2-(Acetoxymethyl)buta-2,3-dienoate, a versatile 1,4-biselectrophile for phosphine-catalyzed (4 + n) annulations with 1,n-Bisnucleophiles (n = 1, 2).

A novel PPh(3)-catalyzed (4 + n) annulation of 2-(acetoxymethyl)buta-2,3-dienoates 1c-e with 1,n-bisnucleophiles (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.