information is given on any current masthead page. ... Barry M. Trost,* Josefa Florez, Kenneth J. Haller Departments of Chemistry University of Wisconsin Madison, Wisconsin 53706, ...