Cycloisomerization of γ- and δ-acetylenic acids catalyzed by gold(I) chloride

We have developed a gold(I)-catalyzed intramolecular cyclization of γ- and δ-alkyne acids in mild conditions yielding various alkylidene lactones. Whereas a slight electronic effect of the R group was observed on the regioselectivity, bulky substituents on the R group bearing the alkyne strongly modify the reactivity. The cycloisomerization of o-alkynylbenzoic methyl esters was achieved rather with AuCl3 as catalyst owing the presence of water affording exclusively the isocoumarins.