Carboxylate-Directed Tandem Functionalizations of α,β-Dihaloalkenoic Acids with 1-Alkynes: A Straightforward Access to (Z)-Configured, α,β-Substituted γ-Alkylidenebutenolides

An easy and mild copper(I)-catalysed lactonisation of readily available (E)-2,3-dihalopropenoic acid derivatives regio- and stereoselectively leads to rarely described (Z)-3-halo-5-ylidene-5H-furan-2-ones. These compounds are subsequently able to undergo classical Pd-catalysed cross-coupling reactions, providing 3-substituted and 3,4-disubstituted 5-ylidene-5H-furan-2-ones