The highly electrophilic fluorophosphonium cation [(C6F5)3PF]+[B(C6F5)4]− is shown to catalyze Diels–Alder reactions of challenging dienophile/enophile combinations and Nazarov cyclizations of various precursors. Several other electrophilic phosphonium cations (EPCs) have been tested for comparison. This systematic study demonstrates the power of these Lewis acids to act as catalysts for synthetically useful pericyclic reactions.