Novel One-Pot Synthesis of 3-Phenylnaphtho[2,3-b]furan and 3-Phenylbenzofurans Under Microwave Irradiation and Solvent-Free Conditions

Abstract

A one-pot synthesis of functionalized benzofurans has been developed via O-alkylation, carbon–carbon coupling/cyclization, and dehydration/olefination tandem reactions from phenacyl bromide and phenols under microwave irradiation and solvent-free conditions in the presence of mineral-supported reagent and inorganic base. The best selectivity for forming benzofuran product has been achieved with Na₂CO₃ as a base. The order of activity of inorganic base is as follows: K₂CO₃ > NaHCO₃ > Na₂CO₃ > KHCO₃ > Na₂SO₃ > KOH > K₃PO₄ > NaOH > KH₂PO₄ > KOAc. This novel synthesis features three new bonds and one ring system assembled in a single step.

Keywords:

• Benzofurans
• microwave assisted
• one pot
• solid phase
• tandem reaction

ACKNOWLEDGMENT

We are grateful for the financial support of the National Natural Science Foundation of China (NSFC 20773055 and 20021001).

Notes

^a Isolated yield.

Note. Reaction conditions: phenacyl bromide, 995 mg (5 mmol); naphthalene (5 mmol); inorganic base (2.5 mmol); and Al₂O₃ (5.2 g).

^a Isolated yield.

Note. Reaction conditions: phenacyl bromide (5 mmol); naphthalene (5 mmol); K₂CO₃; 350 mg (2.5 mmol); MSR (5.2 g).

^a Isolated yield.

Note. Reaction conditions: phenacyl bromide (5 mmol); naphthalene (5 mmol); Al₂O₃ (5.2 g).

^a Isolated yield.

^b CEM Discover instrument using an open vessel.

Note. Reaction conditions: phenacyl bromide, 995 mg (5 mmol); naphthalene (5 mmol); Al₂O₃ (5.2 g); K₂CO₃, 350 mg (2.5 mmol).

^a Isolated yield.

Note. Reaction conditions: phenacyl bromide, 995 mg (5 mmol); phenols (5 mmol); Al₂O₃ (3 equivalents of substrate, w/w).