A Facile Synthesis of 1,1-Difluoroallenes from Commercially Available 1,1,1-Trifluoro-2-iodoethane

Abstract

1,1-Difluoroallenes are synthesized in good yield via zinc-promoted 1,2-elimination of 3,3-difluoro-2-iodoallylic acetates, which are prepared by the reaction of aldehydes or ketones with 1-iodo-2,2-difluorovinyllithium, generated from commercially available 1,1,1-trifluoro-2-iodoethane.

fluorinated allenes - metalation - carbanions - elimination - difluorovinylidenation

References

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10

The lithiation of CF₃CH₂I with BuLi instead of LDA at
-93 to -85 ˚C led to a low yield of 2,2-difluoro-1-iodovinyl-lithium, probably due to I-Li exchange reaction.

11

For 2-bromo-3,3-difluoroallylic acetates, zinc-promoted 1,2-elimination also took place readily at r.t. and led to the formation of the corresponding 1,1-difluoroallenes.

12

Mg was employed in THF to promote the 1,2-elimination of acetate 3d in vain.

13

When THF was used as a solvent, only a trace amount of 1g was observed by the ^¹9F NMR measurement in spite of a large excess amount of Zn and an extended reaction time. A similar behavior was exhibited by some other acetates 3 without a heteroaromatic ring.