A total synthesis of herboxidiene methyl ester

The total synthesis of the methyl ester, 35, of herboxidiene (1, a.k.a. GEX1A and TAN-1609), a polyketide displaying both herbicidal and anti-tumor activity, is described. The convergent reaction sequence involves, in its closing stages, the union of the phosphine oxide 3 with the aldehyde 21 to deliver, via a Horner-Wittig reaction with accompanying epimerization at C12, compound 33 that after deprotection affords an alcohol, 34, capable of participating in a regioand diastereo-selective epoxidation reaction to give target 35. Phosphine oxide 3 was prepared via the intramolecular hetero-Michael addition of a secondary alcohol to a tethered and Z-configured acrylate while aldehyde 21 was generated, in the crucial step of the relevant reaction sequence, via an Ireland-Claisen rearrangement reaction.