A new and convenient synthetic way to 2-substituted thieno[2,3-b]indoles
Roman A Irgashev1, Arseny A Karmatsky1, Gennady L Rusinov1
1Postovsky Institute of Organic Synthesis, Ural Division of the Russian Academy of Sciences, Ekaterinburg, 620990, Russia ; Ural Federal University named after the First President of Russia, B. N. Yeltsin, Ekaterinburg, 620002, Russia.
Abstract:
A short and robust approach for the synthesis of 2-(hetero)aryl substituted thieno[2,3-b]indoles from easily available 1-alkylisatins and acetylated (hetero)arenes has been advanced. The two-step procedure includes the "aldol-crotonic" type of condensation of the starting materials, followed by treatment of the intermediate 3-(2-oxo-2-(hetero)arylethylidene)indolin-2-ones with Lawesson's reagent. The latter process involves two sequential reactions, namely reduction of the C=C ethylidene double bond of the intermediate indolin-2-ones followed by the Paal-Knorr cyclization, thus affording tricyclic thieno[2,3-b]indoles.
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