Synthesis of rac- and ent-fridamycin E

Abstract Racemic fridamycin E ( »c -1) was synthesized in two ways: 1. Addition of lithium ∈rt -butyl acetate to ketone 15 followed by ether and ester cleavage to rac -1; 2. Grignard reaction of allylmagnesium bromide with 15 to rac -18 and subsequent ozonolysis, oxidation, methylation, ester and ether cleavage. The enantiomer θt -18 was obtained by Marschalk reaction of 7 with the chiral building block 20 derived from (S)-lactic acid. A similar reaction sequence converted θt -18 to ent -1 thus proving natural fridamycin E to be of (R)-configuration.