On the synthesis of cepacin A

Efforts directed toward a total synthesis of cepacin A is presented in full detail. The C-7, C-8, and C-9 stereogenic centers in the target molecule were derived from d-arabinose. The configuration of the allene axis was controlled at the bromoallenation step by the C-10 configuration of the precursor. An unexpected yet very interesting phenomenon was observed with the bromoallenation, where the α-isomer of the propargylic alcohol 31 was entirely resistant to the conditions that worked so well for its β-counterpart. The problem was eventually solved by careful tuning of the size of the neighboring groups based on the clue obtained from conformational analysis. The diyne moiety was incorporated into the molecular framework through a coupling of the TMS protected diyne with a proper bromoallene under the Sonogashira conditions with EtOAc as the solvent. Use of other solvents at this step led to complete failure.