Synthesis of butenolides via a Horner-Wadsworth-Emmons cascading dimerization reaction

The efficient synthesis of a range of structurally related butenolides has been observed whilst we were exploring the substrate-scope of a Horner-Wadsworth-Emmons (HWE) reaction. Whilst aliphatic aldehydes gave the expected HWE product, aromatic aldehydes furnished butenolides, resulting from the dimerization of HWE product during desilylation of the initially formed HWE adduct. In addition to isolating butenolides in high yield, we have also determined precisely when dimerization occurs.