Visible-light-induced cycloisomerization of O-tethered 1,6-enynes to phosphinylated 3,6-dihydropyrans

Phosphorus-substituted heterocycles are core motifs in a large amount of biologically active compounds. In this research, a photocatalytic cycloisomerization of O-tethered 1,6-enynes with diarylphosphine oxides under a visible-light irradiation has been achieved. This method provides rapid and efficient access to phosphinylated heterocycles (27 examples) with good functional group compatibility under mild conditions. Spectroscopic studies suggest that a reductive quenching of the excited photocatalyst Ir(III)* with diarylphosphine oxides generates phosphinyl radicals, which undergo a tandem radical cyclization of O-tethered 1,6-enynes to afford the desired phosphinylated 3,6-dihydropyrans.