1. Department of Chemistry, University of Wroclaw, 14 F. Joliot-Curie, Wroclaw, Poland, and Institut für Organische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Henkestrasse 42, 91054 Erlangen, GermanyThis is a Chemical Reviews Perennial Review. The root paper of this title was published in Chem. Rev. 2003, 103, 4175. Updates to the text appear in red type. Structures added to the charts are within blue boxes.