A New Copper(I)-Catalyzed Cycloetherification/Acid-Catalyzed Allylic Nucleophilic Substitution for One-Pot Synthesis of 2-Substituted Benzofurans

Abstract

A new copper(I)-catalyzed cycloetherification followed by an acid-catalyzed allylic nucleophilic substitution have been developed for the one-pot synthesis of 2-substituted benzofurans. This one-pot reaction proceeds efficiently under extremely mild conditions with simple and inexpensive catalysts, providing diversely substituted benzofurans in good to excellent yields.

Key words

benzofurans - cycloetherifications - allylic nucleophilic substitution - copper - one-pot synthesis

• References and Notes

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• 10 See Table 3, entry 6 for detailed structure
• 11 General Procedure for Copper(I)-Catalyzed Cycloetherification: CuI (0.005 mmol, 1.0 mg), Ph₃P (0.005 mol, 1.3 mg) and Cs₂CO₃ (0.01 mmol, 3.3 mg) were added to a solution of phenol 1 (0.1 mmol) in MeOH (0.5 mL). The mixture was stirred at r.t. until the reaction was complete (monitored by TLC). After that the solvent was removed and the residue was purified by flash silica gel chromatography using n-hexane–EtOAc (4:1) as eluent to give the desired cycloetherification products
• 12 General Procedure for One-Pot Synthesis of 2-Substituted Benzofurans: CuI (0.005 mmol, 1.0 mg), Ph₃P (0.005 mol, 1.3 mg) and Cs₂CO₃ (0.01 mmol, 3.3 mg) were added to a solution of phenol 1 (0.1 mmol) in alcohol (0.5 mL). The mixture was stirred at r.t. for 4–6 h. After this time, p-TsOH (0.11 mmol, 20.9 mg) was added and the mixture was stirred at r.t. until the starting material was consumed. After that the mixture was diluted with Et₂O and washed with H₂O. The organic phase was separated, dried over Na₂SO₄, then concentrated and purified by silica gel chromatography using n-hexane–EtOAc (16:1) as eluent to give the desired benzofurans