Chemoselective Transfer Hydrogenation of α,β-Unsaturated Ketones Catalyzed by Iridium Complexes

Abstract

Efficient chemoselective transfer hydrogenation of the C=C bond of α,β-unsaturated ketones has been developed, using the iridium complexes containing pyridine-imidazolidinyl ligands as catalysts and formic acid as a hydrogen source. In comparison with organic solvents or H₂O as solvent, the mixed solvents of H₂O and MeOH are critical for a high catalytic chemoselective transformation. This chemoselective transfer hydrogenation can be carried out in air, which is operationally simple, allowing a wide variety of α,β-unsaturated substrates with different functional groups (electron-donating and electron-withdrawing substituents) leading to chemoselective transfer hydrogenation in excellent yields. The practical application of this protocol is demonstrated by a gram-scale transformation.

Key words

transfer hydrogenation - iridium complex - α,β-unsaturated ketones - formic acid - chemoselective reduction

Publikationsverlauf

Eingereicht: 29. Dezember 2020

Angenommen nach Revision: 26. Januar 2020

Artikel online veröffentlicht:
08. Februar 2021

• References and Notes

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• 21 Procedure for the Preparation of 3To a 25.0 mL dried Schlenk tube was added the α,β-unsaturated ketone (2, 0.5 mmol), Ir catalyst (1.0 mol %), HCOOH (10.0 equiv), water (2.0 mL), and MeOH (2.0 mL) successively. The mixture was stirred at room temperature for 12 h under air. After reaction was complete, the mixture was diluted with H₂O (15.0 mL), neutralized with saturated aq. NaHCO₃, and extracted with EtOAc (3 × 10.0 mL). The combined organic layers were washed with brine (3 × 10.0 mL) and dried over anhydrous MgSO₄. After filtration and removal of the EtOAc under vacuum, the crude product was purified by column chromatography on silica gel, eluting with hexane or petroleum ether/ethyl acetate (10:1 to 50:1) to achieve the desired products.1,3-Diphenylpropan-1-one (3aa)^12b Yield 90% (94.5 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.00 (d, J = 7.8 Hz, 2 H), 7.59 (t, J = 7.3 Hz, 1 H), 7.49 (t, J = 7.7 Hz, 2 H), 7.37–7.22 (m, 5 H), 3.37–3.30 (m, 2 H), 3.14–3.07 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.3, 141.3, 136.9, 133.1, 128.6, 128.6, 128.5, 128.1, 126.2, 40.5, 30.2.1-Phenyl-3-(p-tolyl)propan-1-one (3ab)¹⁴ Yield 90% (96.3 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.98–7.92 (m, 2 H), 7.55 (t, J = 7.4 Hz, 1 H), 7.45 (t, J = 7.7 Hz, 2 H), 7.13 (q, J = 8.1 Hz, 4 H), 3.31–3.24 (m, 2 H), 3.06–3.00 (m, 2 H), 2.32 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.4, 138.2, 136.9, 135.7, 133.1, 129.2, 128.6, 128.3, 128.1, 40.6, 29.7, 21.0.1-Phenyl-3-(m-tolyl)propan-1-one (3ac)^2d Yield 86% (95.2 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.96 (d, J = 7.5 Hz, 2 H), 7.55 (t, J = 7.3 Hz, 1 H), 7.45 (t, J = 7.6 Hz, 2 H), 7.19 (t, J = 7.5 Hz, 1 H), 7.04 (dd, J = 13.2, 