Convenient synthesis of 4-perfluoroalkyl-6-(2-naphthyl)-2-pyranones

In the presence of K2CO3, reaction of (2-naphthoyl)methyltriphenylphosphonium bromide (1) with methyl 2-perfluoroalkynoates (2) in CH2Cl2 at room temperature gave methyl 4-(2-naphthoyl)-2-triphenylphosphoranylidene-3-perfluoroalkyl-3-butenoates (3) as major products and methyl 4-(2-naphthoyl)-4-triphenylphosphoranylidene-3-perfluoroalkyl-2-butenoates (4) as minor products in excellent yields. 4-Perfluoroalkyl-6-(2-naphthyl)-2-pyranones (5) were obtained in high yield by hydrolysis of the methylene phosphoranes (3) in hot aqueous methanol in a sealed tube. The structures of compounds 3, 4, and 5 were confirmed by IR, MS, 1H, 19F and 13C NMR, and microanalyses. Reaction mechanisms are proposed to account for the formation of products 3, 4, and 5.