A NEW SYNTHESIS OF XANTHONES - 2,4,7-TRICHLORONORLICHEXANTHONE AND 4,5,7-TRICHLORONORLICHEXANTHONE, 2 NEW LICHEN XANTHONES

A new synthetic route to norlichexanthone (1, 3, 6-trihydroxy-8-methyl-9H-xanthen-9-one) derivatives has been developed by using a Smiles rearrangement of an appropriately substituted depside in the key step. 2, 4, 7-Trichloronorlichexanthone (22) and 4, 5, 7- trichloronorlichexanthone (29) have been prepared by this method. The former xanthone (22) was shown to be a constituent of the lichens Lecanora sulphurata and L flavo-pallescens and the latter (29) a constituent of Micarea austroternaria var. isabellina. © 1990 ASEG.