358738-70-2Relevant academic research and scientific papers
Synthesis of new methylated thieno[2,3-a] and [3,2-b]carbazoles by reductive cyclization of 6-(2′-nitrophenyl)benzo[b]thiophenes obtained by palladium-catalyzed cross-coupling
Ferreira,Queiroz,Kirsch
, p. 749 - 754 (2001)
The synthesis of new methylated thieno[2,3-a] and [3,2-b]carbazoles (5) (R=H) was achieved by a palladium-catalyzed cross-coupling, intramolecular reductive cyclization sequence of reactions. The cyclization precursors 6-(2′-nitrophenyl)benzo[b]thiophenes (3) were obtained by Suzuki cross-coupling of 6-boronated methylbenzo[b]thiophenes intermediates (2) with 2-bromo or iodonitrobenzene. The boronated intermediates (2) were prepared via bromine-lithium exchange followed by boron transmetalation and coupled in situ using Pd(OAc)2 giving thus a one-pot three steps reaction from the 6-bromobenzo[b]thiophenes (1) to the cyclization precursors (3). In the reductive cyclization step, N-ethylthienocarbazoles (5) (R=Et) were also obtained. Several experiments have been made varying the amount of triethylphosphite and the time of reaction, to avoid their formation.
