Palladium-Catalyzed One-Pot Cross-Coupling of Phenols Using Nonafluorobutanesulfonyl Fluoride

Abstract

Palladium-catalyzed coupling reactions, such as the ­Suzuki–Miyaura, Sonogashira, Stille, and Buchwald–Hartwig ­couplings, of phenols using nonafluorobutanesulfonyl fluoride (NfF) are described. These reactions proceeded through the in situ nonaflation of phenols.

Key words

phenol - cross-coupling - palladium - boronic acid - ­nonaflate

• References and Notes


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• 12 Using Ph₃P instead of SPhos, a similar reaction of electron-donating phenol 1b with 3a provided only 23% NMR yield of biaryl 4b accompanied by the formation of nonaflate 2b (77% NMR yield). Accordingly, we have concluded that SPhos is the better ligand for the one-pot Suzuki–Miyaura coupling, and Ph₃P, which is much less expensive than SPhos, may be an alternative in some cases
• 13 For details, see Supporting Information

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• 15 General Procedure for the Suzuki–Miyaura Coupling of Phenols 1 (Table 2) An oven-dried 10 mL test tube was evacuated and backfilled with nitrogen. The test tube was charged with phenol 1 (0.50 mmol, 1.0 equiv), boronic acid 3 (0.75 mmol, 1.5 equiv or 1.5 mmol, 3.0 equiv), Cs₂CO₃ (1.5 mmol, 3.0 equiv), Pd₂(dba)₃ (0.0050 mmol, 1.0 mol%), and SPhos (0.010 mmol, 2.0 mol%). The test tube was sealed with a septum, evacuated, then backfilled with nitrogen (this sequence was repeated three times). To the test tube were added dry MeCN (0.50 M) and NfF (0.75 mmol, 1.5 equiv) via a syringe in this order using a nitrogen balloon, and then the reaction mixture was stirred at 60 °C for several hours. After cooling the reaction mixture to r.t., EtOAc (ca. 1.0 mL) was added. The mixture was filtered through a Celite cake, and the filtrate was concentrated under reduced pressure. The crude material was purified by column chromatography on silica gel to give the biaryl 4. General Procedure for the Sonogashira Coupling of Phenols 1 (Table 3) An oven-dried 10 mL test tube was evacuated and backfilled with nitrogen. The test tube was charged with phenol 1 (0.50 mmol, 1.0 equiv), Cs₂CO₃ (1.5 mmol, 3.0 equiv), [PdCl₂(MeCN)₂] (0.0050 mmol, 1.0 mol%), and XPhos (0.010 mmol, 2.0 mol%). The test tube was sealed with a septum, evacuated, then backfilled with nitrogen (this sequence was repeated three times). To the test tube were added dry MeCN (0.50 M), phenylacetylene (5, 1.5 mmol, 3.0 equiv), and NfF (0.75 mmol, 1.5 equiv) via a syringe in this order using a nitrogen balloon, and then the reaction mixture was stirred at 60 °C for 5 h. After cooling the reaction mixture to r.t., EtOAc (1 mL) was added. The mixture was filtered through a Celite cake, and the filtrate was concentrated under reduced pressure. The crude material was purified by column chromatography on silica gel to give the diarylacetylene 6. Procedure for the Stille Coupling of 4-Hydroxyacetophenone (1c, Scheme 2) An oven-dried 10 mL test tube was evacuated and backfilled with argon. The test tube was charged with LiCl (46 mg, 1.5 mmol) and evacuated overnight with heating at 150 °C. After cooling, the test tube was backfilled with argon. The test tube was charged with 4-hydroxyacetophenone (1c, 68 mg, 0.50 mmol), Cs₂CO₃ (240 mg, 0.75 mmol), and PdCl₂(PPh₃)₂ (7.0 mg, 0.0056 mmol). The test tube was sealed with a septum, evacuated, then backfilled with argon (this sequence was repeated three times). To the test tube were added dry DMF (1.0 mL, 0.50 M), tributylvinyltin (7, 61 mg, 0.65 mmol), and NfF (0.13 mL, 0.75 mmol) via a syringe in this order using an argon balloon, then the reaction mixture was stirred at 60 °C for 6 h. After cooling, H₂O was added to the reaction mixture. The reaction mixture was extracted with Et₂O, and the resulting aqueous layer was extracted twice with Et₂O. The combined organic layers were washed with a sat. aq NaCl solution and dried over anhyd Na₂SO₄. The solution was filtered through a glass filter, then the filtrate was concentrated under reduced pressure. The crude product was purified by flash column chromatography on silica gel (hexane–EtOAc = 50:1) to give 4-vinylacetophenone (8, 64 mg, 87%) as a colorless solid. Procedure for the Buchwald–Hartwig Reaction of p-Methoxyphenol (1b, Scheme 3) An oven-dried 10 mL test tube was evacuated and backfilled with argon. The test tube was charged with 4-methoxy-phenol (1b, 62 mg, 0.50 mmol), aniline (9, 61 mg, 0.65 mmol), Cs₂CO₃ (490 mg, 1.5 mmol), Pd₂(dba)₃ (6.9 mg, 0.0075 mmol), and XPhos (14 mg, 0.030 mmol). The test tube was sealed with a septum, evacuated, then backfilled with argon (this sequence was repeated three times). To the test tube were added dry toluene (1.0 mL, 0.50 M) and NfF (0.13 mL, 0.75 mmol) via a syringe in this order using an argon balloon, then the reaction mixture was stirred at 105 °C for 15 h. After cooling the reaction mixture to r.t., EtOAc (1 mL) was added. The mixture was filtered through a Celite cake, and the filtrate was concentrated under reduced pressure. The crude product was purified by column chromatography on silica gel (hexane–EtOAc = 10:1) to give 4-methoxydiphenylamine (10, 90 mg, 90%) as a colorless solid