Samarium Metal Promoted Facile C-Acetylation of Baylis-Hillman Adducts in the Presence of Iron(III) Chloride and Iodine

Abstract

A novel and efficient strategy for the C-acetylation of Baylis-Hillman adducts has been described. Promoted by Sm(0)/Ac₂O/FeCl₃/I₂, the present method allows for the efficient con­version of Morita-Baylis-Hillman adducts to their corresponding 2-alkylidene-4-oxoalkanoate derivatives and reduction products.

Key words

Baylis-Hillman adduct - metallic samarium - C-acetylation - stereoselective

References and Notes

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All new compounds were characterized by ¹H NMR, ¹³C NMR, IR spectroscopy, and elemental analysis.

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The stereochemistry of product 2 was all E, as was that of product 3. [9c] The ¹H NMR spectrum of 2 was in good agreement with the reported data. [5]

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General Procedure for C-Acetylation of Baylis-Hillman Adducts
To a stirred solution of 6 mmol Sm powder (0.9 g) and
6 mmol Ac₂O (0.6 g) in 15 mL THF, 5 mol% FeCl₃, 4 mol% I₂ and 1 mmol Baylis-Hillman adduct 1 were added. The resulting mixture was then allowed to reflux in the air. Until completion of the reaction, 3 mL HCl (1 M) was then added to quench the reaction and the mixture was successively exacted with CH₂Cl₂ (3 × 20 mL). The organic phase was washed with 15 mL sat. brine, dried over anhyd Na₂SO₄, and filtered. The solvent was removed under reduced pressure to give the crude products, which were purified by column chromatography using EtOAc and PE (1:10) as eluent. Selected spectroscopic data for compounds 2 follow.
Compound 2a (R = Ph): ¹H NMR (500 MHz, CDCl₃): δ = 7.93 (s, 1 H), 7.37-7.27 (m, 5 H), 3.80 (s, 3 H), 3.62 (s, 2 H), 2.25 (s, 3 H). ¹³C NMR (500 MHz, CDCl₃): δ = 206.1, 167.8, 142.2, 135.0, 128.9, 128.7, 128.6, 126.6, 52.2, 42.5, 30.1. IR (film): 3058, 2952, 2847, 1703, 1639, 1575, 1492, 1437, 1359, 1264, 1098, 764, 700 cm^-1.
Compound 2b (R = 3-MeOC₆H₄): ¹H NMR (500 MHz, CDCl₃): δ = 7.90 (s, 1 H), 7.30-6.84 (m, 4 H), 3.81 (s, 3 H), 3.80 (s, 3 H), 3.63 (s, 2 H), 2.26 (s, 3 H). ¹³C NMR (500 MHz, CDCl₃): δ = 206.6, 168.4, 160.1, 142.8, 136.9, 130.2, 127.4, 121.6, 115.2, 114.5, 55.8, 52.8, 43.2, 30.7. IR (film): 3001, 2953, 2850, 1706, 1637, 1600, 1580, 1488, 1433, 1359, 1247, 1098, 790, 690 cm^-1.