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 th e (Z)- or (E)-allylic alcohol, CF3CF=CFCH(OH)C6H5. Substituted aromatic ald ehydes, which contain an electron-withdrawing group, undergo Barbier additi on reaction. Substituted aromatic aldehydes, which contain an electron-rele asing group, fail to undergo Barbier addition reaction. Aliphatic aldehydes , such as butanal, which contain an alpha -H, fail to undergo Barbier addit ion and significant amounts of CF3CF=CFH are formed. When the addition reac tion is carried out in the presence of 1,4-dinitrobenzene, no reaction is o bserved. Mechanistically, the Zn/Barbier addition of CF3CF=CFI to aromatic aldehydes is best explained by formation of the [CF3CF=CF](circle minus) an ion which adds to the aldehyde and is not adequately explained by formation and addition of an unsolvated zinc reagent, CF3CF=CFZnI (unsolvated). (C) 2001 Elsevier Science B.V. All rights reserved.