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

摘要

The Zn/Barbier reaction of acid-washed zinc or zinc/silver couple with (Z)- or (E)-CF_3CF=CFI and aromatic aldehydes in DMF stereospecifically gives the (Z)- or (E)-allylic alcohol, CF_3CF=CFCH(OH)C_6H_5. Substituted aromatic aldehydes, which contain an electronwithdrawing 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 #alpha#-H, fail to undergo Barbier addition and significant amounts of CF_3CF=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 CF_3CF-CFI to aromatic aldehydes is best explained by formation of the [CF_3CF=CF]~direct-anion which adds to the aldehyde and is not adequately explained by formation and addition of an unsolvated zinc reagent, CF_3CF-CFZnI (unsolvated).