SYNTHESIS OF DISUBSTITUTED ACETYLENES, AND ITS APPLICATION TO THE STEREOSELECTIVE SYNTHESIS OF CONJUGATED TRIENES

Representative β-oxo-sulphones were obtained by (a) oxidation of β-hydroxy-sulphones, (b) oxidation of α-phenylthio-ketones, and (c) reaction of metallated sulphones with saturated and αβ-unsaturated esters. The β-oxosulphones were converted by way of lithium (in one example, sodium) enolates into enol phosphates, which on reductive elimination provided disubstituted acetylenes in moderate to good yield. The sequence permits the preparation of acetylenes R1C≡CR2 from the primary alcohols RCH2OH or equivalents. The value of the method is illustrated by a highly stereoselective synthesis from (E)-geraniol of the conjugated E,Z,E-triene (34) with retention of the original E-geometry.