Cycloisomerization of various γ-acetylenic acids to their corresponding γ-alkylidene lactones by the use of a heterogeneous Pd(II) catalyst supported on amino-functionalized siliceous mesocellular foam is described. Substrates containing terminal as well as internal alkynes were cyclized in high to excellent yields within 2-24 h under mild reaction conditions. The procotol exhibited high regio-and stereoselectivity, favoring the exo-dig product with high (Z)-selectivity. Moreover, the catalyst displayed excellent stability under the employed reaction conditions, as demonstrated by its good recyclability and low leaching.

Dep. Org. Chem., Arrhenius Lab., Univ. Stockholm, S-106 91 Stockholm, Swed.; Eng.) -U. Scheffler 30-122