Regioselective Diels-Alder cycloadditions and other reactions of 4,5-, 5,6-, and 6,7-indole arynes.
The regioselectivity of Diels-Alder cycloadditions of indole arynes (indolynes) at all three benzenoid positions was examined. Cycloadditions with the 4,5-and 5,6-indolynes, derived via metal-halogen exchange from the corresponding o-dibromo indoles, showed essentially no selectivity with 2-t-butylfuran. In contrast, the 6,7-indolyne displayed virtually complete preference for the more sterically congested cycloadduct. This same cycloadduct undergoes a facile acid-catalyzed rearrangement to afford the annulated enone, or alternatively, undergoes hydrolysis and oxidation in the presence of air to give the indolobenzoquinone. The 5,6-difluoroindoles show anomolous behavior and give either 5-fluoro-6,7-indolynes with n-BuLi in ether, or 5,6-indolynes with n-BuLi in toluene. We have also demonstrated that benzenoid indolynes can be easily and conveniently generated by the fluoride-induced decomposition of o-trimethylsilyl triflates.
Department of Chemistry, University of Missouri-Kansas City, 205 Spencer Chemical Laboratories, 5100 Rockhill Road, Kansas City, MO, 64110, USA.
Neil
N
Brown
Diheng
D
Luo
David
D
Vandervelde
Shaorong
S
Yang
Allen
A
Brassfield
Keith R
KR
Buszek