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

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 SO 2 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. The Diels-Alder adducts, dihydrodibenzothiophene- S , S -dioxides, underwent SO 2 elimination followed by thermal electrocyclization and subsequent aromatization to afford aryl/hetero-aryl fused phenanthrene derivatives.