Nonclassical Bergman Cyclization of Enediynes:

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