9.1 Hz, 3 H), 3.33–3.26 (m, 2 H), 3.06–2.99 (m, 2 H), 2.33 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.4, 141.3, 138.1, 136.9, 133.1, 129.3, 128.6, 128.5, 128.1, 126.9, 125.4, 40.6, 30.1, 21.4.3-(2-Methoxyphenyl)-1-phenylpropan-1-one (3ad)¹⁴ Yield 85% (102 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.97 (d, J = 7.8 Hz, 2 H), 7.53 (t, J = 7.3 Hz, 1 H), 7.43 (t, J = 7.6 Hz, 2 H), 7.23–7.16 (m, 2 H), 6.92–6.81 (m, 2 H), 3.81 (s, 3 H), 3.29–3.22 (m, 2 H), 3.08–3.01 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 200.0, 157.6, 137.0, 132.9, 130.2, 129.6, 128.6, 128.2, 127.6, 120.6, 110.3, 55.2, 39.0, 25.8.3-(4-Chlorophenyl)-1-phenylpropan-1-one (3ae)¹⁴ Yield 90% (109.8 mg), colorless oil (88.5–90 °C). ¹H NMR (400 MHz, CDCl₃): δ = 7.98–7.91 (m, 2 H), 7.56 (t, J = 7.4 Hz, 1 H), 7.45 (t, J = 7.7 Hz, 2 H), 7.28–7.24 (m, 2 H), 7.18 (d, J = 8.4 Hz, 2 H), 3.28 (t, J = 7.5 Hz, 2 H), 3.04 (t, J = 7.5 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.9, 139.7, 136.8, 133.2, 131.9, 129.8, 128.7, 128.6, 128.0, 40.2, 29.4.3-(4-Bromophenyl)-1-phenylpropan-1-one (3af)¹⁴ Yield 83% (119.5 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.04–7.95 (m, 2 H), 7.58 (dd, J = 10.7, 4.0 Hz, 2 H), 7.48 (t, J = 7.6 Hz, 2 H), 7.35 (dd, J = 7.6, 1.6 Hz, 1 H), 7.27 (td, J = 7.5, 1.1 Hz, 1 H), 7.10 (td, J = 7.7, 1.7 Hz, 1 H), 3.37–3.32 (m, 2 H), 3.24–3.19 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.9, 140.6, 136.8, 133.2, 132.9, 130.8, 128.6, 128.1, 128.0, 127.7, 124.4, 38.6, 30.8.3-(2,3-Difluorophenyl)-1-phenylpropan-1-one (3ag)Yield 81% (99.6 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.01–7.95 (m, 2 H), 7.59 (t, J = 7.4 Hz, 1 H), 7.48 (t, J = 7.7 Hz, 2 H), 7.08–6.98 (m, 3 H), 3.34 (t, J = 7.5 Hz, 2 H), 3.15 (t, J = 7.5 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.6, 149.9 (dd, J = 243, 13 Hz), 136.6, 133.2, 130.6 (d, J = 12 Hz), 128.7, 128.0, 125.6 (t, J = 4 Hz), 123.9 (dd, J = 6, 4 Hz), 115.2 (d, J = 17 Hz), 38.6, 23.6.3-(2,3-Dimethylphenyl)-1-phenylpropan-1-one (3ah)Yield 86% (102.3 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.00 (d, J = 7.6 Hz, 2 H), 7.59 (t, J = 7.4 Hz, 1 H), 7.49 (t, J = 7.6 Hz, 2 H), 7.11–7.05 (m, 3 H), 3.27 (dd, J = 9.3, 6.5 Hz, 2 H), 3.15–3.08 (m, 2 H), 2.33 (s, 3 H), 2.28 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.5, 139.3, 137.1, 136.9, 134.6, 133.1, 128.6, 128.1, 128.1, 126.9, 125.6, 39.6, 28.3, 20.7, 15.1. ESI-HRMS: m/z calcd for C₁₇H₁₉O [M + H]⁺: 239.1436; found: 239.1433.3-(Furan-2-yl)-1-phenylpropan-1-one (3ai)^22a Yield 82% (82 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.99–7.95 (m, 2 H), 7.56 (t, J = 7.4 Hz, 1 H), 7.45 (t, J = 7.7 Hz, 2 H), 7.33–7.28 (m, 1 H), 6.30–6.25 (m, 1 H), 6.05 (d, J = 3.1 Hz, 1 H), 3.35–3.31 (m, 2 H), 3.11–3.07 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.7, 154.8, 141.1, 136.8, 133.2, 128.6, 128.1, 110.3, 105.3, 36.9, 22.5.1-Phenyl-3-(thiophen-2-yl)propan-1-one (3aj)^22b Yield 80% (86.4 