Benzo(B)Thiophene → 1-Benzothiophene-2-carbaldehyde

Participants

Reaction Conditions

Reaction Steps

To a solution of thianaphthene (1.45 g, 10.5 mmol (97% pure)) in anhydrous Et2O (20 mL) at -15° C. was added dropwise a 1.6M solution of n-BuLi in hexane (9.9 mL, 15.7 mmol). The mixture was stirred at -15° C. (1.75 h) and at 25° C. (15 min). After recooling to -15° C., anhydrous N-methylformanilide (1.6 mL, 12.7 mmol) (distilled from CaH2) was added dropwise and the mixture was heated at reflux (30 min). The reaction mixture was quenched by addition of a mixture of 3N HCl (9 mL) and ice chips (20 mL). The organic phase was separated and the aqueous phase was extracted with Et2O (3×75 mL). The combined organic layers were washed with 1N HCl (3×40 mL), saturated aq. NaHCO3 (40 mL), dried (MgSO4), and evaporated to dryness. The residue was dissolved in EtOH (3 mL) and mixed with saturated aq. NaHSO3 (15 mL). The resulting mixture was allowed to stand for 30 min and the crystalline bisulfite addition product was collected by filtration, washing with Et2O (50 mL) and dried in a vacuum desicator. The yellow solid was dissolved in warm H2O (30 mL) and cooled to 0° C. Saturated aq. Na2CO3 was added and the mixture was stirred at 25° C. for 15 min. Filtration, washing with H2O and drying afforded benzo[b]thiophene-2-carboxaldehyde as an amorphous solid (1.25 g, 7.68 mmol) in 73% yield.

Provenance & Evidence