Nonclassical Bergman Cyclization of Enediynes ： Synthesis of Dibenzofurans and Carbazoles

1. Nonclassical Bergman Cyclization of Enediynes： Synthesis of Dibenzofurans and Carbazoles Chia-Ying Lee, Chi-Fong Lin, Ching-Chen Chiu, and Ming-Jung Wu* Faculty of Medicinal and Applied Chemistry, and Graduate Institute of Pharmaceutical Sciences, Kaohsiung Medical University, Kaohsiung, Taiwan Abstract Recently, we found that treatment of 2-(6-substituted 3(Z)-henxen-1,5-diynyl)phenyl t-butyldimethylsilyl ethers 1 with sodium methoxide in refluxing methanol gave dibenzofurans 2 in excellent yield.1 The aniline analogs 3 have also been carried out to test the anionic cycloaromatization of enediynes and we found that treatment of 3 with potassium t-butoxide in NMP at 60 oC gave the carbazole 4 in 45-86 % yields.2 ( Eq 1 ) ( Eq 2 ) Part A Synthesis of Dibezofuran Part B Synthesis of Carbazole Reference： 1. Wu, M. J.; Lee, J. Y.; Lin, C. F. Angew. Chem., Int. Ed. 2002, 41, 4077 2. Lee, C.-Y.; Lin, C.-F.; Lee, J.-L.; Chiu, C.-C.; Lu, W.-D.; Wu, M.J.; J. Org. Chem.; 2004, 69, 2106-2110