Lactones are not only very useful building blocks, but they also represent structural motifs in a variety of natural products with interesting biological activity. The transition metal-catalyzed intramolecular addition of a carboxylic acid to a terminal alkyne provides access to the ?-alkylidene lactone motif. Over the past years, numerous protocols based on transition-metals have been explored for this type of transformation. Unfortunately, most of these protocols require high catalyst loadings, prolonged reaction times, and/or elevated temperatures. In addition, the majority of the reports involve the use of homogeneous catalysis, which is generally associated with difficulties in recycling of the catalyst and additional purification steps to remove trace amounts of metal impurities from the final product. Herein, an efficient and highly regio- and stereoselective route for the cycloisomerization of acetylenic acids to ?-alkylidene lactones under relatively mild reaction conditions, using a heterogeneous Pd(II) catalyst is presented (Figure 1). The protocol tolerates the presence of different functional groups on both the a and ?-positions of the acetylenic acids. The heterogeneous Pd(II) catalyst showed high recyclability and a low leaching, making it an attractive option over previously developed homogeneous protocols. The present method is of potential use in the synthesis of biologically interesting lactones.

Cycloisomerization of acetylenic acids to <i>?</i>-alkylidene lactones using a palladium(II) catalyst supported on amino-funtionalized siliceous mesocellular foam

248th National Meeting (2014)

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Cycloisomerization of acetylenic acids to ?-alkylidene lactones using a palladium(II) catalyst supported on amino-funtionalized siliceous mesocellular foam