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.98–7.93 (m, 2 H), 7.55 (t, J = 7.4 Hz, 1 H), 7.45 (t, J = 7.6 Hz, 2 H), 7.11 (dd, J = 5.1, 0.9 Hz, 1 H), 6.91 (dd, J = 5.0, 3.5 Hz, 1 H), 6.85 (d, J = 3.1 Hz, 1 H), 3.38–3.33 (m, 2 H), 3.31–3.26 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.6, 143.9, 136.8, 133.2, 128.7, 128.1, 126.9, 124.7, 123.4, 40.6, 24.2.1-(4-Fluorophenyl)-3-phenylpropan-1-one (3ba)^2d Yield 88% (100.3 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.99–7.93 (m, 2 H), 7.32–7.18 (m, 5 H), 7.09 (t, J = 8.6 Hz, 2 H), 3.25 (t, J = 7.7 Hz, 2 H), 3.05 (t, J = 7.6 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 197.6, 165.7 (d, J = 253 Hz), 141.2, 133.3 (d, J = 2 Hz), 130.7 (d, J = 9 Hz), 128.60, 128.5 (d, J = 14 Hz), 126.2, 115.7 (d, J = 22 Hz), 40.4, 30.1. ESI-HRMS: m/z calcd for C₁₅H₁₄OF [M + H]⁺: 229.1029; found: 229.1030.1-(4-Chlorophenyl)-3-phenylpropan-1-one (3bb)^2d Yield 84% (102.5 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.91–7.86 (m, 2 H), 7.42 (d, J = 8.5 Hz, 2 H), 7.31–7.20 (m, 5 H), 3.26 (dd, J = 10.0, 5.3 Hz, 2 H), 3.06 (dd, J = 10.0, 5.2 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.0, 141.1, 139.5, 135.2, 129.5, 128.9, 128.,6 128.4, 126.2, 40.4, 30.1.1-(4-Bromophenyl)-3-phenylpropan-1-one (3bc)^2d Yield 83% (119.5 mg), yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.84 (d, J = 8.5 Hz, 2 H), 7.61 (d, J = 8.5 Hz, 2 H), 7.36–7.22 (m, 5 H), 3.29 (t, J = 7.7 Hz, 2 H), 3.09 (t, J = 7.6 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.2, 141.1, 135.6, 131.9, 129.6, 128.6, 128.4, 128.3, 126.3, 40.4, 30.1.3-Phenyl-1-[4-(trifluoromethyl)phenyl]propan-1-one (3bd)^2d Yield 80% (111.2 mg), yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.07 (d, J = 8.2 Hz, 2 H), 7.74 (d, J = 8.3 Hz, 2 H), 7.36–7.22 (m, 5 H), 3.35 (t, J = 7.6 Hz, 2 H), 3.11 (t, J = 7.6 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.2, 140.9, 139.5, 134.6 (q, J = 33 Hz), 128.6, 128.4, 128.4, 126.3, 125.7 (q, J = 4 Hz), 123.5 (q, J = 258 Hz), 40.8, 29.9.1-(3-Bromo-4-fluorophenyl)-3-phenylpropan-1-one (3be)Yield 87% (133.1 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.19 (dd, J = 6.6, 2.1 Hz, 1 H), 7.92 (ddd, J = 8.5, 4.7, 2.1 Hz, 1 H), 7.36–7.30 (m, 2 H), 7.28–7.18 (m, 4 H), 3.28 (t, J = 7.6 Hz, 2 H), 3.09 (t, J = 7.6 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 196.5, 162.0 (d, J = 244 Hz), 140.9, 134.4 (d, J = 3 Hz), 134.0 (d, J = 1 Hz), 129.2 (d, J = 8 Hz), 128.6, 128.4, 126.3, 116.7 (d, J = 23 Hz), 109.9 (d, J = 22 Hz), 40.4, 30.0. ESI-HRMS m/z calcd for C₁₅H₁₃OBrF [M + H]⁺: 307.0134; found: 307.0135.1-(4-Nitrophenyl)-3-phenylpropan-1-one (3bf)^22c Yield 81% (103.3 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.32 (d, J = 8.8 Hz, 2 H), 8.11 (d, J = 8.8 Hz, 2 H), 7.36–7.30 (m, 2 H), 7.27 (dd, J = 11.1, 4.1 Hz, 3 H), 3.37 (t, J = 7.6 Hz, 2 H), 3.12 (t, J = 7.5 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 197.7, 150.3, 141.3, 140.6, 129.1, 128.7, 128.4, 126.4, 123.9, 