Atmosphere-Controlled Regio- and Stereoselective Oxy- and Hydrophosphorylation of Alkynes Using Polyoxomolybdate as a...

Atmosphere-controlled oxyphosphorylation and hydrophosphorylation of terminal alkynes have been achieved with a polyoxomolybdate ([N(C₄H₉)₄]₂[Mo₆O₁₉]) as a heterogeneous photosensitizer. The reactions can smoothly occur under mild conditions, furnishing various β-ketophosphine oxides under air atmosphere and Z-alkenylphosphine oxides under Ar atmosphere, both in good to excellent yields and with excellent regioselectivity and stereoselectivity. The control experiments revealed that the difunctionalization reactions followed a P-centered radical addition pathway. For oxyphosphorylation transformation, oxygen in the air acted as a green oxidant and was the source of the oxygen atom in the skeleton. For hydrophosphorylation process, a "borrowing hydrogen" mechanism was reasonably proposed, the hydrogen atom adjacent to the aromatic ring originated from P(O)H compounds, exhibiting 100% atom utilization. Moreover, this polyoxomolybdate exhibited excellent stability and reusability after six turns of reactions and showed gram-scale reactivity and photocatalytic performance under solar irradiation. The developed protocol represents the first example of Lindquist-type polyoxomolybdate that serves as a highly efficient hydrogen atom transfer (HAT) photocatalyst for oxyphosphorylation and hydrophosphorylation of alkynes.