The stereospecific Barbier reaction between (Z)- and (E)-1-iodopentafluoropropenes, zinc and aldehydes: Mechanistic aspects and scope of the preparation of (Z)- and (E)-partially fluorinated allylic alcohols

The Zn/Barbier reaction of acid-washed zinc or zinc/silver couple with (Z)- or (E)-CF3CFCFI and aromatic aldehydes in DMF stereospecifically gives the (Z)- or (E)-allylic alcohol, CF3CFCFCH(OH)C6H5. Substituted aromatic aldehydes, which contain an electron-withdrawing group, undergo Barbier addition reaction. Substituted aromatic aldehydes, which contain an electron-releasing group, fail to undergo Barbier addition reaction. Aliphatic aldehydes, such as butanal, which contain an α-H, fail to undergo Barbier addition and significant amounts of CF3CFCFH are formed. When the addition reaction is carried out in the presence of 1,4-dinitrobenzene, no reaction is observed. Mechanistically, the Zn/Barbier addition of CF3CFCFI to aromatic aldehydes is best explained by formation of the [CF3CFCF]⊖ anion which adds to the aldehyde and is not adequately explained by formation and addition of an unsolvated zinc reagent, CF3CFCFZnI (unsolvated).