Manganese(II)-Catalyzed Esterification of N-β-Hydroxyethyl­amides

Abstract

A catalyst system of manganese with 2,2-bipyridine for amide alcoholysis of N-β-hydroxyethylamides is described. This protocol enabled selective cleavage of the amide bond through a mechanism involving sequential N,O-acyl rearrangement and transesterification.

Key words

amides - esterification - manganese - selective reaction - acyl rearrangement

• References and Notes


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• 13 General Procedure for the Mn-Catalyzed Esterification (Table 2) An oven-dried Schlenk tube was equipped with Mn(acac)₂ (0.05 mmol), amide (1.0 mmol), 2,2′-bipyridine (0.05 mmol), diethyl carbonate (2.0 mmol), and n-BuOH (1.0 mL) and the resulting mixture was refluxed for periodic time under an argon atmosphere. After cooling to r.t., yields were determined by the following procedures: 1. Isolated yield; after removal of solvents in vacuo, the product was then isolated with column chromatography. 2. NMR yield; metal salts were removed by filtration through silica gel eluting with EtOAc, and solvents were removed in vacuo. Yield was determined by ¹H NMR analysis using phenanthrene as an internal standard. 3. GC yield; metal salts were removed by filtration through silica gel eluting with EtOAc, and yield was determined by GC analysis using dodecane as an internal standard. Butyl Cyclohexanecarboxylate (2b) Purified by flash column chromatography (silica gel, hexane–EtOAc = 20:1); colorless oil. ¹H NMR (400 MHz, CDCl₃, 30 °C): δ = 0.91 (t, J = 7.4 Hz, 3 H, CH₃), 1.12–1.66 (m, 10 H, methylene), 1.70–1.80 (m, 2 H, methylene), 1.80–1.90 (m, 2 H, methylene), 2.27 (tt, J = 3.7, 11.2 Hz, 1 H, COCH), 4.04 (t, J = 6.6 Hz, 2 H, OCH₂). ¹³C NMR (100 MHz, CDCl₃, 30 °C): δ = 13.6, 19.1, 25.4, 25.8, 29.0, 30.7, 43.3, 63.9, 176.1. Butyl 2-(Trifluoromethyl)benzoate (2j) Purified by flash column chromatography (silica gel, hexane–EtOAc = 20:1); colorless oil. IR (neat NaCl): ν = 2964 (m), 2876 (w), 1736 (s), 1316 (s), 1292 (s), 1264 (s), 1168 (s), 1144 (s) cm^–1. ¹H NMR (400 MHz, CDCl₃, 30 °C): δ = 0.96 (t, J = 7.5 Hz, 3 H, CH₃), 1.40–1.50 (m, 2 H, CH ₂CH₃), 1.70–1.80 (m, 2 H, OCH₂CH ₂), 4.34 (t, J = 6.7 Hz, 2 H, OCH₂), 7.50–7.60 (m, 2 H, Ar), 7.70–7.80 (m, 2 H, Ar). ¹³C NMR (100 MHz, CDCl₃, 30 °C): δ = 13.6, 19.0, 30.4, 65.9, 123.4 (q, J _C–F = 272 Hz), 126.6 (q, J _C–F = 5 Hz), 128.7 (q, J _C–F = 32 Hz), 130.1, 130.9, 131.6, 131.7, 167.0. ¹⁹F NMR (376 MHz, CDCl₃, 30 °C): δ = –58.1. MS–FAB⁺: m/z (relative intensity) = 247 (20) [M + H]⁺, 173 (40), 57 (100). HRMS–FAB⁺: m/z calcd for C₁₀H₁₁F₃NO₂: 247.0948 [M + H]⁺; found: 247.0946. For other compounds, see Supporting Information.

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• 16 Procedure of a Crossover Experiment (Scheme 2) An oven-dried Schlenk tube was equipped with Mn(acac)₂ (0.05 mmol), N-(2-hydroxyethyl)benzamide (1d) (1.0 mmol), N-hexyl-3-phenylpropionamide (4, 1.0 mmol), 2,2′-bipyridine (0.05 mmol), diethyl carbonate (2.0 mmol), and n-BuOH (1.0 mL), and the resulting mixture was refluxed for 18 h under an argon atmosphere. After cooling to r.t., metal salts were removed by filtration through silica gel eluting with EtOAc, and solvents were removed in vacuo. Yield and conversion were determined by ¹H NMR analysis using phenanthrene as an internal standard.