New Synthesis of (±)-5-hydroxymarmesin,biogenetic precursor of the skin photosensitizing agent bergapten (5-MOP)

A convenient synthesis is described of (±)-5-hydroxymarmesin, 4-hydroxy-2-(1-hydroxy-1-methylethyl)-2,3-dihydro-7H-furo3,2-g]1]benzopyran-7-one, a physiological intermediate in the biogenetic pathway of 5-O-alkylfurocoumarins. The synthesis was achieved by a regiospecific 6-C isoprenylation of 5,7-diacetoxy-coumarin; the 6-C isoprenylated derivative is then submitted to an oxidative cyclization obtaining mainly the title compound together with its angular isomer.