Synthesis and Absolute Configuration of the 7-Phenylhepta-4,6-diyne-1,2-diol Isolated from Bidens pilosa

The title diynediol was synthesized in enantiopure (>98.4% ee) forms, with the cross coupling of phenylacetylene with either (R)- or (S)-5-benzyloxypent-1-yn-4-ol catalyzed by nickel(II) chloride-copper(I) iodide as the key step. Comparison of the spectroscopic data (especially the optical rotations) for the synthetic and natural samples revealed that the natural diynediol is of S-configuration. The unexpected formation of a pyranone ring at the alkyne terminal when cleaving a benzyl protecting group with acetic anhydride and trimethylsilyl triflate is also detailed; this approach illustrates a novel and mild entry to related pyranones.