41.0, 29.9.3-Phenyl-1-(p-tolyl)propan-1-one (3bg)^2d Yield 90% (100.8 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.90 (d, J = 8.2 Hz, 2 H), 7.36–7.23 (m, 7 H), 3.34–3.28 (m, 2 H), 3.13–3.07 (m, 2 H), 2.44 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 198.9, 143.9, 141.4, 134.4, 129.3, 128.6, 128.5, 128.2, 126.1, 40.4, 30.3, 21.7.1-(4-Methoxyphenyl)-3-phenylpropan-1-one (3bh)¹⁴ Yield 92% (110.4 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.72 (dd, J = 7.7, 1.7 Hz, 1 H), 7.51–7.46 (m, 1 H), 7.28 (dq, J = 21.7, 7.4 Hz, 5 H), 7.06–6.97 (m, 2 H), 3.91 (s, 3 H), 3.37–3.31 (m, 2 H), 3.09–3.03 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 201.8, 158.6, 141.8, 133.5, 130.4, 128.5, 128.4, 128.3, 125.9, 120.7, 111.5, 55.5, 45.5, 30.5.3-Phenyl-1-(thiophen-2-yl)propan-1-one (3bi)^12b Yield 87% (94.0 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.72 (d, J = 3.8 Hz, 1 H), 7.65 (d, J = 4.9 Hz, 1 H), 7.36–7.27 (m, 4 H), 7.24 (t, J = 7.5 Hz, 1 H), 7.14 (t, J = 4.3 Hz, 1 H), 3.29–3.24 (m, 2 H), 3.13–3.08 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 192.2, 144.2, 141.0, 133.6, 131.9, 128.6, 128.5, 128.1, 126.3, 41.2, 30.4.1-(Furan-2-yl)-3-phenylpropan-1-one (3bj)^12b Yield 81% (89.1 mg), pale yellow oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.59 (d, J = 0.9 Hz, 1 H), 7.34–7.19 (m, 6 H), 6.54 (dd, J = 3.5, 1.6 Hz, 1 H), 3.21–3.16 (m, 2 H), 3.07 (dd, J = 9.7, 5.3 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 188.5, 152.7, 146.4, 141.0, 128.5, 128.4, 126.2, 117.1, 112.2, 40.2, 30.0.1-(Naphthalen-1-yl)-3-phenylpropan-1-one (3bk)¹⁴ Yield 93% (120.9 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 8.60 (d, J = 8.5 Hz, 1 H), 8.01 (d, J = 8.2 Hz, 1 H), 7.91 (d, J = 7.9 Hz, 1 H), 7.85 (d, J = 7.2 Hz, 1 H), 7.64–7.55 (m, 2 H), 7.50 (t, J = 7.7 Hz, 1 H), 7.31 (dq, J = 12.0, 7.3 Hz, 5 H), 3.42 (t, J = 7.7 Hz, 2 H), 3.18 (t, J = 7.6 Hz, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 203.6, 141.2, 136.0, 134.0, 132.6, 130.2, 128.6, 128.5, 128.5, 127.9, 127.5, 126.5, 126.2, 125.8, 124.4, 43.9, 30.6.(E)-5-Phenyl-1-(2,6,6-trimethylcyclohex-2-en-1-yl)pent-1-en-3-one (3bl)Yield 78% (110.0 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.36–7.18 (m, 7 H), 6.15 (d, J = 16.3 Hz, 1 H), 2.96 (td, J = 14.1, 6.9 Hz, 4 H), 2.08 (t, J = 6.0 Hz, 2 H), 1.76 (s, 3 H), 1.65 (d, J = 2.8 Hz, 1 H), 1.49 (d, J = 5.6 Hz, 2 H), 1.07 (s, 6 H). ¹³C NMR (100 MHz, CDCl₃): δ = 199.7, 142.5, 141.4, 136.2, 136.0, 130.5, 128.5, 128.4, 126.1, 42.2, 39.7, 34.1, 33.6, 30.4, 28.8, 21.8, 18.9. ESI-HRMS m/z calcd for C₂₀H₂₇O [M + H]⁺: 283.2062; found: 283.2064.1,5-Diphenylpentan-3-one (3bm)^22d Yield 76% (90.4 mg), colorless oil. ¹H NMR (400 MHz, CDCl₃): δ = 7.31 (t, J = 7.4 Hz, 4 H), 7.22 (dd, J = 17.0, 7.3 Hz, 6 H), 2.93 (t, J = 7.6 Hz, 4 H), 2.75 (dd, J = 9.7, 5.5 Hz, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 209.2, 141.0, 128.5, 128.3, 126.1, 44.5, 29.8
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