Aromatic organophosphorus compounds have significant applications in catalysis, organic synthesis, medicinal chemistry, and materials science. Herein, we report a metal-free, Et3N-mediated phosphorylation of 4-nitroisoxazoles with secondary phosphine oxides. The protocol proceeds via a unique dearomatization-elimination process, affording functionalized phosphonylated isoxazoles with good yields under mild conditions. Furthermore, some other aromatic substrates, including nitrofuran, nitroindole, nitrothiophene and nitroquinoxaline derivatives, can also undergo this reaction to afford the corresponding phosphonylated heteroarenes. Gram-scaled synthesis and synthetic transformations further suggest that this methodology has practical applicability and synthetic value. Additionally, we successfully synthesized novel phosphonylated enaminones via a one-pot cascade dearomatization/elimination/reductive ring-opening process.