Hydrochloric Acid → Chromone

Participants

Reaction Steps

The keto-ester (Step 1) (19.2 g, 79.1 mmol), was added to trifluoroacetic anhydride (67.2 mL, 49.9 g, 475.8 mmol), potassium carbonate (44 g, 318 mmol) and toluene (400 mL). This suspension was stirred at room temperature for 36 hours, then heated to reflux for 4 hours. After cooling to room temperature, the suspension was poured over rapidly stirred (mechanical stirrer) ice (300 mL) and aqueous HCl (12 N, 50 mL). The resulting organic phase was separated from the clear mixture, was washed with water (5×500 mL), brine (1×500 mL), dried over MgSO4, filtered and concentrated in vacuo yielding tan solid which was dried under high vacuum. This sample was partially dissolved in heptane (100 mL) and ethyl acetate (12 mL) with heating on a steam bath, was filtered to remove insoluble material. The filtrate was allowed to cool to room temperature yielding the desired 4-oxo-4H-1-benzopyran as a fluffy tan solid (14.17 g, 56%): mp 106.7-108.6° C. This material was of suitable purity to use in the next step without further purification.

Provenance & Evidence