The Effect of a Hydroxy Protecting Group on the PtCl2-Catalyzed Cyclization of Dienynes—A Novel, Efficient, and Selective Synthesis of Carbocycles Acknowledgement is made to the EU for the COST D12 Action “Cascade Free Radical Reactions” and for a short-term scientific mission to Madrid (EM). We thank Nieves Arroyo (CSIC) for preliminary experiments, Dr. J. Vaissermann (UPMC) for the X-ray analysis of 3 e, Dr. M. L. Jimeno (CNQO) for NMR studies on 3 a, Dr. M.-N. Rager (ENSCP) for NMR studies on 3 h, 6, and 11, and Matthieu Bernard (UPMC) for performing some of the experiments. We also thank Dr. Emmanuel Lacôte and Dr. Henri Rudler (UPMC) for helpful discussions.