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

We have developed a gold(I)-catalyzed intramolecular cyclization of gamma- and delta- 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. (c) 2007 Elsevier Ltd. All rights reserved.