It has been established that an in situ-generated cationic platinum(II)/rac-BINAP complex catalyzes the intramolecular dearomative 5-endo spirocyclization of N-(methylnaphthalenyl)propiolamides via the deprotonation-protonation sequence (formal aromatic ene reaction). Mechanistic studies revealed that our previously reported dearomative 6-endo cyclization followed by the Friedel-Crafts reaction is kinetically and thermodynamically unfavored, and thus, the 5-endo spirocyclization proceeds selectively.