A New, Highly Stereoselective Synthesis of β-Unsubstituted (Z)-γ-Alkylidenebutenolides Using Bromine as a Removable Stereocontrol Element.

Several β-unsubstituted (Z)-y-alkylidenebutenolides have been prepared in highly stereocontrolled fashion by implementing a steric directing group stratagem in the vinylogous aldol condensation of butenolides with aldehydes. Applications to the synthesis of the antitumor heptene (S)-melodorinol and a thiophenelactone from Chamaemelum nobile L. are described.