A novel PPh3-catalyzed (4 + n) annulation of 2-(acetoxymethyl)buta-2,3-dienoates 1c-c with 1,n-binucleophiles (n = 1, 2) has been developed to provide a facile synthetic method for cyclopentene and 1,2,3,6-tetrahydropyridazine derivatives. The acetate group of 2-(acetoxymethyl)buta-2,3-dienoate is crucial for the Formation of 1,4-biselectrophilic intermediate C, which is recognized to be a 1,4-biselectrophile that can react with 1,n-bisnucleophiles. Deuterium studies also suggest that the reaction pathway involves a proton-transfer process.