1. Institute of Chemistry, University of Tartu, 14A Ravila, Tartu 50411, Estonia, Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, Florida, 32611, Department of Chemistry, Tallinn University of Technology, Akadeemia tee 15, Tallinn 12618, Estonia, and Department of Chemistry, University of North Texas, Denton, Texas 76203-5070