Copper(I)-Catalyzed C-C and C-O Coupling Reactions Using Hydrazone ­Ligands

Abstract

Copper-catalyzed C-C coupling reaction of aryl iodides with diethylmalonate in toluene at 90 ˚C gave arylated malonates using 5 mol% of CuI with hydrazone 1a as a ligand in good yields under an aerobic atmosphere. We also found CuI/hydrazone 1b in toluene to be an efficient catalytic system for C-O coupling reactions of aryl bromides with phenols to give aryl ethers in good yields at 110 ˚C under an aerobic atmosphere.

Key words

copper catalyst - hydrazone - C-C coupling - C-O coupling - malonate - aryl ether

References and Notes

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8

We tried the reaction at 110 ˚C in toluene for 24 h, however, the yield of 2a decreased to 28% and ethyl phenylacetate was also obtained (8% NMR yield).

9

General procedure for copper-catalyzed C-arylation of diethyl malonate with aryl iodides (Table 2): Under an atmosphere of air, aryl iodide (2.0 mmol) was added to a mixture of diethyl malonate (4.0 mmol), Cs₂CO₃ (4.0 mmol), ligand 1a (0.20 mmol), and CuI (0.10 mmol) in toluene (2 mL) at r.t. The mixture was stirred at 90 ˚C for 24 h, then diluted with EtOAc and H₂O. The organic layer was washed with brine, dried over MgSO₄, and concentrated under reduced pressure. The resulting residue was purified by silica gel chromatography (hexane-EtOAc) to provide the desired product. All prepared compounds 2, except 2f, were previously known and identified by ^¹H NMR, ^¹³C NMR and MS.
Compound 2f (Table  [²] , entry 6): Yield: 53%; brown liquid; ^¹H NMR (CDCl₃): δ = 1.26 (t, J = 7.1 Hz, 6 H), 2.35 (s, 3 H), 4.16-4.27 (m, 4 H), 4.57 (s, 1 H), 7.13-7.28 (m, 4 H); ^¹³C NMR (CDCl₃): δ = 14.0, 21.4, 57.9, 61.7, 126.3, 128.4, 128.9, 129.9, 132.6, 138.2, 168.2; EI-MS: m/z (%) = 250 (25) [M⁺]; HRMS (FAB-MS): m/z calcd for C₁₄H₁₉O₄: 251.1283; found: 251.1284.

11

General procedure for copper-catalyzed O-arylation of phenols with aryl bromides (Table 4): Under an atmosphere of air, aryl bromide (0.5 mmol) was added to a mixture of phenol (1.0 mmol), K₃PO₄ (1.0 mmol), ligand 1b (0.025 mmol), and CuI (0.025 mmol) in toluene (1 mL) at r.t. The mixture was stirred at 110 ˚C for either 5 h or 18 h, then the mixture was diluted with EtOAc and H₂O. The organic layer was washed with brine, dried over MgSO₄, and concentrated under reduced pressure. The resulting residue was purified by silica gel chromatography (hexane-EtOAc) to provide the desired product. All prepared compounds 3, except 3g and 3h, were known and identified by ^¹H NMR, ^¹³C NMR and MS.
Compound 3g (Table  [4] , entry 7): Yield: 74%; colorless oil; ^¹H NMR (CDCl₃): δ = 2.34 (s, 3 H), 6.88 (d, J = 7.6 Hz, 2 H), 6.94-6.97 (m, 2 H), 7.15 (d, J = 8.6 Hz, 2 H), 7.35 (t, J = 8.0 Hz, 1 H), 7.45-7.54 (m, 2 H), 7.58 (d, J = 8.2 Hz, 1 H), 7.84-7.87 (m, 1 H), 8.22-8.25 (m, 1 H); ^¹³C NMR (CDCl₃): δ = 20.7, 112.6, 118.8, 122.1, 122.9, 125.8, 125.8, 126.5, 126.7, 127.7, 130.3, 132.8, 134.9, 153.6, 155.3; EI-MS: m/z (%) = 234 (100) [M⁺]; HRMS (FAB-MS): m/z calcd for C₁₇H₁₄O: 234.1045; found: 234.1027.
Compound 3h (Table  [4] , entry 8): Yield: 78%; colorless oil; ^¹H NMR (CDCl₃): δ = 2.31 (s, 3 H), 2.33 (s, 3 H), 6.77-6.80 (m, 2 H), 6.87-6.93 (m, 3 H), 7.12-7.21 (m, 3 H); ^¹³C NMR (CDCl₃): δ = 20.7, 21.4, 115.3, 119.0, 119.1, 123.6, 129.3, 130.2, 132.7, 140.0, 154.8, 157.7; EI-MS: m/z (%) = 198 (100) [M⁺]; HRMS (FAB-MS): m/z calcd for C₁₄H₁₄O: 198.1045; found: 198.1046.