To ethyl (4-methoxybenzoyl)acetate (23.0 g, 0.104 mol), prepared by the method of Krapcho et al., Org. Syn. 47, 20 (1967), and 5-(2-nitrovinyl)-1,3-benzodioxole (17.0 g, 0.088 mol) dissolved in 180 mL of toluene and heated to 80° C. was added 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU, 0.65 g) with stirring. The mixture was heated until all the nitro starting material dissolved. The solution was stirred without heating for 30 minutes and then an additional 0.65 g of DBU was added. After stirring an additional 45 minutes, thin layer chromatography (5% ethyl acetate in methylene chloride) indicated the absence of nitro starting material. Toluene (200 mL) was added, and the organic phase was washed with dilute hydrochloric acid and NaCl solution. The organic phase was dried over sodium sulfate and then concentrated under reduced pressure. The residue obtained was chromatographed on silica gel eluting with 3:1 hexane-ethyl acetate to give 21.22 g of the desired product as a mixture of isomers and 9.98 g. of recovered ethyl (4-methoxybenzoyl)acetate.
