Glyoxylic Acid → 3-Hydroxybenzofuran-2(3H)-one

Participants

Reaction Steps

4.9 g of 9-hydroxyphenanthrene, 4.1 g of 50% aqueous glyoxylic acid and 0.05 g of p-toluenesulfonic acid are heated for 2 h in 70 ml of 1,2-dichloroethane under a water separator. The precipitated solid is then cooled down, filtered off, washed with cold 1,2-dichloroethane and dried to leave 3.0 g of hydroxybenzofuranone, which is introduced in 20 ml of toluene as initial charge together with 1.5 ml of thionyl chloride and 3 drops of DMF and then gradually heated to 100° C. so that the evolution of HCl and SO2 remains lively, but still controllable. The reaction mixture is subsequently stirred at 100° C. for 1 h. About 20 ml of liquid are then distilled off to remove excess thionyl chloride. The residue is diluted with 10 ml of toluene and admixed at room temperature with 1.7 ml of triethylamine added dropwise. The thick blue reaction mixture is then refluxed for 2 h. The precipitated isoxindigo is filtered off after cooling down to room temperature, freed of the triethylamine hydrochloride by washing with water, dried and recrystallized from dichloromethane/ethanol to leave 1.3 g (47% of theory) of [3,3′]bi[1-oxacyclopenta[l]phenanthrenylidene]-2,2′dione of the formula:

Provenance & Evidence