Serendipitous synthesis of phenanthrene derivatives by exploiting electrocyclization during thermolysis of Diels–Alder intermediate dihydrodibenzothiophene-S,S-dioxides

Abstract

The Diels–Alder reaction of tetraaryl cyclopentadienones with benzo[b]thiophene-S,S-dioxides in nitrobenzene under reflux led to the formation of aryl/hetero-aryl fused phenanthrene derivatives via SO₂ elimination of the intermediate dihydrodibenzothiophene-S,S-dioxides followed by 6π-electrocyclization and subsequent aromatization. The 6π-electrocyclization methodology was found to be applicable for assembling a wide variety of phenanthrene derivatives in good to moderate yields.