Efficient three-component synthesis of tetrahydrothieno[3,2-f]quinolines

An efficient one-pot method for the synthesis of tetrahydrothieno[3,2-f]quinolines is described, using the imino Diels–Alder reaction between ethyl-5-aminobenzothiophene-2-carboxylate, aromatic aldehydes and cyclic enol ethers. Furthermore, hydroxyalkyl-substituted tetrahydrothieno[3,2-f]quinolines were synthesized in good yields, by performing the same imino Diels–Alder reaction in absence of aldehydes. The intramolecular aza-Diels–Alder reaction of 5-aminobenzothiophene with o-(allyloxy)benzaldehyde was also performed resulting in the fully oxidized thienoquinoline derivative.