Regio- and Stereoselective Alkenylation of Allenoates with gem-Difluoroalkenes: Facile Access to Fluorinated 1,4-Enynes Bearing an All-Carbon Quaternary Center.

A regio- and stereoselective synthesis of fluorinated 1,4-enynes bearing an all-carbon quaternary center at the propargylic position is developed. The synthesis starts from readily available allenoates and gem-difluoroalkenes and proceeds via a key alkynylenolate intermediate following a nucleophilic addition/β-F elimination. This reaction occurs under mild reaction conditions with good tolerance to a variety of functional groups. Synthetic utility is demonstrated by further transformations of the products. Furthermore, the reaction can also be applied for the synthesis of α-alkenyl allenoates by using 3,3-disubstituted allenoates.