3-(2,3-Dihydro-1,4-benzodioxin-6-yl)acrylic acid

1), glycine ethyl ester hydrochloride (28g, 0.2mol) dissolved in 30mL of water, add 100mL of dichloroethane, cooled down to -15 , dropwise addition of sodium nitrite (15.2g, 0.22mol) dissolved in 20mL of water to the solution obtained from the drop, 30min dropwise, then dropwise addition of hydrochloric acid with a mass concentration of 15% of the solution adjusted to pH = 4, at -15 continue to react for 2h! After adding saturated sodium carbonate solution to pH=6, static liquid separation, take the organic phase in the lower layer of cooling for use; the organic phase is the dichloroethane solution of ethyl diazoacetate.

2), 1,2-methylenedioxybenzene (8.13g, 0.067mol) was dissolved in 40mL of dichloroethane, then added 0.5g of cuprous chloride, heated to 60 , dropwise addition of ethyl diazoacetate dichloroethane solution obtained in step 1 (containing 0.14mol of ethyl diazoacetate), 6h dropwise completion. After dropwise completion, the reaction was continued at 60C for 1h and then cooled to room temperature, after desolventizing the dichloroethane, the fraction at 100C-110C, i.e., ethyl 1,4-benzodioxane-6-propenoate, was collected by distillation under reduced pressure at 30 Pa.

3), all of the above prepared 1,4-benzodioxane-6-acrylic acid ethyl ester was added to the solution obtained by dissolving NaOH (8 g, 0.2 mol) in 50 mL of water, and the temperature was raised to 80 C. After hydrolysis reaction for 2h, the solution was adjusted to pH=6 by hydrochloric acid with a mass concentration of 15% and then filtered, and the resulting brownish-yellow solid was recrystallized in ethanol (20 ml) to get White solid - 1,4-benzodioxane-6-propenoic acid 10.5g, mp.125-127C, yield 87.1%.