An efficient [2 + 2 + 2] benzannulation of phthalic acids/anhydrides with two alkynes was developed for synthesis of multisubstituted 1-naphthoic acids via Ru-catalyzed C-H activation. The reaction preceded well using atmospheric oxygen as the sole oxidant with high atom/step economies. Facilitated by the free carboxyl group, the products can be easily converted to diverse polycyclic molecules.