A facile and efficient synthesis of thieno[2,3-c]furans and furo[3,4-b]indoles via a Pummerer-induced cyclization reaction

Several thieno[2,3-c]furans and furo[3,4-b]indoles with polyheterocyclic ring systems were synthesized by utilizing tandem Pummerer-Diels-Alder reaction sequence. The sequence utilizes alpha-thioisobenzofurans as key intermediates in the cascade process which forms 4+2-cycloadducts when combined with a specific dienophile. The tandem-cascade process exhibited intramolecular variation on the thiophene series during the subsequent reactions.