Oxidant‐Expedited Synthesis of H‐Phosphonates

A new oxidant‐expedited method has been developed that enables synthesis of H‐phosphonates from phosphites using extremely mild oxidants (e.g., air or O 2 ). H‐phosphonates are key building blocks in organophosphorus chemistry due to their multimodal reactivity patterns, which make them versatile reagents in many fields in synthetic chemistry. Using the methodology outlined herein, very high conversions (>85%) were achieved in the formation of a variety of H‐phosphonates for reactions using pure O 2 as the oxidant, while reactions in which air was employed as the oxidant also resulted in very high conversions (>92%) except in two very challenging cases involving hydrolytically sensitive products. Unequivocal evidence demonstrating that the transformations are expedited by the presence of oxidants is provided. Along with this, evidence derived from various mechanistic experiments supports the operation of a radical‐based mechanism in which water supplies both the hydrogen and the oxygen that become incorporated into the H‐phosphonate product in the new PH and PO bonds. The methodology reported herein employs acid‐free conditions, requires only phosphite, water, and O 2 as reagents, and is thus an exceptionally mild method for accessing a variety of H‐phosphonate products.