Carboxylate‐Directed Tandem Functionalisations 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 (see scheme).