Synthesis of C-Ring-Functionalized A-Ring-Aromatic Trichothecane Analogues

15,16-Dinor-4α-acetoxy-8-methoxy-6,8,10-trichothecatriene 12,13-epoxide (11) was prepared from 2α-(2-acetoxy-5-methoxyphenyl)-2β-methyl-3α-acetoxycyclopentanone (8) in three steps (bromination, DBN-induced cyclization, and spiroepoxidation). The cyclopentanone 8 was prepared from the hemiketal 6a which was prepared from 2'-acetoxy-5'-methoxyacetophenone (3f) in a reaction sequence involving the boron trifluoride catalyzed aldol addition of 1,2-bis(trimethylsilyloxy)cyclobutene followed by a trifluoroacetic acid catalyzed pinacol rearrangement of the cyclobutanone intermediate.