Approach to the Core Structure of Schweinfurthin B

摘要

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.