Allenylphosphonates/Allenylphosphine Oxides as Intermediates/Precursors for Intramolecular Cyclization Leading to Phosphorus-Based Indenes, Indenones, Benzofurans, and Isochromenes

Utilizing internally available functional groups, a simple protocol for the efficient synthesis of phosphorus-based indenes, indenones, benzofurans, and isochromenes via intramolecular cyclization of allene intermediates/precursors is generated; the latter intermediates/precursors are conveniently obtained through aldehyde-, alkylidene-, and hydroxyl-functionalized propargyl alcohols and PIII–Cl precursors. The structures of key products have been unequivocally confirmed by X-ray crystallography.