4-Oxo-4,5,6,7-tetrahydrobenzofuran-2-carboxylic acid was prepared from 1,3-cyclohexanedione and ethyl bromopyruvate. Dehydrogenation of this acid or its methyl ester gave 4-hydroxybenzofuran-2-carboxylic acid derivatives.
Dehydrogenation of the 4‐oxo‐4,5,6,7‐tetrahydrobenzofurans (IIIa) and (IIIb) gives optimal yields of the title compounds (V) and (VI) under the conditions A) and B), respectively.
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