ACID-PROMOTED CYCLIZATION OF TETRONIC ACID TO ALKENE - CHEMICAL TRANSFORMATION OF (-)-IRCINIANIN TO (-WISTARIN())

The perchloric acid-promoted transformation of (-)-ircinianin (1) to ( +)-wistarin (2) is described. The reaction of I with perchloric acid i n acetonitrile gave 2 in 35% yield along with a positional isomer 4 in 35% yield. The structure of 4 was determined by two dimensional (2D) NMR studies, On the other hand, the reaction of 2-methyl-4-prenyltetro nic acid (6), as a model compound for the above transformation, gave t he cyclized product 8 corresponding to 2 in 58% yield and the keto-lac tone 9 in 22% yield under the same conditions.