Iodine → 1-(Benzo[b]thiophen-4-yl)-2-cyclopropylethan-1-one

Participants

Reaction Steps

A few drops of a solution of 4-bromobenzo[b]thiophene (2.84 g; prepared in a manner similar to that described in Example 9 Method A) in tetrahydrofuran (20 ml) was added under nitrogen to magnesium turnings (0.4 g). Two crystals of iodine were added and heat was applied to initiate the reaction. The remainder of the 4-bromobenzo[b]thiophene solution was added at reflux temperature over 20 minutes, then the mixture was heated under reflux for 2 hours. A solution of N-methoxy-N-methylcyclopropaneacetamide (2.0 g) in tetrahydrofuran (10 ml) was added, the mixture was heated under reflux for 2.5 hours, then it was stirred at ambient temperature for 18 hours and quenched by the addition of 2M hydrochloric acid (40 ml). The mixture was stirred at ambient temperature for 1 hour, then the product was extracted into ethyl acetate (3×30 ml). The combined extracts were washed with water (30 ml) and saturated aqueous sodium chloride solution (20 ml), dried (MgSO4), and the solvents were removed in vacuo. The residue was purified by flash chromatography over silica using petroleum ether (b.p. 60-80° C.) followed by a 95:5 mixture of petroleum ether (b.p. 60-80° C.) and ethyl acetate as eluants. Appropriate fractions were combined and the solvents removed in vacuo to give 1-(benzo[b]thiophen-4-yl)-2-cyclopropylethan-1-one (1.2 g) as a colourless oil which was used without further purification.

Provenance & Evidence