1. Department of Organic Chemistry, Stockholm University, 10691 Stockholm, Sweden
2. Department of Chemistry, BMC, Uppsala University, P.O. Box 576, 75123 Uppsala, Sweden
3. Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, P. R. China
4. Department of Chemistry, University College of Science, University of Calcutta, 92, A. P. C. Road, Kolkata 700009, West Bengal, India