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Metal sodium (1.5 g) was gradually added to ethanol (50 ml) at room temperature, followed by stirring for 5 minutes, and diethyl carbonate (8.9 ml, 73 mmol) was added thereto at room temperature. Further, a solution of ethyl 4-chlorophenylacetate (10 g) in ethanol (10 ml) was added dropwise thereto with stirring, and the stirring was continued for 2 hours. The reaction mixture was concentreated, and diethyl ether (150 ml) and 10% aqueous acetic acid (150 ml) were added to the residue for extraction. The aqueous layer was further washed with diethyl ether (50 ml). The combined organic layer was dried over magnesium sulfate and concentrated under reduced pressure. To the resulting residue were added water (25 ml) and 37% aqueous formaldehyde (8 ml) at room temperature, followed by vigorous stirring at room temperature. After addition of an aqueous solution (36 ml) of potassium carbonate (6.5 g) over 5 minutes, the mixture reaction was stirred for 4 hours and extracted with diethyl ether (100 ml×2). The extract was dried over anhydrous magnesium sulfate and concentrated under reduced pressure to give a crude product of ethyl 4-chlorophenyl-α-methyleneacetate (yield, 10 g).

1. customat room temperature
2. stirringwith stirring
3. waitthe stirring was continued for 2 hours
4. washThe aqueous layer was further washed with diethyl ether (50 ml)
5. dry with materialThe combined organic layer was dried over magnesium sulfate
6. concentrationconcentrated under reduced pressure
7. additionTo the resulting residue were added water (25 ml) and 37% aqueous formaldehyde (8 ml) at room temperature
8. stirringby vigorous stirring at room temperature
9. additionAfter addition of an aqueous solution (36 ml) of potassium carbonate (6.5 g) over 5 minutes
10. customthe mixture reaction
11. stirringwas stirred for 4 hours
12. extractionextracted with diethyl ether (100 ml×2)
13. dry with materialThe extract was dried over anhydrous magnesium sulfate
14. concentrationconcentrated under reduced pressure