Synthesis of 2H-1,2-Oxaphosphorin 2-Oxides via Ag₂CO₃-Catalyzed Cyclization of (Z)-2-Alken-4-ynylphosphonic Monoesters

[reaction: see text]. Six new 2-ethoxy-2H-1,2-oxaphosphorin 2-oxides were synthesized with high regioselectivity in good yields via Ag(2)CO(3)-catalyzed cyclization of (Z)-2-alken-4-ynylphosphonic monoesters in CH(2)Cl(2) at room temperature. This cyclization of P-OH to substituted alkynes is reported for the first time. The products are a class of phosphorus heterocycles with potential use and are heretofore prepared with difficulty.