2-(Acetoxymethyl)buta-2,3-dienoate, a Versatile 1,4-Biselectrophile for Phosphine-Catalyzed (4 + n) Annulations with 1,n-Bisnucleophiles (n = 1, 2)

Abstract

A novel PPh₃-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.