Approach to the Core Structure of Schweinfurthin B

We investigated approaches to the xanthene part of schweinfurthin B. Starting from an exo‐methylene cyclohexanone, an organocuprate addition led to a cyclohexanone featuring a functionalized benzyl substituent in the 2‐position. Ring‐closing reactions to the tetrahydroxanthene core (formation of the central ring) were possible in moderate yield by attack of a phenolic oxygen function on the keto group. More effective was the cyclization to the xanthene core structure after conversion of the cyclohexanone to the exo‐methylene cyclohexane derivative and Lewis acid mediated addition of the phenolic OH to the double bond. In addition, we tried to form the xanthene ring system in a model study by cycloaddition reaction of a silyl enol ether with an ortho‐quinone methide.