Synthesis of 6H,7H-chromeno[3′,4′:4,5]thieno[3,2-b]indol-6-ones using the Fischer indolization reaction.

[Display omitted] • Fused coumarin-thieno[3,2- b ]indole compounds were readily prepared in three steps. • Thieno[3,2- b ]indole part of these molecules was formed thought Fischer indolization. • The synthesis was carried out from available 4-hydroxycoumarins. A series of 6 H ,7 H -chromeno[3′,4′:4,5]thieno[3,2- b ]indol-6-ones, bearing thieno[3,2- b ]indole and coumarin parts in their fused molecules, were readily prepared using one-pot procedure based on reaction of 3-aminothieno[3,2- c ]coumarins, in situ formed from 3-aminothieno[3,2- c ]coumarin-2-carboxylates, with arylhyrazines according to the Fischer indole synthesis. In turn, the synthesis of methyl 3-aminothieno[3,2- c ]coumarin-2-carboxylates were carried out in two steps from available 4-hydroxycoumarins. To this end, 4-hydroxycoumarins were successively treated with POCl 3 -DMF complex and hydroxylamine hydrochloride to obtain 4-chloro-3-cyanocoumarins. The latter substrates further reacted with methyl thioglycolate in the presence of NaOMe to give the required 3-aminothiophene-2-carboxylate precursors. [ABSTRACT FROM AUTHOR]