Iodine-Mediated Oxidative Dehydrogenation of β-Acylamino Ketones for the Highly Stereoselective Synthesis of (Z)-β-Keto­enamides

Abstract

An iodine-mediated oxidative dehydrogenation of β-acylamino ketones has been developed for the synthesis of β-ketoenamides in moderate to good yields. Only Z-isomers are accessed due to the intramolecular H-bonding interaction in the HI-elimination step.

Key words

molecular iodine - dehydrogenation - β-acylamino ketones - β-ketoenamide - Z-selectivity

• References and Notes

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• 17 General Procedure for Iodine-Mediated Oxidative Dehydrogenation A 10 mL oven-dried reaction vessel was charged with 1a (53 mg, 0.2 mmol), DABCO (67 mg, 0.6 mmol), and iodine (61 mg, 0.24 mmol) in p-xylene (2.0 mL). The resulting solution was stirred at 60 °C for 5 h. After the reaction was complete, sat. Na₂S₂O₃ aq solution (10 mL) was added to quench the reaction, and the mixture was extracted by EtOAc (3 × 10 mL). The organic layer was separated and dried over anhydrous Na₂SO₄. After the removal of the solvent in vacuo, the residue was purified by flash column chromatography with PE–EtOAc (9:1) to give 2a. (Z)-N-(3-Oxo-1,3-diphenylprop-1-en-1-yl)acetamide (2a) Yield 27 mg (60%); reaction time 5 h; white solid; mp 60–62 °C; R_f = 0.35 (PE–EtOAc = 4:1). ¹H NMR (400 MHz, CDCl₃): δ = 12.27 (s, 1 H), 7.98–7.95 (m, 2 H), 7.57 (tt, 1 H, J = 4.8, 0.8 Hz), 7.50–7.46 (m, 4 H), 7.45–7.40 (m, 3 H), 6.33 (s, 1 H), 2.25 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 191.7, 168.9, 156.3, 138.6, 136.2, 132.7, 129.8, 128.7, 128.1, 127.8, 127.4, 104.8, 25.1. ESI-HRMS: m/z calcd for C₁₇H₁₆NO₂ [M + H]⁺: 266.1176; found: 266.1179.
• 18 (Z)-Ethyl (3-Oxo-1,3-diphenylprop-1-en-1-yl)carbamate (2s) Yield 44 mg (75%); reaction time 2 h; yellow oil; R_f = 0.51 (PE–EtOAc = 9:1). ¹H NMR (400 MHz, CDCl₃): δ = 11.95 (s, 1 H), 7.97 (d, 2 H, J = 7.2 Hz), 7.57–7.41 (m, 8 H), 6.28 (s, 1 H), 4.13 (q, 2 H, J = 7.2 Hz), 1.26 (t, 3 H, J = 7.2 Hz). ¹³C NMR (100 MHz, CDCl₃): δ = 191.2, 157.0, 152.9, 138.7, 136.0, 132.5, 129.8, 128.6, 128.0, 127.8, 127.5, 103.5, 61.9, 14.2. ESI-HRMS: m/z calcd for ­C₁₈H₁₇NO₃Na [M + Na]⁺: 318.1101; found: 318.1104.
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