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Enantioselective Mukaiyama-Michael Reaction of β,γ-Unsaturated α-Keto Esters with Silyl Ketene Acetals Catalyzed by a Chiral Magnesium Phosphate

Hualing He, Xizhe Shen, Xinying Ding and Jon C. Antilla*

*Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou, Zhejiang Province 310018, P. R. China, Email: jantillazstu.edu.cn

H. He, X. Shen, X. Ding, J. C. Antilla, Org. Lett., 2023, 25, 782-787.

DOI: 10.1021/acs.orglett.2c04277



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Abstract

A chiral magnesium BINOL-derived phosphate catalyzes an efficient and highly enantioselective Mukaiyama-Michael reaction of silyl ketene acetals with β,γ-unsaturated α-keto esters. The resulting functionalized 1,5-dicarbonyl adducts are obtained in high yields and with excellent enantioselectivities under mild conditions.

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proposed mechanistic pathways



General procedure for asymmetric Mukaiyama-Michael reaction of β,γ-unsaturated α-keto esters

To a test tube was weighted 40 mg Molecular Sieves (4), 4.7 mg Mg[ligand]2 (2.5 mol%), 0.1 mmol β,γ-unsaturated α-keto ester, followed by 2 mL of toluene. The mixture was cooled to -30 C, then 0.15 mmol of silyl ketene acetal was added via micro syringe. The mixture was stirred for 1 hour, after which toluene was removed and replaced by 1.0 mL of THF. 0.2 mL of 1.0 M HCl aqueous solution was added at 0 C. The mixture was allowed to warm to room temperature and stirred for 4 hours. The reaction was quenched by 1.0 M NaHCO3 aqueous solution and the aqueous layer was washed with diethyl ether (3 x 2.0 mL) and the combined organic layers were dried over Na2SO4 and concentrated under reduced pressure to afford oil, which is purified by silica gel chromatography (5:1 petroleum ether/EtOAc) to deliver the desired product.


Key Words

1,5-keto carboxylic esters


ID: J54-Y2023