A cascade of styrylynols promoted by MnO2 allows the synthesis of fused tricycles with a naphthalene core. The reaction occurs under ambient conditions, offering a practical synthetic tool because of the inexpensive and abundant manganese species. The method affords products through the sequential oxidation of a propargyl alcohol, stepwise Diels-Alder cyclization, and finally rearomatization. According to density functional theory, the usually unfavorable stepwise Diels-Alder mechanism is instead a general tool for eliciting otherwise challenging dearomative annulation.