Chloroacetone → 1-[6-Methoxy-4-(phenylmethoxy)-2-benzofuranyl]ethanone

Participants

Reaction Steps

A solution of 2-(benzyloxy)-6-hydroxy-4-methoxybenzaldehyde (Example 1C, 3.46 g, 13.4 mmol) in N,N-dimethylformamide (50 mL) was treated with powdered anhydrous cesium carbonate (4.58 g, 14.05 mmol) added all at once. The resulting mixture was stirred in vacuo for 10 min. and then flushed with nitrogen. The reaction flask was placed in a water bath (22° C.) and treated with chloroacetone (1.74 g, 18.7 mmol) added dropwise over 5 min. The resulting mixture was then stirred at 22° C. for 18 h (no starting aldehyde left by tlc and formation of the intermediate alkylated aldehyde). The solid was filtered and washed with N,N-dimethylformamide. The filtrate was evaporated in vacuo and the residual oil was diluted with ethyl acetate (300 mL), washed with cold 0.1 N hydrochloric acid, saturated sodium bicarbonate and brine. After drying over anhydrous magnesium sulfate, evaporation of the solvent gave a thick syrup. This syrup was diluted with tetrahydrofuran (50 mL) and ethyl acetate (50 mL), treated p-toluenesulfonic acid monohydrate (0.2 g) and stirred at 20° C. for 1 h (tlc indicated complete cyclization of the intermediate alkylated aldehyde to the benzofuran). The reaction mixture was diluted with ethyl acetate (300 mL), washed with saturated sodium bicarbonate and brine. After drying over anhydrous magnesium sulfate, evaporation of the solvent gave a thick syrup. Chromatography on silica gel (4×12 cm, elution toluene-ethyl acetate 2-4%) gave 3.51 g (88% yield) of the title benzofuran as a yellow solid. Recrystallization from ethyl acetate (10 mL) and hexane (20 mL) gave the title material as large yellow prisms (3.15 g). LC (Method D): 2.148 min. HRMS (ESI) calcd for C18H17O4 [M+H]+ m/z 297.1121, found 297.1092. 1H NMR (CDCl3, 600 MHz) δ 2.51 (s, 3H), 3.82 (s, 3H), 5.13 (s, 2H), 6.37 (d, J=1.77 Hz, 1H), 6.63 (broad s, 1H), 7.34 (broad t, 1H), 7.39 (broad t, 2H), 7.44 (broad d, 2H), 7.55 (d, J=0.7 Hz, 1H).

Provenance & Evidence