Methyl Acrylate → 1,5-Dimethyl 2-methylenepentanedioate

To a solution of 2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo(3,3,3)indecane (4.62 g) in tetrahydrofuran (180 ml) was added dropwise a solution of methyl acrylate (40.5 ml) in tetrahydrofuran (20 ml) at room temperature, and then the mixture was stirred overnight. This reaction solution was concentrated under reduced pressure, and then diisopropyl ether, n-hexane and chloroform were added to the resulting residue, and the mixture was again concentrated under reduced pressure. To the precipitated solid was added diisopropyl ether, the mixture was stirred, and then the insoluble substance was filtered off. The filtrate was concentrated under reduced pressure, and the resulting residue was purified by silica gel column chromatography (eluent: n-hexane/ethyl acetate=9/1 to 4/1) to give the titled compound (19.2 g).