Reduction of diaryl alkenes by hypophosphorous acid–iodine in acetic acid

A mixture of 50% aqueous H3PO2 and I2 (in catalytic amount) in HOAc efficiently reduces aryl alkenes to the corresponding alkanes in high yield. Addition of acetic anhydride to the medium results in ring-acetylation (or N-acetylation in the case of amines). H3PO2 costs only one-fifth as much as hydriodic acid on a mole basis and one mole of H3PO2 produces four moles of HI, resulting in a 20-fold cost advantage for H3PO2/I2 over aqueous HI as a source of HI.