Abstract
Copper(II) triflate effectively catalyzes the reaction of (trimethylsilyloxy)acrylic
esters and acetals to form γ-alkoxy-α-keto esters.
The reaction proceeds under mild conditions providing products in
good to excellent yields. The substrate scope was investigated,
and it was demonstrated that the products could be converted into
related compounds such as γ-hydroxy-α-keto esters
and α-oximes.
Key words
copper(II)triflate - acetals - (trimethylsilyloxy)acrylic ester - γ-alkoxy-α-keto ester - α-oximes - γ-hydroxy-α-keto ester - Mukaiyama-aldol
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General Procedure
for the Synthesis of the γ-Alkoxy-α-keto Esters
Cu(OTf)2 (0.04
mmol) was dissolved in dry CH2Cl2 (2 mL) and
cooled to 0 ˚C. The acetal (0.4 mmol) and the
acrylic ester (0.6 mmol) were added, and the reaction was monitored by
TLC. After consumption of the starting material, the crude reaction
mixture was directly subjected to column chromatography to yield
the pure products 3a-o.
Ethyl 4-Methoxy-4-phenyl-2-oxobutyrate (3a)
¹7
¹H
NMR (400 MHz, CDCl3): δ = 1.36
(t, J = 7.14
Hz, 3 H, CH3), 2.98 (dd, J = 16.8,
4.4 Hz, 1 H, CH2), 3.20 (s, 3 H, OCH3), 3.41
(dd, J = 16.8,
9.2 Hz, 1 H, CH2), 4.31 (q, J = 7.14
Hz, 2 H, CH2), 4.73 (dd, J = 9.2,
4.4 Hz, 1 H, CH), 7.29-7.40 (m, 5 H, Ar) ppm. ¹³C
NMR (100 MHz, CDCl3): δ = 13.9
(CH3), 47.5 (CH2), 56.7 (OCH3),
62.4 (CH2), 78.9 (CH), 126.4 (Ar), 128.0 (Ar), 128.5
(Ar), 140.1 (Ar), 160.6 (CO), 191.8 (CO) ppm.
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