Derivatives of ethyl acetoacetate.

The organic compound ethyl acetoacetate (EAA) is mainly used as a chemical intermediate in the production of a wide variety of compounds, such as amino acids, analgesics, antibiotics, antimalarial agents, antipyrine and aminopyrine, and vitamin B1; as well as the manufacture of dyes, inks, lacquers, perfumes, plastics, and yellow paint pigments. Alone, it is used as a flavoring for food.

  Synthesis of derivatives of ethyl acetoacetate.

 

1.

A mixture of ethyl acetoacetate, magnesium, EtOH, CCl4 and toluene was stirred under argon at rt for 30 min. The mixture was refluxed for 1h and the cooled to 0-5 deg C. The acylating agent was added dropwise to the solution, and solution was stirred at rt for 1h. The resulting mixture was re-cooled to 0-5 deg C, and washed with 5% aq. HCl and satd NaHCO3 and brine. The organic layer was dried over MgSO4 and concentrated to give pale yellow liquids.

2.

A round-bottomed flask is charged with ethyl acetoacetate, p-acetamidobenzenesulfonyl azide and acetonitrile. The reaction vessel is cooled in an ice bath, and triethylamine is added to the stirring mixture in one portion. The reaction mixture is warmed to room temperature and stirred for 12 hr. The solvent is removed under reduced pressure, and the residue is triturated with 1:1 mixture of ether/petroleum ether. The mixture is filtered to remove the sulfonamide by-product, and the filtrate and wash are concentrated under reduced pressure. The crude product is purified by chromatograpy on silica gel with ether/petroleum ether (1:4) as eluant to yield ethyl diazoacetoacetate (yield,91%) as yellow oil.

3.

In a three-necked flask fitted with dropping funnel, a thermometer, and a mechanical stirrer, and connected to a gas-absorption trap, is placed ethyl acetoacetate. Sulfuryl chloride is added slowly with stirring and external cooling, the temperature being maintained between 0 deg C and 5 deg C. About 3 hours is required for the addition. The solution is allowed to stand overnight at room temperature, and hydrogen chloride and sulfur dioxide are removed at 40–50 deg C under water-aspirator vacuum. The residual dark-amber liquid is distilled through a short Vigreux column at reduced pressure. After a small fore-run, the ethyl α-chloroacetoacetate distils at 85–89°/17 mm. The yield of colorless liquid is 93–97%.

4.

To a solution of ethyl acetoacetate in THF at 0 deg C was added sodium hydrideportionwise. The reaction mixture was stirred for 30 min, and 2-bromoacetophenone in THF was added dropwisely. After warming the mixture to room temperature, it was stirred for 4 h. The resulting solution was quenched with water and normal work-up was conducted with diethyl ether. The organic layer was dried with MgSO4, and purified by silica gel column chromatography (EtOAc/ Hex = 1:5) to produce the desired compound as light yellow color oil.

Ethyl 2-acetyl-4-oxo-4-phenylbutanoate was treated with NH4OAc in acetic acid at room temperature. After stirring 10 min, the reaction mixture was heated to 80 deg C for overnight. After cooling to room temperature, acetic acid was evaporated under reduced pressure and subsequently water was added. The organic layer was separated and the aqueous layer was extracted with diethyl ether. Purification by normal phase preparative LC provided the desired compound as yellow solid.

5.

In a 3-l. three-necked flask provided with a stirrer and surrounded by an ice bath are placed ethyl acetoacetate and glacial acetic acid. To this solution is then added dropwise with stirring a solution of sodium nitrite in water. The rate of addition is controlled so that the temperature does not rise above 12 deg C. After the sodium nitrite solution has been added, the mixture is stirred an additional 2–3 hours. It is then allowed to warm up to room temperature and stand about 12 hours, after which acetylacetone is added at one time.
To the reaction mixture zinc dust is added in portions with vigorous stirring. The rate of addition is regulated so that the temperature never rises above 60 deg C. After the addition is complete , the mixture is refluxed for 2–3 hours on a hot plate until the unreacted zinc dust collects in balls. The hot solution is then poured through a fine copper sieve, with stirring, into ice water. The crude product which separates is contaminated with zinc. On recrystallization from 95% ethanol, 2,4-dimethyl-3-acetyl-5-carbethoxypyrrole (m.p. 143–144°) is obtained (55–60% based on the ethyl acetoacetate used) .

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