subjected to Horner-Wadsworth-Emmons olefination9 with
TBS-protected glycolaldehyde to afford E-olefin 10 in 68%
overall yield. Careful treatment of 10 with TBAF/AcOH (1:3)
in THF at 0 °C gave allylic alcohol 5 in 79% yield. By contrast,
direct olefination reaction between phosphonate and a
glycolaldehyde dimer10 afforded allylic alcohol 5 in low yield
(23%, 53% based on recovered starting materials).