A number of 1,2,3,4,4a,9a-hexahydro-9H-xanthen-9-ones have been prepared by the reaction of various phenols with 1-cyclohexene-1-carboxylic acids in the presence of polyphosphoric acid (PPA). However the reaction of 2,3-dimethylphenol gave in addition two isomeric 6,7-dimethyl-dodecahydro-indeno (1,2-a)xanthen-8,13-diones. 2,5-Dimethylphenol reacted differently giving the hexahydro-9H-fluoren-9-one instead. Dehydrogenation of the hexahydroxanthones with Pd/C in refluxing diphenyl ether afforded the corresponding xanthones in good yields (80–95%).
Volume 134, 2022
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