Zinc(II) Iodide-Triethylsilane: A Novel Mild Reduction System for Direct Deoxygenation of Aryl Aldehydes, Ketones, and α,β-Unsaturated Enones

Abstract

ZnI₂-TESH has been found to be a novel mild and efficient reduction system. This reagent, in contrast to the traditional ionic deoxygenation systems (TFA-R₃SiH, BF₃˙OEt₂-R₃SiH, etc.), could directly deoxygenate different kinds of carbonyl compounds such as aryl aldehydes, ketones, and α,β-unsaturated enones to the corresponding hydrocarbons in moderate to excellent yields.

Key words

zinc iodide - ionic hydrogenation - deoxygenation - carbonyl compounds - hydrocarbons

References and Notes

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14

Deng, G.; Zhao, X. L.; Li, Z.; Jiang, B.; Li, Y. C. unpublished results.

19

General Procedure for the Synthesis of Product 2: To a stirred solution of substrate 1 (1 mmol) in 1,2-dichloroethane (5 mL) at r.t. was added solid zinc iodide (638 mg, 2 mmol).Then, triethylsilane (1.9 mL, 10 mmol) was added slowly to the above suspension via a syringe. The reaction mixture was stirred at r.t. until 1 was completely disappeared or there was no further conversion (TLC inspection). The stirring was stopped, and then the reaction mixture was filtered through Celite. The Celite was washed with CH₂Cl₂ (4 × 15 mL). The combined filtrate was washed with H₂O and sat. brine, and then dried over anhyd Na₂SO₄. After concentration, the residue was chromatographed on silica gel, eluting with 0-25% EtOAc in cyclohexane.

20

Analytic Data for 4-Chloro-2-[2,2,2-trifluoro-1-(triethyl-silyloxy)ethyl]aniline (2j): ^¹H NMR (300 MHz, CDCl₃): δ = 0.62 (q, J = 7.9 Hz, 6 H), 0.92 (t, J = 7.9 Hz, 9 H), 3.93 (br s, 2 H), 4.94 (q, J = 7.2 Hz, 1 H), 6.60 (d, J = 8.5 Hz,
1 H), 7.09 (dd, J = 8.5, 2.5 Hz, 1 H), 7.15 (d, J = 2.5 Hz, 1 H). MS (EI): m/z (%) = 339 (39) [M⁺], 322 (4), 310 (43), 190 (32), 188 (100), 77 (36). HRMS (EI): m/z calcd for C₁₄H₂₁NOSiClF₃: 339.1033; found: 339.1041.

23

Analytic Data for 5-[(4-Hydroxy-3-methoxyphenyl)-methyl]-2-methoxy-4-methylphenol (2d-2): ^¹H NMR (300 MHz, CDCl₃): δ = 2.19 (s, 3 H), 3.80 (s, 2 H), 3.82 (s, 3 H), 3.86 (s, 3 H), 5.39-5.56 (m, 2 H), 6.61 (d, J = 7.7 Hz, 1 H), 6.63 (s, 1 H), 6.68 (d, J = 3.2 Hz, 2 H), 6.82 (d, J = 7.7 Hz, 1 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 19.2, 38.4, 55.8, 56.0, 111.1, 112.9, 114.1, 116.0, 121.3, 127.7, 132.0, 132.4, 143.3, 143.7, 144.6, 146.4. IR (KBr): 3384, 3022, 2931, 2835, 1608, 1513, 1460, 1431 cm^-¹. MS (EI):
m/z (%) = 274 (100) [M⁺], 273 (6), 259 (33), 150 (38). HRMS (EI): m/z calcd for C₁₆H₁₈O₄: 274.1205; found: 274.1200.