Facile Access to Phospholene Fused Polycycles through Intramolecular Alder‐ene Reaction of Phosphole Sulfides

We have developed a simple, metal‐free annulation of phosphole sulfides through intramolecular Alder‐ene reaction involving a 1,6‐enyne component. This atom‐efficient cyclization pathway provides phospholene fused polycycles with high yields and excellent regioselectivity. The 1,6‐enyne cyclization of phosphole sulfides with a tethered phenyl group affords structurally complex benzo‐fused bicyclo[3.3.0] scaffolds. Meanwhile, phosphole sulfides with a naphthyl group produce naphtho‐fused bicyclo[4.3.0] skeletons, as well as structurally complex [2+2] cycloaddition products.