A novel five-carbon homologation leading to 3,4-alkadienoic acids by SN2′ reaction of β-ethynyl-β-propiolactone with grignard reagents in the presence of copper(i) catalyst
β-Ethynyl,-β-propiolactone reacts regioselectively with Grignardreagents in the presence of copper(I) catalyst to afford 3,4-alkadienoic acids in high yields. Synthetic utility of this reaction is demonstrated in the simple synthesis of pellitorine.