A novel and practical approach to monosubstituted phosphinic acid (alkylphosphonous acid) derivatives from hypophosphite salts or esters is described. Phosphorus-centered radical formation is initiated with Et3B/O2, and the reaction is conveniently conducted at room temperature in an open flask. In contrast to previously reported conditions for the radical reaction of hypophosphorous acid and sodium hypophosphite (peroxide initiators, ...