Total synthesis of epothilone D by sixfold ring cleavage of cyclopropanol intermediates

The ring-opening or ring fragmentation reactions of cyclopropanol intermediates are used in the total synthesis of epothilone D for the creation of trisubstituted double bonds, an ethyl ketone functionality, as well as for the protection of carboxylic and ester groups. Epothilone D is obtained in 1.6% overall yield (24 steps in the longest linear sequence) starting from (R)-methyl 2,3-O-isopropylideneglycerate. The key cyclopropanol intermediates are efficiently obtained by titanium(IV)-catalyzed reactions of readily available esters with Grignard reagents.