1. a Institute of Organic Chemistry , Martin-Luther-University Halle-Wittenberg , Geusaer Straβe, D-06217 Merseburg, Germany
2. b Institute of Organic Chemistry , Martin-Luther-University Halle-Wittenberg , Geusaer Straβe, D-06217 Merseburg, Germany
3. c Institute of Organic Chemistry , Martin-Luther-University Halle-Wittenberg , Geusaer Straβe, D-06217 Merseburg, Germany
4. d Institute of Organic Chemistry , Martin-Luther-University Halle-Wittenberg , Geusaer Straβe, D-06217 Merseburg, Germany
5. e Institute of Organic Chemistry , Martin-Luther-University Halle-Wittenberg , Geusaer Straβe, D-06217 Merseburg, Germany