Tandem condensation of chiral α -alkoxy and α,β-dial-koxy aldehydes with allylic sulphinylanion, and thiophile promoted desulphurization of the resulting α-substituted allylic sulphoxide afford (E)-5-alkoxy-(or 5,6-dialkoxy)-2--alkene-1, 4-diols, advanced polyols precursors, the major stereochemical path occuring via a Felkin-Ahn (non chelation control) mode.