1. Contribution from the Department of Organic Chemistry “A. Mangini”, University of Bologna, Via San Donato 15, 40127, Bologna, Italy; Department of Chemical Sciences and ITM-CNR, Padova Section, University of Padova, via Marzolo 1, 35131 Padova, Italy; and Department of Chemical Sciences University of Trieste, via L. Giorgieri 1, 34127 Trieste, Italy