New syntheses of pulvinic acids via reformatsky-type reactions with aryl-methoxymaleic anhydrides

Abstract

The reaction of zinc enolates, viz(13), derived from arylacetates with 2-aryl-3-methoxymaleic anhydrides gives β-hydroxy ester intermediates viz(17) which can be dehydrated to Z- and E- isomers of permethylated pulvinic acids. Thus, the intermediate (17) derived from (15) and (16) produces the Z- and E-isomers (23) and (24) respectively, of permethylated gomphidic acid. In a similar manner, the geometrical isomers of permethylated isogomphidic acid [(27) and (28)] and methyl leprapinate [(29) and (30)] are synthesised from appropriate arylacetate and aryl methoxymaleic anhydride precursors.

Treatment of permethylated pulvinic acids with trimethylsilyl iodide provides a facile method of producing the corresponding pulvinic acids. By this method gomphidic acid (2), isogomphidic acid (31) and atromentic acid (32b) have been prepared. Both (2) and (32b) were identical with the natural metabolites isolated from Gomphidius glutinosus and Xerocomus chrysenteron respectively.