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

Participants

Reaction Steps

Approximately 3 ml of a solution of 4-bromobenzo[b]thiophene (1.85 g; prepared in a manner similar to that described in Bull. Soc. Chim. Fr., 1966, 111, 3667-3674) in tetrahydrofuran (20 ml) was added under nitrogen to a mixture of magnesium turnings (0.22 g) and tetrahydrofuran (2 ml). 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, the mixture was heated under reflux for 10 minutes, then it was cooled to ambient temperature. A solution of N-methoxy-N-methylpropionamide (1.01 g) in tetrahydrofuran (10 ml) was added, the mixture was heated under reflux for 30 minutes, then it was cooled to ambient temperature and quenched by the addition of 2M hydrochloric acid (25 ml). The mixture was allowed to stand at ambient temperature for 18 hours, then the tetrahydrofuran was removed in vacuo, the residue was diluted with water (50 ml) and the product was extracted into ethyl acetate (50 ml). The extract was washed with saturated aqueous sodium chloride solution (2×50 ml), dried (Na2SO4), and the solvents were removed in vacuo. The residue was purified by flash chromatography over silica using a 97:3 mixture of petroleum ether (b.p. 40-60° C.) and ethyl acetate as eluant. Appropriate fractions were combined and the solvents removed in vacuo to give 1-(benzo[b]thiophen-4-yl)propan-1-one (0.615 g) as a colourless oil which was used without further purification.

Provenance & Evidence