Synthesis of hybrid polycycles containing fused hydroxy benzofuran and 1H-indazoles via a domino cyclization reaction†
A stoichiometry controlled domino cyclization reaction of hydrazone and p-benzoquinone to an angularly fused 3H-benzofuro[3,2-e]indazole core with an embedded oxygenated dibenzofuran framework under mild reaction conditions is disclosed. The reaction involves palladium catalyzed 5-hydroxy-1H-indazole formation followed by TFA mediated [3+2] annulation between the in situ formed 5-hydroxy-1H-indazole and p-benzoquinone. The developed method is attractive because of the concomitant formation of two heterocyclic rings with consecutive multiple bond forming events that include two C–C, one C–N and one C–O bonds. Spectroscopic and theoretical studies of the blue emissive benzofuroindazole derivatives have also been described.