Extractives from Guttiferae. Part XXIII. An unambiguous synthesis of 6-deoxyjacareubin and related 3,3- and 1,1-dimethylallyl and annulated xanthones

Unambiguous syntheses are described of 6-deoxyjacareubin (1) and ether derivatives of the related metabolite 1,3,5-trihydroxy-2-(3-methylbut-2-enyl)xanthone (4). In addition, related pyrano-, furo- and (3,3-, and 1,1-dimethylallyl)-xanthones derived from 1,3,5- and 1,3,7-trihydroxyxanthone have been prepared. The nuclear Over-hauser effect can differentiate a linear pyranoxanthone from its angular isomer.