Toward a total synthesis of stigmatellin; obtention of an advanced fragment from gallic acid

Treatment by a base, then an acid, of the ester 3, which was prepared by starting from gallic acid 7a, afforded the chromone 6c, whose Swern oxidation, followed by condensation of the resulting aldehyde 6a with the trienyl lithium derivative 13b and methyl iodide, furnished products isomeric with, but not strictly identical to, an authentic sample of O-benzyl stigmatellin 1c.