Synthesis of dimethyl 3-perfluoroalkyl-4-(3-oxo-2-triphenyl-phosphoranylidenbutanylidene)-pent-2-enedioate and its cyclization

The title compounds 5a-5c were prepared via the reaction of methyl 2-perfluoroal-kynoates (4) with methyl 5-oxo-4-(triphenylphosphoranylidene)hex-2-enoate (3), which was obtained from the reaction of methyl propynate (2) with acetylmethylenetriphenylphosphorane (1) at -5-0℃. Intramolecular elimination of Ph3PO took place when compound 5 was heated in aqueous methanol at 115-120℃ in sealed tube, yielding dimethyl 2-trifluoromethyl-4-methylisophthalate (6a) from 5a and methyl 5-acetyl-4-hydroxy-2-heptafluoropropanylbenzoate (6b) from 5b, respectively. The structures of compounds 5, 6a and 6b were confirmed by IR, MS, 1H NMR, 19F NMR and 13C NMR spectroscopy and elemental analyses. Rection mechanisms for the formation of compounds 5, 6a and 6b were proposed.

Synthesis of dimethyl 3-perfluoroalkyl-4-(3-oxo-2-triphenyl-phosphoranylidenbutanylidene)-pent-2-enedioate and its cyclization

The title compounds 5a–-5c were prepared via the reaction of methyl 2-perfluoroalkynoates (4) with methyl 5-oxo-4-(triphenylphosphoranylidene)hex-2-enoate (3), which was obtained from the reaction of methyl propynate (2) with acetylmethylenetriphenylphosphorane (1) at–-5–0°C. Intramolecular elimination of Ph₃PO took place when compound 5 was heated in aqueous methanol at 115–120°C in sealed tube, yielding dimethyl 2-trifluoromethyl-4-methylisophthalate (6a) from 5a and methyl 5-acetyl-4-hydroxy-2-heptafluoropropanylbenzoate (6b) from 5b, respectively. The structures of compounds 5 , 6a and 6b were confirmed by IR, MS, ¹H NMR, ¹⁹F NMR and ¹³C NMR spectroscopy and elemental analyses. Reaction mechanisms for the formation of compounds 5 , 6a and 6b were proposed.