1. Department of Chemistry, University of York, Heslington, York YO10 5DD, U.K., Department of Process Research, Merck Research Laboratories, Rahway, New Jersey 07065, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, S3 7HF, U.K., and Eli Lilly and Co. Ltd., Lilly Research Centre, Erl Wood Manor, Sunninghill Road, Windlesham, Surrey, GU20 6PH, U.K.