Synthesis of unit A of cryptophycin via a [2,3]-Wittig rearrangement

The synthesis of unit A of the cryptophycins from (S)-trans-3-penten-2-ol a nd from (S)-trans-4-hexen-3-ol has been completed. The key stereodeterminin g step is a [2,3]-Wittig rearrangement of a propargyl ether. Elaboration of the rearrangement product was accomplished by means of a selective hydrobo ration-oxidation of a terminal alkyne, Horner-Emmons homologation of the de rived aldehyde, followed by selective ozonolytic cleavage and Wittig olefin ation. This synthesis provides easy access to the series of cryptophycin an alogues that incorporate a modified aromatic ring in unit A.