5-Methoxy-2H-1-benzopyran-3-carboxylic acid → 5-Methoxy-3,4-dihydro-2H-chromene-3-carboxylic acid

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Reaction Steps

A mixture of 5-methoxy-2H-1-benzopyran-3-carboxylic acid (12.25 g, prepared in a similar manner to that described above), 10% palladium-on-carbon catalyst (3 g) and ethanol (250 ml) was hydrogenated at 1 atmosphere for 1 hour. Hydrogen uptake was slow, so further catalyst (3 g) was added, and hydrogenation continued for 5 hours. The mixture was filtered and the solvent removed in vacuo to leave a semisolid which crystallised from 2-propanol to give a mass of pale yellow crystals which was broken up, collected by filtration, washed with ice-cold 2-propanol, dried in vacuo, ground to a powder, and redried in vacuo to give 5-methoxy-3,4-dihydro-2H-1-benzopyran-3-carboxylic acid as a buff powder (7.4 g), m.p. 147°-150° C.

Provenance & Evidence