Thionyl Chloride → 4-Oxo-4H-chromene-3-carbonitrile

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The present invention concerns a novel method of preparing these 3-cyanochromones from chromone-3-carboxylic acids. The reaction mechanism of the present invention may best be described by the following reaction scheme: ##STR4## Referring to the reaction scheme, chromone-3-carboxylic acid is initially converted to the acyl chloride by treating with thionyl chloride as disclosed in U.S. Pat. No. 3,849,446 to Von Strandtmann, et al., issued Nov. 19, 1974. The acyl chloride is then converted to the corresponding chromone-3-carboxamide, as disclosed in U.S. Pat. No. 3,862,143. The critical feature of the present invention is the further dehydration of the chromone-3-carboxamide with thionyl chloride in N,N-dimethylformamide to give the desired 3-cyanochromone in a high yield of at least 75%. Generally, a molar excess of thionyl chloride and a 30-40 molar excess of N,N-dimethylformamide are employed.

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