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.