A simple and efficient base-promoted denitrogenative/deoxygenative/deformylative benzannulation is developed for the construction of biologically interesting polyfunctionalized xanthones starting from N-tosylhydrazones and two molecules of 3-formylchromones. This unprecedented protocol proceeds via a cascade diazo formation/Michael addition/denitrogenation/[4 + 2] cycloaddition/elimination/ring opening. The synthesized xanthones possess potent UV-filter, fluorescent sensor, and antioxidant properties.