Iron-catalyzed cascade cyclization of diaryldiyn-3-ones with P(O)H compounds: a rapid method for accessing 10-phosphorylated benzo[b]fluorenones

Abstract

A new inexpensive iron-catalyzed phosphination of diaryldiyn-3-ones under mild conditions for the synthesis of 10-phosphorylated benzo[b]fluorenones is presented. The reaction is proposed to proceed via the generation of electrophilic phosphenium species (Ar₂POTf) from secondary phosphine oxides in the presence of Tf₂O and 2,6-lutidine, followed by cycloaddition with alkynes to form three-membered phosphirenium cation intermediates. Subsequently, a rapid intermolecular tandem cyclization occurs.