Silver ion-assisted solvolysis of trans-2,2-dibromo-1,3-dimethylcyclopropanecarboxylic acid: Selective formation of 4-bromo-3,5-dimethyl-2(5H)-furanone

The title compound has been solvolysed in 2,2,2-trifluoroethanol (IFE), iso propyl alcohol (IPA), 1,1,1,3,3,3-hexafluoro-2-propanol (HFP) and tert-buty l alcohol (TBA) in the presence of silver trifluoroacetate. The product dis tribution is sensitive to the solvent used. In TFE and IPA two major produc ts were formed, the butenolide 4-bromo-3,5-dimethyl-2 (SH)-furanone and the corresponding (Z)-4-alkoxy-3-bromo-2-methyl-2-pentenoic acid, but, in addi tion, minor amounts of 2-alkoxy-3-bromo-2-methyl-3-pentenoic acid and 3-bro mo-2-hydroxy-2-methyl-3-pentenoic acid were also obtained. In HFP and TEA t he furanone was formed in better than 80% yield, the other products being 3 -bromo-2-hydroxy-2-methyl-3-pentenoic acid and 3-bromo-2-methyl-2,4-pentadi enoic acid. The outcome of the reactions is discussed on the basis of the n ucleophilicity, the hydrogen-bonding ability and the polarity of the solven ts.