1. Key Laboratory of Organic Synthesis of Jiangsu Province; College of Chemistry; Chemical Engineering and Materials Science; Soochow University; 199 Ren-Ai Road, Suzhou Jiangsu 215123 People's Republic of China
2. Key Laboratory of Synthetic Chemistry of Natural Substances; Shanghai Institute of Organic Chemistry; Chinese Academy of Sciences; 345 Lingling Road Shanghai 200032 People's Republic of China