Synthesis of benzo[b]thieno[2,3-c]quinolines via palladium-catalyzed ring-closing reaction

Benzo[b]thieno[2,3-c]quinolines were synthesized via Pd-catalyzed ring closure reaction of the α-aminophosphonates obtained by the Kabachnik–Fields condensation of benzo[b]thiophene-2-carboxaldehydes, 2-iodoanilines and diethyl phosphite or dibenzyl phosphite. The intramolecular cyclizations remained incomplete under the conditions applied. The products were isolated in 11–42% yields, and the unreacted starting materials were recovered from the reaction mixture.