Studies on Kojic Acid and its Relatedγ-Pyrone Compounds

An excellent synthetic method of maltol from kojic acid has been established. By Mannich reaction with formaldehyde and dimethylamine, comenic acid gave the mono-Mannich derivative which was reduced to 6-methyl comenic acid. The acid was converted to maltol in good yield by decarboxylation with copper powder or KC–400 (tetra-chloro-diphenyl). Hydroxymethylations of kojic, comenic and pyromeconic acids with formaldehyde in alkaline medium yielded the corresponding methylol derivatives which were converted to 6-methyl kojic acid, 6-methyl comenic acid and maltol in good yields, respectively, by reduction with stannous chloride. Oxidation of 6-methyl kojic acid with chromic anhydride and acetic acid gave 6-methyl comenic acid.